1.
Lymph sinus
–
A lymph node or lymph gland, is an ovoid or kidney-shaped organ of the lymphatic system, and of the adaptive immune system, that is widely present throughout the body. They are linked by the vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a function, which is primarily dealt with by the liver. In the lymphatic system the lymph node is a secondary lymphoid organ, a lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla. Lymph nodes also have clinical significance and they become inflamed or enlarged in various diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the nodes is very important in cancer staging, which decides the treatment to be used. When swollen, inflamed or enlarged, lymph nodes can be hard, Lymph nodes are kidney or oval shaped and range in size from a few millimeters to about 1–2 cm long. Each lymph node is surrounded by a capsule, which extends inside the lymph node to form trabeculae. The substance of the node is divided into the outer cortex. The cortex is continuous around the medulla except where the medulla comes into contact with the hilum. Thin reticular fibers of reticular connective tissue, and elastin form a supporting meshwork called a reticulin inside the node, B cells, are mainly found in the outer where they are clustered together as follicular B cells in lymphoid follicles and the T cells are mainly in the paracortex. The number and composition of follicles can change especially when challenged by an antigen, elsewhere in the node, there are only occasional leucocytes. As part of the network there are follicular dendritic cells in the B cell follicle. The reticular network not only provides the support, but also the surface for adhesion of the dendritic cells. It allows exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses and these vessels are smaller and dont allow the passage of the macrophages so that they remain contained to function within the lymph node. In the course of the lymph, lymphocytes may be activated as part of the immune response
Lymph sinus
–
1) Capsule; 2) Subcapsular sinus; 3) Germinal centre; 4) Lymphoid nodule; 5) Trabeculae
Lymph sinus
–
Diagram of a lymph node, showing the flow of lymph through the
lymph sinuses.
Lymph sinus
–
Lymph node histology
Lymph sinus
–
There are clusters of nodes under the arms, in the groin, neck and abdomen
2.
Organ system
–
A biological system is a complex network of biologically relevant entities. On the micro to the scale, examples of biological systems are cells, organelles, macromolecular complexes. A biological system is not to be confused with a living system, for further information see e. g. definition of life or synthetic biology. These specific systems are studied in Human anatomy. Human systems are present in many other animals. Circulatory system, pumping and channeling blood to and from the body and lungs with heart, integumentary system, skin, hair, fat, and nails. Skeletal system, structural support and protection with bones, cartilage, ligaments, urinary system, kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine. Respiratory system, the used for breathing, the pharynx, larynx, bronchi, lungs. The lymphatic system includes functions including immune responses and development of antibodies, muscular system, allows for manipulation of the environment, provides locomotion, maintains posture, and produces heat. Includes skeletal muscles, smooth muscles and cardiac muscle, nervous system, collecting, transferring and processing information with brain, spinal cord and peripheral nervous system. The notion of system relies upon the concept of vital or organic function and this idea was already present in Antiquity, but the application of the term system is more reccent. Inspired in the work of Adam Smith, Milne-Edwards wrote that the body of all living beings, whether animal or plant, where the organs, comparable to workers, work incessantly to produce the phenomena that constitute the life of the individual. In more differentiated organisms, the labor could be apportioned between different instruments or systems. Synthesis and Analysis of a Biological System, by Hiroyuki Kurata,1999
Organ system
–
An example of a system: The
brain, the
cerebellum, the
spinal cord, and the
nerves are the four basic components of the
nervous system.
3.
Immune system
–
The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, a system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms. In many species, the system can be classified into subsystems, such as the innate immune system versus the adaptive immune system. In humans, the barrier, blood–cerebrospinal fluid barrier, and similar fluid–brain barriers separate the peripheral immune system from the neuroimmune system. Even simple unicellular organisms such as bacteria possess a rudimentary immune system in the form of enzymes that protect against bacteriophage infections, other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and invertebrates. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system, jawed vertebrates, including humans, have even more sophisticated defense mechanisms, including the ability to adapt over time to recognize specific pathogens more efficiently. Adaptive immunity creates immunological memory after a response to a specific pathogen. This process of acquired immunity is the basis of vaccination, disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer. Immunodeficiency occurs when the system is less active than normal. In humans, immunodeficiency can either be the result of a disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS. In contrast, autoimmunity results from an immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimotos thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, immunology covers the study of all aspects of the immune system. Immunology is a science that examines the structure and function of the immune system and it originates from medicine and early studies on the causes of immunity to disease. The earliest known reference to immunity was during the plague of Athens in 430 BC, thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without contracting the illness a second time. In the 18th century, Pierre-Louis Moreau de Maupertuis made experiments with scorpion venom and observed that certain dogs and this and other observations of acquired immunity were later exploited by Louis Pasteur in his development of vaccination and his proposed germ theory of disease. Pasteurs theory was in opposition to contemporary theories of disease. It was not until Robert Kochs 1891 proofs, for which he was awarded a Nobel Prize in 1905, viruses were confirmed as human pathogens in 1901, with the discovery of the yellow fever virus by Walter Reed. Immunology made an advance towards the end of the 19th century, through rapid developments, in the study of humoral immunity
Immune system
–
A
scanning electron microscope image of a single
neutrophil (yellow), engulfing
anthrax bacteria (orange)
Immune system
–
A
scanning electron microscope image of normal circulating human
blood. One can see
red blood cells, several knobby white blood cells including
lymphocytes, a
monocyte, a
neutrophil, and many small disc-shaped
platelets.
Immune system
–
An antibody is made up of two heavy chains and two light chains. The unique variable region allows an antibody to recognize its matching antigen.
Immune system
–
The time-course of an immune response begins with the initial pathogen encounter, (or initial vaccination) and leads to the formation and maintenance of active immunological memory.
4.
Lymphatic system
–
The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Unlike the cardiovascular system, the system is not a closed system. The human circulatory system processes an average of 20 liters of blood per day through capillary filtration, roughly 17 litres of the filtered plasma are reabsorbed directly into the blood vessels, while the remaining three litres remain in the interstitial fluid. One of the functions of the lymph system is to provide an accessory return route to the blood for the surplus three litres. The other main function is that of defense in the immune system, lymph is very similar to blood plasma, it contains lymphocytes and other white blood cells. It also contains waste products and cellular debris together with bacteria, associated organs composed of lymphoid tissue are the sites of lymphocyte production. Lymphocytes are concentrated in the lymph nodes, the spleen and the thymus are also lymphoid organs of the immune system. The tonsils are lymphoid organs that are associated with the digestive system. Lymphoid tissues contain lymphocytes, and also other types of cells for support. Lymph is the fluid that is formed when interstitial fluid enters the lymphatic vessels of the lymphatic system. Eventually, the lymph vessels empty into the ducts, which drain into one of the two subclavian veins, near their junction with the internal jugular veins. The lymphatic system consists of lymphatic organs, a network of lymphatic vessels. The primary or central lymphoid organs generate lymphocytes from immature progenitor cells, the thymus and the bone marrow constitute the primary lymphoid organs involved in the production and early clonal selection of lymphocyte tissues. Bone marrow is responsible for both the creation of T cells and the production and maturation of B cells, from the bone marrow, B cells immediately join the circulatory system and travel to secondary lymphoid organs in search of pathogens. T cells, on the hand, travel from the bone marrow to the thymus. Mature T cells join B cells in search of pathogens, the other 95% of T cells begin a process of apoptosis, a form of programmed cell death. Secondary or peripheral lymphoid organs, which include lymph nodes and the spleen, maintain mature naive lymphocytes, the peripheral lymphoid organs are the sites of lymphocyte activation by antigens. Activation leads to clonal expansion and affinity maturation, mature lymphocytes recirculate between the blood and the peripheral lymphoid organs until they encounter their specific antigen
Lymphatic system
–
Reed–Sternberg cells.
Lymphatic system
–
Human lymphatic system
Lymphatic system
–
"Claude Galien". Lithograph by Pierre Roche Vigneron. (Paris: Lith de Gregoire et Deneux, ca. 1865)
Lymphatic system
–
Gabriele Falloppio
5.
Latin
–
Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
Latin
–
Latin inscription, in the
Colosseum
Latin
–
Julius Caesar 's
Commentarii de Bello Gallico is one of the most famous classical Latin texts of the Golden Age of Latin. The unvarnished, journalistic style of this
patrician general has long been taught as a model of the urbane Latin officially spoken and written in the floruit of the
Roman republic.
Latin
–
A multi-volume Latin dictionary in the
University Library of Graz
Latin
–
Latin and Ancient Greek Language - Culture - Linguistics at
Duke University in 2014.
6.
Anatomical terminology
–
Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors. Anatomical terminology uses many terms, suffixes, and prefixes deriving from Ancient Greek. These terms can be confusing to those unfamiliar with them, but can be more precise reducing ambiguity, also, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted. By using precise anatomical terminology such ambiguity is eliminated, an international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the prefixes and suffixes are used to add meanings to different roots. The root of a term refers to an organ, tissue. For example, in the disorder hypertension, the prefix hyper- means high or over, the roots, prefixes and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants. Latin names of such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for two-headed. The first word tells us what we are speaking about, the second describes it, when describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, the cephalon or cephalic region refers to the head. This area is differentiated into the cranium, facies, frons, oculus, auris, bucca, nausus, oris. The neck area is called the cervicis or cervical region, examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body, for example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, similarly, in the arms, different terminology is often used in the arms, in part to reduce ambiguity as what is the front, back, inner and outer surfaces. For this reason, the terms below are used, Radial referring to the radius bone, ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet. International morphological terminology is used by the colleges of medicine and dentistry and it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research, teaching and medical care. The international morphological terminology refers to morphological sciences as a biological sciences branch, in this field, the form and structure are examined as well as the changes or developments in the organism
Anatomical terminology
–
The
anatomical position, with terms of relative location noted.
Anatomical terminology
–
The human body is shown in anatomical position in an anterior view and a posterior view. The regions of the body are labeled in boldface.
Anatomical terminology
–
Abdominal regions are used for example to localize pain.
7.
Oval
–
An oval is a closed curve in a plane which loosely resembles the outline of an egg. The term is not very specific, but in areas it is given a more precise definition. In common English, the term is used in a broader sense, the three-dimensional version of an oval is called an ovoid. The term oval when used to describe curves in geometry is not well-defined, many distinct curves are commonly called ovals or are said to have an oval shape. Generally, to be called an oval, a plane curve should resemble the outline of an egg or an ellipse, the adjectives ovoidal and ovate mean having the characteristic of being an ovoid, and are often used as synonyms for egg-shaped. In the theory of planes, an oval is a set of n +1 points in a projective plane of order n. An ovoid in the projective geometry PG is a set of q2 +1 points such that no three points are collinear. At each point of an all the tangent lines to the ovoid lie in a single plane. The shape of an egg is approximated by long half of a spheroid, joined to a short half of a roughly spherical ellipsoid. These are joined at the equator and sharing a principal axis of rotational symmetry, although the term egg-shaped usually implies a lack of reflection symmetry across the equatorial plane, it may also refer to true prolate ellipsoids. It can also be used to describe the 2-dimensional figure that, if revolved around its major axis, in technical drawing, an oval is a figure constructed from two pairs of arcs, with two different radii. The arcs are joined at a point in which lines tangential to both joining arcs lie on the line, thus making the joint smooth. Any point of an oval belongs to an arc with a constant radius, but in an ellipse, in common speech, oval means a shape rather like an egg or an ellipse, which may be two-dimensional or three-dimensional. It also often refers to a figure that resembles two semicircles joined by a rectangle, like a cricket infield, speed skating rink or an athletics track, however, this is more correctly called a stadium or archaically, an oblong. Sometimes, it can refer to any rectangle with rounded corners. The shape lends its name to many well-known places, ellipse Stadium Vesica piscis – a pointed oval
Oval
–
A chicken egg is a naturally occurring ovoid
Oval
–
This oval, with only one axis of symmetry, resembles a chicken egg.
8.
Organ (anatomy)
–
In biology, an organ or viscus is a collection of tissues joined in a structural unit to serve a common function. In anatomy, a viscus is an organ, and viscera is the plural form. Organs are composed of main tissue, parenchyma, and sporadic tissues, the main tissue is that which is unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, and connective tissues. The main tissues that make up an organ tend to have common embryologic origins, functionally related organs often cooperate to form whole organ systems. Organs exist in all biological organisms, in particular they are not restricted to animals. In single-cell organisms like bacteria, the analogue of an organ is called organelle. A hollow organ is an organ that forms a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity. Two or more organs working together in the execution of a specific body function form an organ system, the functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via an organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system, the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Mammals such as humans have a variety of organ systems and these specific systems are also widely studied in human anatomy. Cardiovascular system, pumping and channeling blood to and from the body and lungs with heart, digestive system, digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum and anus. Excretory system, kidneys, ureters, bladder and urethra involved in balance, electrolyte balance. Integumentary system, skin, hair and nails, nervous system, collecting, transferring and processing information with brain, spinal cord and nerves. Reproductive system, the sex organs, such as ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, prostate, respiratory system, the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm. Skeletal system, structural support and protection with bones, cartilage, ligaments, the organ level of organisation in animals can be first detected in flatworms and the more advanced phyla. The less-advanced taxa do not show consolidation of their tissues into organs, the study of plant organs is referred to as plant morphology, rather than anatomy, as in animal systems. Organs of plants can be divided into vegetative and reproductive, vegetative plant organs are roots, stems, and leaves
Organ (anatomy)
–
The
liver of a sheep. The liver is one of the main organs in the body.
Organ (anatomy)
–
The flower is the angiosperm's reproductive organ. This
Hibiscus flower is hermaphroditic, and it contains
stamen and
pistils.
Organ (anatomy)
–
Strobilus of
Equisetum telmateia.
Organ (anatomy)
–
Human viscera
9.
Adaptive immune system
–
The adaptive immune system is one of the two main immunity strategies found in vertebrates. Adaptive immunity creates immunological memory after a response to a specific pathogen. This process of acquired immunity is the basis of vaccination, like the innate system, the adaptive system includes both humoral immunity components and cell-mediated immunity components. Unlike the innate system, the adaptive immune system is highly specific to a particular pathogen. Adaptive immunity can also provide long-lasting protection, for example, someone who recovers from measles is now protected against measles for their lifetime, in other cases it does not provide lifetime protection, for example, chickenpox. The adaptive system response destroys invading pathogens and any toxic molecules they produce, sometimes the adaptive system is unable to distinguish harmful from harmless foreign molecules, the effects of this may be hayfever, asthma or any other allergy. Antigens are any substances that elicit the immune response. The cells that carry out the immune response are white blood cells known as lymphocytes. Two main broad classes—antibody responses and cell mediated immune response—are also carried by two different lymphocytes, in antibody responses, B cells are activated to secrete antibodies, which are proteins also known as immunoglobulins. Antibodies travel through the bloodstream and bind to the foreign antigen causing it to inactivate, in acquired immunity, pathogen-specific receptors are acquired during the lifetime of the organism. The acquired response is called adaptive because it prepares the immune system for future challenges. The system is highly adaptable because of somatic hypermutation, and VJ recombination and this mechanism allows a small number of genes to generate a vast number of different antigen receptors, which are then uniquely expressed on each individual lymphocyte. A theoretical framework explaining the workings of the immune system is provided by immune network theory. This theory, which builds on established concepts of clonal selection, is being applied in the search for an HIV vaccine, the major functions of the adaptive immune system include, Recognition of specific non-self antigens in the presence of self, during the process of antigen presentation. Generation of responses that are tailored to eliminate specific pathogens or pathogen-infected cells. Development of immunological memory, in which pathogens are remembered through memory B cells, the cells of the adaptive immune system are T and B lymphocytes, lymphocytes are a subset of leukocyte. B cells and T cells are the types of lymphocytes. The human body has about 2 trillion lymphocytes, constituting 20–40% of white blood cells, the peripheral blood contains 2% of circulating lymphocytes, the rest move within the tissues and lymphatic system
Adaptive immune system
–
A
scanning electron microscope (SEM) image of a single human
lymphocyte
10.
Lymphatic vessel
–
In anatomy, lymphatic vessels are thin-walled, valved structures that carry lymph. As part of the system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and have a layer of smooth muscles. Lymph vessels are devoted to propulsion of the lymph from the lymph capillaries, lymph capillaries are slightly larger than their counterpart capillaries of the vascular system. Lymph ducts drain the lymph into one of the subclavian veins, generally, lymph flows away from the tissues to lymph nodes and eventually to either the right lymphatic duct or the largest lymph vessel in the body, the thoracic duct. These vessels drain into the right and left subclavian veins respectively, the general structure of lymphatics is based on that of blood vessels. There is a lining of single flattened epithelial cells composed of a type of epithelium that is called endothelium. This layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous, the next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening or relaxing alter the diameter of the lumen. The outermost layer is the adventitia that consists of fibrous tissue, the general structure described here is seen only in larger lymphatics, smaller lymphatics have fewer layers. The smallest vessels lack both the muscular layer and the outer adventitia, as they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, and then smooth muscles. Unlike the cardiovascular system, the system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis, valves and these button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF, there is another system of semilunar valves that prevents back-flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections between them and form a fine network. Rhythmic contraction of the walls through movements may also help draw fluid into the smallest lymphatic vessels. If tissue fluid builds up the tissue will swell, this is called edema, the system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a circulatory system. The lymph capillaries drain the lymph to larger contractile lymphatics, which have valves as well as smooth muscle walls and these are called the collecting lymphatics
Lymphatic vessel
–
Lymph capillaries in the tissue spaces.
11.
B cell
–
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the immune system by secreting antibodies. Additionally, B cells present antigen and secrete cytokines, in mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors on their cell membrane. BCRs allow the B cell to bind a specific antigen, against which it will initiate an antibody response, B cells develop from hematopoietic stem cells that originate from bone marrow. HSCs first differentiate into multipotent progenitor cells, then common lymphoid progenitor cells, B cells undergo two types of selection while developing in the bone marrow to ensure proper development. Positive selection occurs through antigen-independent signaling involving both the pre-BCR and the BCR, if these receptors do not bind to their ligand, B cells do not receive the proper signals and cease to develop. This negative selection process leads to a state of central tolerance, to complete development, immature B cells migrate from the bone marrow to the spleen as well as pass through two transitional stages, T1 and T2. Throughout their migration to the spleen and after spleen entry, they are considered T1 B cells, within the spleen, T1 B cells transition to T2 B cells. T2 B cells differentiate into either follicular B cells or marginal zone B cells depending on signals received through the BCR, once differentiated, they are now considered mature B cells, or naive B cells. While immature and during the T1 phase, B cells express BCRCR of class IgH, B cell activation occurs in the secondary lymphoid organs, such as the spleen and lymph nodes. After B cells mature in the marrow, they migrate through the blood to SLOs. At the SLO, B cell activation begins when the B cell binds to an antigen via its BCR, antigen is presented to lymphocytes by APCs such as macrophages or dendritic cells, and include proteins, glycoproteins, polysaccharides, whole virus particles, and whole bacterial cells. Of the three B cell subsets, FO B cells preferentially undergo T cell-dependent activation while MZ B cells, B cell activation is enhanced through the activity of CD21, a surface receptor in complex with surface proteins CD19 and CD81. Antigens that activate B cells with the help of T-cell are known as T cell-dependent antigens and they are named as such because they are unable to induce a humoral response in organisms that lack T cells. B cell response to these antigens takes multiple days, though antibodies generated have an affinity and are more functionally versatile than those generated from T cell-independent activation. T helper cells, typically follicular T helper cells, that were activated with the same antigen recognize, following TCR-MHC-II-peptide binding, T cells express the surface protein CD40L as well as cytokines such as IL-4 and IL-21. T cell-derived cytokines bound by B cell cytokine receptors also promote B cell proliferation, immunoglobulin class switching, after B cells receive these signals, they are considered activated
B cell
12.
T cell
–
A T cell, or T lymphocyte, is a type of lymphocyte that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells and they are called T cells because they mature in the thymus from thymocytes. The several subsets of T cells each have a distinct function, the majority of human T cells rearrange their alpha and beta chains on the cell receptor and are termed alpha beta T cells and are part of the adaptive immune system. The category of effector T cell is a one that includes various T cell types that actively respond to a stimulus. This includes helper, killer, regulatory, and potentially other T cell types, T helper cells assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages. These cells are known as CD4+ T cells because they express the CD4 glycoprotein on their surfaces. Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response. These cells can differentiate one of several subtypes, including TH1, TH2, TH3, TH17, TH9, or TFH. Signalling from the APC directs T cells into particular subtypes, cytotoxic T cells destroy virus-infected cells and tumor cells, and are also implicated in transplant rejection. These cells are known as CD8+ T cells since they express the CD8 glycoprotein at their surfaces. These cells recognize their targets by binding to antigen associated with MHC class I molecules, through IL-10, adenosine, and other molecules secreted by regulatory T cells, the CD8+ cells can be inactivated to an anergic state, which prevents autoimmune diseases. Appropriate co-stimulation must be present at the time of encounter for this process to occur. Historically, memory T cells were thought to belong to either the effector or central memory subtypes, subsequently, numerous new populations of memory T cells were discovered including tissue-resident memory T cells, stem memory TSCM cells, and virtual memory T cells. The single unifying theme for all memory T cell subtypes is that they are long-lived, by this mechanism they provide the immune system with memory against previously encountered pathogens. Memory T cells may be either CD4+ or CD8+ and usually express CD45RO, memory T cell subtypes, Central memory T cells express CD45RO, C-C chemokine receptor type 7, and L-selectin. Central memory T cells also have intermediate to high expression of CD44 and this memory subpopulation is commonly found in the lymph nodes and in the peripheral circulation. Effector memory T cells express CD45RO but lack expression of CCR7 and they also have intermediate to high expression of CD44. These memory T cells lack lymph node-homing receptors and are found in the peripheral circulation
T cell
–
Scanning electron micrograph of a human T cell
T cell
–
Scanning electron micrograph of T lymphocyte (right), a
platelet (center) and a
red blood cell (left)
13.
Lymphocyte
–
A lymphocyte is one of the subtypes of white blood cell in a vertebrates immune system. Lymphocytes include natural killer cells, T cells, and B cells and they are the main type of cell found in lymph, which prompted the name lymphocyte. The three major types of lymphocyte are T cells, B cells and natural killer cells, lymphocytes can be identified by their large nucleus. T cells and B cells are the cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity, whereas B cells are responsible for humoral immunity. The function of T cells and B cells is to recognize specific “non-self” antigens, once they have identified an invader, the cells generate specific responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells. B cells respond to pathogens by producing large quantities of antibodies which then neutralize foreign objects like bacteria, following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. NK cells are a part of the immune system and play a major role in defending the host from both tumors and virally infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a molecule called MHC class I. NK cells are activated in response to a family of cytokines called interferons, activated NK cells release cytotoxic granules which then destroy the altered cells. They were named natural killer cells because of the notion that they do not require activation in order to kill cells which are missing MHC class I. This notion seemed doubtful at the time but turned out to be correct, mammalian stem cells differentiate into several kinds of blood cell within the bone marrow. All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types, the differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion. The formation of lymphocytes is known as lymphopoiesis, following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs where they survey for invading pathogens and/or tumor cells. The lymphocytes involved in adaptive immunity differentiate further after exposure to an antigen, they form effector, effector lymphocytes function to eliminate the antigen, either by releasing antibodies, cytotoxic granules or by signaling to other cells of the immune system. Microscopically, in a Wrights stained peripheral blood smear, a normal lymphocyte has a large, in normal situations, the coarse, dense nucleus of a lymphocyte is approximately the size of a red blood cell. Some lymphocytes show a clear perinuclear zone around the nucleus or could exhibit a clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope, the ribosomes are involved in protein synthesis, allowing the generation of large quantities of cytokines and immunoglobulins by these cells
Lymphocyte
–
A
scanning electron microscope (SEM) image of a single human lymphocyte.
Lymphocyte
–
A stained lymphocyte surrounded by
red blood cells viewed using a
light microscope.
Lymphocyte
–
A scanning electron microscope image of normal circulating human blood showing red blood cells, several types of white blood cells including lymphocytes, a
monocyte, a
neutrophil and many small disc-shaped platelets.
14.
White blood cell
–
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system, all white blood cells have nuclei, which distinguishes them from the other blood cells, the anucleated red blood cells and platelets. Types of white cells can be classified in standard ways. Two pairs of broadest categories classify them either by structure or by cell division lineage and these broadest categories can be further divided into the five main types, neutrophils, eosinophils, basophils, lymphocytes, and monocytes. These types are distinguished by their physical and functional characteristics, further subtypes can be classified, for example, among lymphocytes, there are B cells, T cells, and NK cells. The number of leukocytes in the blood is often an indicator of disease, the normal white cell count is usually between 4 × 109/L and 11 × 109/L. In the US this is expressed as 4,000 to 11,000 white blood cells per microliter of blood. They make up approximately 1% of the blood volume in a healthy adult. However, this 1% of the blood makes a difference to health. An increase in the number of leukocytes over the limits is called leukocytosis. It is normal when it is part of immune responses. It is occasionally abnormal, when it is neoplastic or autoimmune in origin, a decrease below the lower limit is called leukopenia. The name white blood cell derives from the appearance of a blood sample after centrifugation. White cells are found in the buff, a thin, typically white layer of nucleated cells between the red blood cells and the blood plasma. The scientific term leukocyte directly reflects its description and it is derived from the Greek roots leuk- meaning white and cyt- meaning cell. The buffy coat may sometimes be green if there are large amounts of neutrophils in the sample, all white blood cells are nucleated, which distinguishes them from the anucleated red blood cells and platelets. Types of leukocytes can be classified in standard ways, two pairs of broadest categories classify them either by structure or by cell lineage
White blood cell
–
A
scanning electron microscope image of normal circulating human blood. In addition to the irregularly shaped leukocytes, both
red blood cells and many small disc-shaped
platelets are visible.
White blood cell
–
Monocyte
White blood cell
–
Neutrophil engulfing
anthrax bacteria
15.
Inflamed
–
The classical signs of inflammation are heat, pain, redness, swelling, and loss of function. Inflammation is a response, and therefore it is considered as a mechanism of innate immunity, as compared to adaptive immunity. Too little inflammation could lead to tissue destruction by the harmful stimulus. In contrast, chronic inflammation may lead to a host of diseases, such as hay fever, periodontitis, atherosclerosis, rheumatoid arthritis, Inflammation is therefore normally closely regulated by the body. Inflammation can be classified as acute or chronic. Acute inflammation is the response of the body to harmful stimuli and is achieved by the increased movement of plasma. A series of biochemical events propagates and matures the inflammatory response, involving the vascular system, the immune system. Inflammation is not a synonym for infection, Inflammation on the other hand describes purely the bodys immunovascular response, whatever the cause may be. But because of how often the two are correlated, words ending in the suffix -itis are sometimes described as referring to infection. There are also situations where microbial invasion does not result in classic inflammatory response—for example, parasitosis. Acute inflammation is a process, usually appearing within a few minutes or hours. It involves a coordinated and systemic mobilisation response locally of various immune, endocrine, in a normal healthy response, it becomes activated, clears the pathogen and begins a repair process and then ceases. It is characterized by five signs, An acronym that may be used to remember the key symptoms is PRISH, for pain, redness, immobility, swelling. Loss of function has multiple causes, Acute inflammation of the lung does not cause pain unless the inflammation involves the parietal pleura, which does have pain-sensitive nerve endings. PAMPs are compounds that are associated with pathogens, but which are distinguishable from host molecules. DAMPs are compounds that are associated with host-related injury and cell damage, at the onset of an infection, burn, or other injuries, these cells undergo activation and release inflammatory mediators responsible for the clinical signs of inflammation. Vasodilation and its resulting increased blood flow causes the redness and increased heat, increased permeability of the blood vessels results in an exudation of plasma proteins and fluid into the tissue, which manifests itself as swelling. Some of the released mediators such as increase the sensitivity to pain
Inflamed
–
Toes inflamed by
chilblains
Inflamed
–
Infected
ingrown toenail showing the characteristic redness and swelling associated with acute inflammation
Inflamed
–
Micrograph showing granulation tissue.
H&E stain.
Inflamed
–
Scars present on the skin, evidence of fibrosis and healing of a wound
16.
Disease
–
A disease is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism. The study of disease is called pathology which includes the study of cause, Disease is often construed as a medical condition associated with specific symptoms and signs. When caused by pathogens, even in the literature, the term disease is often misleadingly used in the place of its causal agent. This language habitat can cause confusion in the communication of the principle in epidemiology. Diseases can affect not only physically, but also emotionally. Death due to disease is called death by natural causes, there are four main types of disease, infectious diseases, deficiency diseases, genetic diseases, and physiological diseases. Diseases can also be classified as communicable and non-communicable, the deadliest diseases in humans are coronary artery disease, followed by cerebrovascular disease and lower respiratory infections. In many cases, terms such as disease, disorder, morbidity, there are situations, however, when specific terms are considered preferable. Disease The term disease broadly refers to any condition that impairs the normal functioning of the body, for this reason, diseases are associated with dysfunctioning of the bodys normal homeostatic processes. The term disease has both a count sense and a noncount sense, by contrast, an infection that is asymptomatic during its incubation period, but expected to produce symptoms later, is usually considered a disease. Non-infectious diseases are all other diseases, including most forms of cancer, heart disease, acquired disease disease that began at some point during ones lifetime, as opposed to disease that was already present at birth, which is congenital disease. Acquired sounds like it could mean caught via contagion, but it simply means acquired sometime after birth and it also sounds like it could imply secondary disease, but acquired disease can be primary disease. It is often, genetic and can be inherited and it can also be the result of a vertically transmitted infection from the mother such as HIV/AIDS. Genetic disease disease that is caused by genetic mutation and it is often inherited, but some mutations are random and de novo. Hereditary or inherited disease a type of disease caused by mutation that is hereditary Iatrogenic disease A disease condition caused by medical intervention. Idiopathic disease disease whose cause is unknown, as medical science has advanced, many diseases whose causes were formerly complete mysteries have been somewhat explained or even extensively explained. Bacterial infections can be primary or secondary to a viral infection or burn. Terminal disease disease with death as an inevitable result Illness Illness is generally used as a synonym for disease, however, this term is occasionally used to refer specifically to the patients personal experience of his or her disease
Disease
–
Scanning electron micrograph of
Mycobacterium tuberculosis, a
bacterium that causes
tuberculosis.
Disease
–
Obesity was a status symbol in
Renaissance culture: "The Tuscan General
Alessandro del Borro ", attributed to
Andrea Sacchi, 1645. It is now generally regarded as a disease.
17.
Lymph node capsule
–
A lymph node or lymph gland, is an ovoid or kidney-shaped organ of the lymphatic system, and of the adaptive immune system, that is widely present throughout the body. They are linked by the vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a function, which is primarily dealt with by the liver. In the lymphatic system the lymph node is a secondary lymphoid organ, a lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla. Lymph nodes also have clinical significance and they become inflamed or enlarged in various diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the nodes is very important in cancer staging, which decides the treatment to be used. When swollen, inflamed or enlarged, lymph nodes can be hard, Lymph nodes are kidney or oval shaped and range in size from a few millimeters to about 1–2 cm long. Each lymph node is surrounded by a capsule, which extends inside the lymph node to form trabeculae. The substance of the node is divided into the outer cortex. The cortex is continuous around the medulla except where the medulla comes into contact with the hilum. Thin reticular fibers of reticular connective tissue, and elastin form a supporting meshwork called a reticulin inside the node, B cells, are mainly found in the outer where they are clustered together as follicular B cells in lymphoid follicles and the T cells are mainly in the paracortex. The number and composition of follicles can change especially when challenged by an antigen, elsewhere in the node, there are only occasional leucocytes. As part of the network there are follicular dendritic cells in the B cell follicle. The reticular network not only provides the support, but also the surface for adhesion of the dendritic cells. It allows exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses and these vessels are smaller and dont allow the passage of the macrophages so that they remain contained to function within the lymph node. In the course of the lymph, lymphocytes may be activated as part of the immune response
Lymph node capsule
–
1) Capsule; 2) Subcapsular sinus; 3) Germinal centre; 4) Lymphoid nodule; 5) Trabeculae
Lymph node capsule
–
Diagram of a lymph node, showing the flow of lymph through the
lymph sinuses.
Lymph node capsule
–
Lymph node histology
Lymph node capsule
–
There are clusters of nodes under the arms, in the groin, neck and abdomen
18.
Cortex (anatomy)
–
In anatomy and zoology, the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex and these sensory areas receive and process information from the senses. The senses of vision, audition, and touch are served by the visual cortex, primary auditory cortex. The cortex is the surface of the cerebrum and is composed of gray matter. The motor areas are located in both hemispheres of the cerebral cortex
Cortex (anatomy)
–
The cerebral cortex, in this case of a
rhesus macaque monkey, is the outer layer depicted in dark violet.
Cortex (anatomy)
–
The renal cortex, here denoted by the number 2.
19.
Reticular fiber
–
Reticular fibers, reticular fibres or reticulin is a type of fiber in connective tissue composed of type III collagen secreted by reticular cells. Reticular fibers crosslink to form a fine meshwork and this network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system. The term reticulin was coined in 1892 by M. Siegfried, today, the term reticulin or reticular fiber is restricted to referring to fibers composed of type III collagen. The history of the silver stain is reviewed by Puchtler et al. The abstract of this says, Maresch introduced Bielschowskys silver impregnation technic for neurofibrils as a stain for reticulum fibers. This lack of specificity has been confirmed repeatedly, yet, since the 1920s the definition of reticulin and studies of its distribution were based solely on silver impregnation technics. The chemical mechanism and specificity of this group of stains is obscure, application of Gömöris and Wilders methods to human tissues showed variations of staining patterns with the fixatives and technics employed. Besides reticulum fibers, various other structures, e. g. I bands of striated muscle, fibers in nervous tissues, and model substances, e. g. polysaccharides, egg white, deposition of silver compounds on reticulum fibers was limited to an easily removable substance, the remaining collagen component did not bind silver. Reticular fiber is composed of one or more types of very thin and these strands build a highly ordered cellular network and provide a supporting network. Many of these types of collagen have been combined with carbohydrate, thus, they react with silver stains and with periodic acid-Schiff reagent but are not demonstrated with ordinary histological stains such as those using hematoxylin. In a 1993 paper, the fibers of the capillary sheath. This paper attempted to reveal their components and the presence of acid in the amorphous ground substance. Collagen fibrils, elastic fibers, microfibrils, nerve fibers, on the other hand, only microfibrils were recognized in the reticular fibers of the capillary sheath. The binding of LFA lectin to the cord was stronger than the capillary sheath. These findings suggested that the fibers of the splenic cord include multiple functional elements. On the other hand, the fiber of the capillary sheath resembled the basement membrane of the capillary in its components. Because of their affinity for silver salts, these fibers are called argyrophilic, reticulin at the US National Library of Medicine Medical Subject Headings MedEd at Loyola Histo/practical/stains/hp2-55. html
Reticular fiber
–
A
liver biopsy stained with a
reticulin stain demonstrating a normal hepatic plate thickness and mild
steatosis.
20.
Antigen
–
In immunology, an antigen is a molecule capable of inducing an immune response on the part of the host organism, though sometimes antigens can be part of the host itself. In other words, an antigen is any substance that causes a system to produce antibodies against it. In most cases, an antibody can bind one specific antigen, in some instances, however. An antigen is a molecule that binds to Ag-specific receptors, Antigens are usually peptides, polysaccharides or lipids. In general, molecules other than peptides qualify as antigens but not as immunogens since they cannot elicit a response on their own. Furthermore, for a peptide to induce a response it must be a large enough size. The term antigen originally described a structural molecule that specifically to an antibody. It expanded to refer to any molecule or a molecular fragment that can be recognized by highly variable antigen receptors of the adaptive immune system. The antigen may originate from within the body or from the external environment, antigen presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cells of the immune system recognize the antigens. Depending on the antigen and the type of the histocompatibility molecule, for T-Cell Receptor recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex. The antigen cannot elicit the immune response without the help of an immunologic adjuvant, similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system. An immunogen is a substance that is able to trigger a humoral and/or cell-mediated immune response and it first initiates an innate immune response, which then causes the activation of the adaptive immune response. An antigen binds the highly variable immunoreceptor products once these have been generated, all immunogen molecules are also antigens, although the reverse is not true. At the molecular level, an antigen can be characterized by its ability to bind to an antibodys variable Fab region, different antibodies have the potential to discriminate among specific epitopes present on the antigen surface. A hapten is a molecule that changes the structure of an antigenic epitope. In order to induce a response, it needs to be attached to a large carrier molecule such as a protein. Antigens are usually proteins and polysaccharides, and less frequently, lipids and this includes parts of bacteria, viruses, and other microorganisms
Antigen
–
Contents
21.
Germinal center
–
They develop dynamically after the activation of follicular B cells by T-dependent antigen. As they undergo rapid and mutative cellular division in the dark zone, histologically, the GCs describe microscopically distinguishable parts in lymphoid tissues. During TFH-B cell conjugation, the B cell receives critical signals to undergo isotype switching, during this time they are referred to as centroblasts and make up the dark zone. This involves pseudo-random substitutions biased towards regions encoding the antigen recognition surface of the antibodies the B cells produce and this phenomenon underscores the process of affinity maturation, whereby greater affinity antibodies are produced and selected for after antigen recognition. The centrocytes are in a state of activated apoptosis and compete for survival signals derived from follicular dendritic cell and this rescue process, known as germinal center selection, is believed to be dependent on the affinity of their surface antibody to the antigen. Cyclic re-entry into the dark once again as centroblasts allows a chance for otherwise non-selected B cell mutants to gain more mutations in order to improve affinity towards antigen. Interactions with T cells are believed to prevent the generation of autoreactive germinal center B cells. Selected B cells may also restart the cycle of mutative centroblast division. In this way the immune system, in part through these germinal center reactions. The morphology of GCs is very specific and shows properties which are characteristic for different stages of the reaction, in an early state of the reaction a network of FDCs is fully filled with proliferating B cells. Later at day 4 of the reaction, GCs show a separation of two zones, the dark and the light zone, the former still contains dominantly proliferating and mutating B cells while the latter one is the area of B cell selection. These zones dissolve after 10 days of GC development which ends after about 3 weeks. html
Germinal center
–
Germinal center of a lymph node showing proliferation and development stages of a B cell.
22.
Fibroblastic
–
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals, fibroblasts and fibrocytes are two states of the same cells, the former being the activated state, the latter the less active state, concerned with maintenance and tissue metabolism. Currently, there is a tendency to both forms fibroblasts. The suffix -blast is used in biology to denote a stem cell or a cell in an activated state of metabolism. Fibroblasts are morphologically heterogeneous with diverse appearances depending on their location and this remarkable behavior may lead to discomfort in the rare event that they stagnate there excessively. The main function of fibroblasts is to maintain the integrity of connective tissues by continuously secreting precursors of the extracellular matrix. Fibroblasts secrete the precursors of all the components of the matrix, primarily the ground substance. The composition of the extracellular matrix determines the properties of connective tissues. Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme, thus they express the intermediate filament protein vimentin, a feature used as a marker to distinguish their mesodermal origin. However, this test is not specific as epithelial cells cultured in vitro on adherent substratum may also express vimentin after some time, in certain situations epithelial cells can give rise to fibroblasts, a process called epithelial-mesenchymal transition. This process is seen in many situations, as well as in wound healing. Fibroblasts have a branched cytoplasm surrounding an elliptical, speckled nucleus having two or more nucleoli, active fibroblasts can be recognized by their abundant rough endoplasmic reticulum. Inactive fibrocytes are smaller, spindle shaped, and have a reduced rough endoplasmic reticulum, although disjointed and scattered when they have to cover a large space, fibroblasts, when crowded, often locally align in parallel clusters. Fibroblasts make collagens, glycosaminoglycans, reticular and elastic fibers, glycoproteins found in the extracellular matrix, growing individuals fibroblasts are dividing and synthesizing ground substance. Tissue damage stimulates fibrocytes and induces the mitosis of fibroblasts, fibroblasts can also migrate slowly over substratum as individual cells, again in contrast to epithelial cells. While epithelial cells form the lining of body structures, it is fibroblasts, the life span of a fibroblast, as measured in chick embryos, is 57 ±3 days. Besides their commonly known role as components, fibroblasts play a critical role in an immune response to a tissue injury. They are early players in initiating inflammation in the presence of invading microorganisms and they induce chemokine synthesis through the presentation of receptors on their surface
Fibroblastic
–
NIH/3T3 Fibroblasts in
cell culture
Fibroblastic
–
Microfilaments, mitochondria, and nuclei in fibroblast cells
23.
Dendritic cell
–
Dendritic cells are antigen-presenting cells of the mammalian immune system. Their main function is to process antigen material and present it on the surface to the T cells of the immune system. They act as messengers between the innate and the immune systems. Dendritic cells are present in tissues that are in contact with the external environment, such as the skin. They can also be found in a state in the blood. Once activated, they migrate to the nodes where they interact with T cells and B cells to initiate. At certain development stages they grow branched projections, the dendrites that give the cell its name, while similar in appearance, these are structures distinct from the dendrites of neurons. Immature dendritic cells are also called veiled cells, as they possess large cytoplasmic veils rather than dendrites, dendritic cells were first described by Paul Langerhans in the late nineteenth century. The term dendritic cells was coined in 1973 by Ralph M. Steinman, the morphology of dendritic cells results in a very large surface-to-volume ratio. That is, the cell has a very large surface area compared to the overall cell volume. The most common division of cells is myeloid vs. plasmacytoid, The markers BDCA-2, BDCA-3. Lymphoid and myeloid DCs evolve from lymphoid and myeloid precursors, respectively, the blood DCs are typically identified and enumerated in flow cytometry. Three types of DCs have been defined in human blood, the CD1c+ myeloid DCs, the CD141+ myeloid DCs and this represents the nomenclature proposed by the nomenclature committee of the International Union of Immunological Societies. Dendritic cells that circulate in blood do not have all the features of their counterparts in tissue. Still, they can perform functions including chemokine-production, cross-presentation. In some respects, dendritic cells cultured in vitro do not show the behaviour or capability as dendritic cells isolated ex vivo. Nonetheless, they are used for research as they are still much more readily available than genuine DCs. Mo-DC or MDDC refers to cells matured from monocytes HP-DC refers to cells derived from hematopoietic progenitor cells, while humans and non-human primates such as rhesus macaques appear to have DCs divided into these groups, other species have different subdivisions of DCs
Dendritic cell
–
Dendritic cells in skin
Dendritic cell
Dendritic cell
–
A dendritic cell
24.
Macrophage
–
These large phagocytes are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms throughout the body, but all are part of the mononuclear phagocyte system, besides phagocytosis, they play a critical role in nonspecific defense and also help initiate specific defense mechanisms by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells, in humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections. Beyond increasing inflammation and stimulating the system, macrophages also play an important anti-inflammatory role. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation, human macrophages are about 21 micrometres in diameter and are produced by the differentiation of monocytes in tissues. They can be identified using flow cytometry or immunohistochemical staining by their expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 /EMR1, lysozyme M, MAC-1/MAC-3. Macrophages were first discovered by Élie Metchnikoff, a Russian zoologist, when a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as the leukocyte extravasation, it undergoes a series of changes to become a macrophage. At some sites such as the testis, macrophages have shown to populate the organ through proliferation. Unlike short-lived neutrophils, macrophages survive longer in the body up to a maximum of several months, macrophages are professional phagocytes and are highly specialized in removal of dying or dead cells and cellular debris. This role is important in inflammation, as the early stages of inflammation are dominated by neutrophils. The neutrophils are at first attracted to a site, where they proliferate, when a macrophage ingests a pathogen, the pathogen becomes trapped in a phagosome, which then fuses with a lysosome. Within the phagolysosome, enzymes and toxic peroxides digest the pathogen, however, some bacteria, such as Mycobacterium tuberculosis, have become resistant to these methods of digestion. Typhoidal Salmonellae too induce their own phagocytosis by host macrophages in vivo, macrophages can digest more than 100 bacteria before they finally die due to their own digestive compounds. Macrophages are versatile cells that play many roles, as scavengers, they rid the body of worn-out cells and other debris. Along with dendritic cells, they are foremost among the cells present antigens. At the same time, they carry receptors for lymphokines that allow them to be activated into single-minded pursuit of microbes, after digesting a pathogen, a macrophage will present the antigen of the pathogen to the corresponding helper T cell. In some cases, pathogens are very resistant to adhesion by the macrophages, the antigen presentation on the surface of infected macrophages in a lymph node stimulates TH1 to proliferate. When a B-cell in the lymph node recognizes the same unprocessed surface antigen on the bacterium with its surface bound antibody, the processed antigen is then presented in MHCII on the surface of the B-cell
Macrophage
–
A macrophage of a
mouse stretching its "arms" (
pseudopodia) to engulf two particles, possibly
pathogens.
Trypan Blue Exclusion.
25.
Dense irregular connective tissue
–
Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue. This tissue comprises a portion of the dermis. This type of tissue is also in the Sclera and in the skin layers. It also makes up submucosa of the tract, fibrous capsules of joints and lymph nodes. Other examples include periosteum and perichondrium and tunica albugenia, dense irregular tissues have fibroblasts and matrix fibers that are oriented differently, i. e. not oriented in a parallel fashion. This tissue is present in the skin and it consists primarily of collagenous fibers, but fibroblasts and ground substance are also present
Dense irregular connective tissue
–
Illustration of Dense Irregular Connective Tissue (Deep Dermis)
26.
Collagen
–
Collagen /ˈkɒlədʒᵻn/ is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of tissue, it is the most abundant protein in mammals. Depending upon the degree of mineralization, collagen tissues may be rigid, compliant, Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs, in muscle tissue, it serves as a major component of the endomysium. Collagen constitutes one to two percent of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles, the fibroblast is the most common cell that creates collagen. Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed, Collagen also has many medical uses in treating complications of the bones and skin. The name collagen comes from the Greek κόλλα, meaning glue and this refers to the compounds early use in the process of boiling the skin and sinews of horses and other animals to obtain glue. Collagen occurs in places throughout the body. Over 90% of the collagen in the body, however, is type I. So far,28 types of collagen have been identified and described, type IV, forms basal lamina, the epithelium-secreted layer of the basement membrane. Type V, cell surfaces, hair and placenta The collagenous cardiac skeleton which includes the four valve rings, is histologically, elastically and uniquely bound to cardiac muscle. The cardiac skeleton also includes the separating septa of the heart chambers – the interventricular septum, Collagen contribution to the measure of cardiac performance summarily represents a continuous torsional force opposed to the fluid mechanics of blood pressure emitted from the heart. With support from collagen, atrial fibrillation should never deteriorate to ventricular fibrillation, Collagen is layered in variable densities with cardiac muscle mass. The mass, distribution, age and density of collagen all contribute to the required to move blood back. Individual cardiac valvular leaflets are folded into shape by specialized collagen under variable pressure, gradual calcium deposition within collagen occurs as a natural function of aging. Pathology of the underpinning of the heart is understood within the category of connective tissue disease. Collagen has been used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone and a wide variety of dental, orthopedic. Both human and bovine collagen is used as dermal fillers for treatment of wrinkles
Collagen
–
Collagen triple helix
Collagen
–
Action of
lysyl oxidase
27.
Lymphatic fluid
–
Lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the fluid is collected through lymph capillaries. Since the lymph is derived from the fluid, its composition continually changes as the blood. It is generally similar to blood plasma except that it doesnt contain red blood cells, lymph returns proteins and excess interstitial fluid to the bloodstream. Lymph may pick up bacteria and bring them to lymph nodes, metastatic cancer cells can also be transported via lymph. Lymph also transports fats from the system to the blood via chylomicrons. The word lymph is derived from the name of the ancient Roman deity of fresh water, lymph has a composition comparable to that of blood plasma, but it may differ slightly. In particular, the lymph that leaves a lymph node is richer in lymphocytes, likewise, the lymph formed in the human digestive system called chyle is rich in triglycerides, and looks milky white because of its lipid content. As the blood and the surrounding cells continually add and remove substances from the interstitial fluid, thus, lymph when formed is a watery clear liquid with the same composition as the interstitial fluid. However, as it flows through the nodes it comes in contact with blood. Tubular vessels transport lymph back to the blood, ultimately replacing the volume lost during the formation of the interstitial fluid and these channels are the lymphatic channels, or simply lymphatics. Unlike the cardiovascular system, the system is not closed and has no central pump. Lymph transport, therefore, is slow and sporadic, despite low pressure, lymph movement occurs due to peristalsis, valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation. Lymph that enters the lymph vessels from the interstitial spaces usually does not flow backwards along the vessels because of the presence of valves. If excessive hydrostatic pressure develops within the vessels, though, some fluid can leak back into the interstitial spaces. Flow of the lymph in the duct in an average resting person usually approximates 100ml per hour. Accompanied by another ~25ml per hour in other vessels, total lymph flow in the body is about 4 to 5 liters per day. Which can be elevated several folds in case of exercising, thus it can be estimated that without lymphatic flow, an average resting person would die within 24 hours
Lymphatic fluid
–
Human lymph, obtained after a thoracic duct injury
Lymphatic fluid
–
Diagram showing the formation of lymph from
interstitial fluid (labeled here as "Tissue fluid"). Note how the tissue fluid is entering the blind ends of
lymph capillaries (shown as deep green arrows)
Lymphatic fluid
–
Formation of interstitial fluid from blood
28.
Fibroblast
–
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals, fibroblasts and fibrocytes are two states of the same cells, the former being the activated state, the latter the less active state, concerned with maintenance and tissue metabolism. Currently, there is a tendency to both forms fibroblasts. The suffix -blast is used in biology to denote a stem cell or a cell in an activated state of metabolism. Fibroblasts are morphologically heterogeneous with diverse appearances depending on their location and this remarkable behavior may lead to discomfort in the rare event that they stagnate there excessively. The main function of fibroblasts is to maintain the integrity of connective tissues by continuously secreting precursors of the extracellular matrix. Fibroblasts secrete the precursors of all the components of the matrix, primarily the ground substance. The composition of the extracellular matrix determines the properties of connective tissues. Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme, thus they express the intermediate filament protein vimentin, a feature used as a marker to distinguish their mesodermal origin. However, this test is not specific as epithelial cells cultured in vitro on adherent substratum may also express vimentin after some time, in certain situations epithelial cells can give rise to fibroblasts, a process called epithelial-mesenchymal transition. This process is seen in many situations, as well as in wound healing. Fibroblasts have a branched cytoplasm surrounding an elliptical, speckled nucleus having two or more nucleoli, active fibroblasts can be recognized by their abundant rough endoplasmic reticulum. Inactive fibrocytes are smaller, spindle shaped, and have a reduced rough endoplasmic reticulum, although disjointed and scattered when they have to cover a large space, fibroblasts, when crowded, often locally align in parallel clusters. Fibroblasts make collagens, glycosaminoglycans, reticular and elastic fibers, glycoproteins found in the extracellular matrix, growing individuals fibroblasts are dividing and synthesizing ground substance. Tissue damage stimulates fibrocytes and induces the mitosis of fibroblasts, fibroblasts can also migrate slowly over substratum as individual cells, again in contrast to epithelial cells. While epithelial cells form the lining of body structures, it is fibroblasts, the life span of a fibroblast, as measured in chick embryos, is 57 ±3 days. Besides their commonly known role as components, fibroblasts play a critical role in an immune response to a tissue injury. They are early players in initiating inflammation in the presence of invading microorganisms and they induce chemokine synthesis through the presentation of receptors on their surface
Fibroblast
–
NIH/3T3 Fibroblasts in
cell culture
Fibroblast
–
Microfilaments, mitochondria, and nuclei in fibroblast cells
29.
Plasma cell
–
Plasma cells, also called plasma B cells, plasmocytes, plasmacytes, or effector B cells, are white blood cells that secrete large volumes of antibodies. They are transported by the plasma and the lymphatic system. Plasma cells originate in the marrow, B cells differentiate into plasma cells that produce antibody molecules closely modeled after the receptors of the precursor B cell. Once released into the blood and lymph, these molecules bind to the target antigen. After leaving the bone marrow, the B cell acts as an antigen presenting cell and internalizes offending antigens, pieces of the antigen are loaded onto MHC II molecules, and presented on its extracellular surface to CD4+ T cells. These T cells bind to the MHC II-antigen molecule and cause activation of the B cell and this is a type of safeguard to the system, almost like a two-factor authentication method. First, the B cells have to encounter a foreign antigen, germinal center B cells may differentiate into memory B cells or plasma cells. Most of these B cells will become plasmablasts, and eventually plasma cells, some B cells will undergo a process known as affinity maturation. This process favors, by selection for the ability to bind antigen with higher affinity, the most immature blood cell that is considered of plasma cell lineage is the plasmablast. Plasmablasts secrete more antibodies than B cells, but less than plasma cells and they divide rapidly and are still capable of internalizing antigens and presenting them to T cells. A cell may stay in state for several days, and then either die or irrevocably differentiate into a mature. Differentiation of mature B cells into cells is dependent upon the transcription factors Blimp-1/PRDM1. After the process of affinity maturation in germinal centers, plasma cells have an indeterminate lifespan, recently they have been shown to reside for much longer periods in the bone marrow as long-lived plasma cells. They secrete high levels of antibodies, ranging from hundreds to thousands of antibodies per second per cell, however, continued exposure to antigen through those low levels of immunoglobulin is important, as it partly determines the cells lifespan. The lifespan, class of antibodies produced, and the location that the cell moves to also depends on signals, such as cytokines. Differentiation through a T cell-independent antigen stimulation can happen anywhere in the body, for example, plasma cells will likely secrete IgG3 antibodies if they matured in the presence of the cytokine interferon-gamma. Since B cell maturation also involves somatic hypermutation, these antibodies frequently have a high affinity for their antigen. Plasma cells can produce a single kind of antibody in a single class of immunoglobulin
Plasma cell
–
Malignant plasma cells (
plasmacytoma), with the characteristic "clockface nuclei" seen in normal plasma cells.
H&E stain.
Plasma cell
–
Plasma cell with distinct clear perinuclear region of the cytoplasm containing a large number of
Golgi bodies.
Plasma cell
–
Plasma cells with Dutcher and Russell bodies (H&E, 100x, oil)
30.
Groin
–
In human anatomy, the groin is the junctional area between the abdomen and the thigh on either side of the pubic bone. This is also known as the compartment of the thigh that consists of the adductor muscles of the hip or the groin muscles. A pulled groin muscle usually refers to an injury sustained by straining the hip adductor muscles. These hip adductor muscles that make up the groin consist of the adductor brevis, adductor longus, adductor magnus, gracilis and these groin muscles adduct the thigh. In the groin, underneath the skin, there are three to five deep inguinal lymph nodes that play a role in the immune system and these can be swollen due to certain diseases, the most common one being a simple infection, and, less likely, from cancer. A chain of superficial inguinal lymph nodes drain to the deep nodes, in a venography procedure, the groin is the preferred site for incisions to enter a catheter into the vascular system. The inguinal ligament runs from the pubic tubercle to the superior iliac spine. Groin is sometimes used as a euphemism for the reproductive organs, in a venography procedure, the groin is the preferred site for incisions to enter a catheter into the vascular system
Groin
–
Areas of the groin (3) marks the inguinal canal
31.
Abdomen
–
The abdomen constitutes the part of the body between the thorax and pelvis, in humans and in other vertebrates. The region occupied by the abdomen is termed the abdominal cavity, in arthropods it is the posterior tagma of the body, it follows the thorax or cephalothorax. The abdomen stretches from the thorax at the diaphragm to the pelvis at the pelvic brim. The pelvic brim stretches from the joint to the pubic symphysis and is the edge of the pelvic inlet. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity, the boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear. The abdomen contains most of the organs of the digestive tract. Hollow abdominal organs include the stomach, the intestine. Organs such as the liver, its attached gallbladder, and the function in close association with the digestive tract. The spleen, kidneys, and adrenal glands also lie within the abdomen, along with blood vessels including the aorta. Anatomists may consider the urinary bladder, uterus, fallopian tubes, finally, the abdomen contains an extensive membrane called the peritoneum. A fold of peritoneum may completely cover certain organs, whereas it may only one side of organs that usually lie closer to the abdominal wall. Anatomists call the type of organs retroperitoneal. For example, the stomach of ruminants is divided into four chambers – rumen, in vertebrates, the abdomen is a large cavity enclosed by the abdominal muscles, ventrally and laterally, and by the vertebral column dorsally. Lower ribs can also enclose ventral and lateral walls, the abdominal cavity is upper part of the pelvic cavity. It is attached to the cavity by the diaphragm. Structures such as the aorta, inferior vena cava and esophagus pass through the diaphragm, both the abdominal and pelvic cavities are lined by a serous membrane known as the parietal peritoneum. This membrane is continuous with the visceral peritoneum lining the organs, the abdomen in vertebrates contains a number of organs belonging, for instance, to the digestive tract and urinary system. There are three layers of the abdominal wall and they are, from the outside to the inside, external oblique, internal oblique, and transverse abdominal
Abdomen
–
The human abdomen and organs which can be found beneath the surface
Abdomen
–
(left) Henry Gray (1825–1861). Anatomy of the Human Body. (Right) A modern example of a human
male abdomen above
Abdomen
–
The analogous gross morphologies of a human and an ant
32.
Anatomy
–
Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is inherently tied to embryology, comparative anatomy, evolutionary biology, Human anatomy is one of the basic essential sciences of medicine. The discipline of anatomy is divided into macroscopic and microscopic anatomy, macroscopic anatomy, or gross anatomy, is the examination of an animals body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy, microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, and also in the study of cells. The history of anatomy is characterized by an understanding of the functions of the organs. Anatomy and physiology, which study the structure and function of organisms and their parts, make a pair of related disciplines. Derived from the Greek ἀνατομή anatomē dissection, anatomy is the study of the structure of organisms including their systems, organs. It includes the appearance and position of the parts, the materials from which they are composed, their locations. Anatomy is quite distinct from physiology and biochemistry, which deal respectively with the functions of those parts, the discipline of anatomy can be subdivided into a number of branches including gross or macroscopic anatomy and microscopic anatomy. Gross anatomy is the study of large enough to be seen with the naked eye, and also includes superficial anatomy or surface anatomy. Microscopic anatomy is the study of structures on a scale, including histology. Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs, angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels. The term anatomy is commonly taken to refer to human anatomy, however, substantially the same structures and tissues are found throughout the rest of the animal kingdom and the term also includes the anatomy of other animals. The term zootomy is also used to specifically refer to animals. The structure and tissues of plants are of a dissimilar nature, the kingdom Animalia or metazoa, contains multicellular organisms that are heterotrophic and motile. Most animals have bodies differentiated into separate tissues and these animals are known as eumetazoans. They have a digestive chamber, with one or two openings, the gametes are produced in multicellular sex organs, and the zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells, unlike plant cells, animal cells have neither a cell wall nor chloroplasts
Anatomy
–
One of the large, detailed illustrations in
Andreas Vesalius 's
De humani corporis fabrica 16th century, marking the rebirth of anatomy
Anatomy
–
Human compared to elephant frame.
Benjamin Waterhouse Hawkins, 1860
Anatomy
–
Hyaline cartilage at high magnification (
H&E stain)
Anatomy
–
Gastric mucosa at low magnification (
H&E stain)
33.
Axillary lymph nodes
–
They are divided in several groups according to their location in the armpit. These lymph nodes are clinically significant in breast cancer, and metastases from the breast to the lymph nodes are considered in the staging of the disease. Posterior group, Lying in front of the muscle, these nodes receive superficial lymph vessels from the back. Lateral group, Lying along the side of the axillary vein. Central group, Lying in the center of the axilla in the axillary fat, infraclavicular group, These nodes are not strictly axillary nodes because they are located outside the axilla. They lie in the groove between the deltoid and pectoralis major muscles and receive superficial lymph vessels from the side of the hand, forearm. Apical group, Lying at the apex of the axilla at the border of the 1st rib. The apical nodes drain into the subclavian lymph trunk, on the left side, this trunk drains into the thoracic duct, on the right side, it drains into the right lymphatic duct. Alternatively, the trunks may drain directly into one of the large veins at the root of the neck. About 75% of lymph from the drains into the axillary lymph nodes. A doctor will usually refer a patient to a surgeon to have an axillary lymph node dissection to see if the cells have been trapped in the nodes. For clinical stages I and II breast cancer, axillary lymph node dissection should only be performed after first attempting sentinel node biopsy, if cancer cells are found in the nodes it increases the risk of metastatic breast cancer. Another method of determining breast cancer spread is to perform an endoscopic axillary sentinel node biopsy and this involves injecting a dye into the breast lump and seeing which node it first spread to. This node is removed and examined. If there is no cancer present, it is assumed the cancer has not spread to the lymph nodes. This procedure is less invasive and less damaging than the axillary lymph node dissection. The estimated risk of lymphedema following sentinel lymph node procedure is less than 3%, axillary lymph nodes are included within the standard tangential fields in radiotherapy for breast cancer. In the case of comprehensive nodal irradiation, which includes axillary levels I, II, the risk is estimated to be less than 5% as the brachial plexus radiation tolerance according to is 60 Gy in standard fractionation
Axillary lymph nodes
–
2. Axillary lymphatic plexus 4. Cubital lymph nodes (not part of the lymph node drainage of the breast) 5. Superficial axillary (low axillary) 6. Deep axillary lymph nodes 7. Brachial axillary lymph nodes 8. Interpectoral axillary lymph nodes (Rotter nodes) 10. Paramammary or intramammary lymph nodes 11. Parasternal lymph nodes (internal mammary nodes)
Axillary lymph nodes
–
Lymphatics of the breast and the axillary glands
Axillary lymph nodes
–
Lymph nodes of the upper limb and breast
34.
Cervical lymph nodes
–
Cervical lymph nodes are lymph nodes found in the neck. Of the 800 lymph nodes in the body,300 are in the neck. Cervical lymph nodes are subject to a number of different pathological conditions including tumours, there are approximately 300 lymph nodes in the neck, and they can be classified in many different ways. Commonly used systems have been devised by the American Academy of Otolaryngology, the characterization of cancerous lymph nodes on CT scan, MRI or ultrasound is difficult, and usually requires confirmation by other nuclear imaging techniques such as PET scans. Tissue diagnosis by fine needle aspiration, may also be required, cervical lymph node metastasis is a common feature of papillary thyroid carcinoma Henri Rouvière produced an influential classification in 1938. More recently, classification systems have been proposed organized around what can be observed via diagnostic imaging, medEd at Loyola medicine/pulmonar/PD/pstep23. htm http, //www. patient. co. uk/showdoc/27000835/ anatomy of the cervical lymphatics
Cervical lymph nodes
–
Deep Lymph Nodes 1. Submental 2. Submandibular (Submaxillary) Anterior Cervical Lymph Nodes (Deep) 3. Prelaryngeal 4. Thyroid 5. Pretracheal 6. Paratracheal Deep Cervical Lymph Nodes 7. Lateral jugular 8. Anterior jugular 9. Jugulodigastric Inferior Deep Cervical Lymph Nodes 10. Juguloomohyoid 11. Supraclavicular (scalene)
Cervical lymph nodes
–
Regional lymph tissue. (Cervical near top, in green.)⋅
35.
Inguinal lymph nodes
–
Inguinal lymph nodes are a type of lymph node in the inguinal region. They can be superficial or deep, superomedial - located at the middle of the saphenous opening, take drainage from the perineum and outer genitalia. Deep inguinal lymph nodes arranged near and along the vein of the leg. Drain the deep parts of the limbs, womans clitoris. The mean size of a lymph node, as measured over the short-axis, is approximately 5.4 mm
Inguinal lymph nodes
–
Murine inguinal lymph node beneath the bifurcation of
epigastric vein. Bright structure visualised by
MHC II -
GFP construct, is the lymph node
36.
Tonsil
–
Tonsils are collections of lymphoid tissue facing into the aerodigestive tract. The set of tissue known as Waldeyers tonsillar ring includes the adenoid tonsil. When used unqualified, the term most commonly refers specifically to the palatine tonsils, the palatine tonsils and the nasopharyngeal tonsil are lymphoepithelial tissues located near the oropharynx and nasopharynx. Tonsils in humans include, from anterior, superior, posterior, and inferior, Tonsils tend to reach their largest size near puberty, however, they are largest relative to the diameter of the throat in young children. See also, The impact of tonsillectomy on the immune system These immunocompetent tissues are the systems first line of defense against ingested or inhaled foreign pathogens. Tonsils have on their surface specialized antigen capture cells called M cells that allow for the uptake of antigens produced by pathogens and these M cells then alert the underlying B cells and T cells in the tonsil that a pathogen is present and an immune response is stimulated. B cells are activated and proliferate in areas called germinal centres in the tonsil and these germinal centres are places where B memory cells are created and secretory antibody is produced. Recent studies have provided evidence that the tonsils produce T lymphocytes, also known as T-cells, in a similar to, but different from. Tonsils can become enlarged or inflamed and may require surgical removal and this may be indicated if they obstruct the airway or interfere with swallowing, or in patients with frequent recurrent tonsillitis. However, different mechanisms of pathogenesis for these two subtypes of tonsillar hypertrophy have been described, and may have different responses to identical therapeutic efforts, in older patients, asymmetric tonsils may be an indicator of virally infected tonsils, or tumors such as lymphoma or squamous cell carcinoma. Tonsillitis is a disorder in which the tonsils are inflamed, the most common way to treat it is with anti-inflammatory drugs such as ibuprofen, or if bacterial in origin, antibiotics, e. g. amoxicillin and azithromycin. Often severe and/or recurrent tonsillitis is treated by tonsillectomy, a tonsillolith is material that accumulates on the tonsil. They can range up to the size of a peppercorn and are white/cream in color, the main substance is mostly calcium, but they have a strong unpleasant odor because of hydrogen sulfide and methyl mercaptan and other chemicals. Tonsil enlargement can affect speech, making it hypernasal and giving it the sound of velopharyngeal incompetence, tonsil size may have a more significant impact on upper airway obstruction for obese children than for those of average weight. Other viewpoints treat them as large lymphatic organs contradistinguished from the smaller tissue loci of GALT and MALT, media related to Tonsils at Wikimedia Commons
Tonsil
–
Tonsil
Tonsil
–
A pair of tonsils after surgical removal.
37.
Paraaortic lymph nodes
–
The paraaortic lymph nodes are a group of lymph nodes that lie in front of the lumbar vertebrae near the aorta. These lymph nodes receive drainage from the tract and the abdominal organs. The paraaortic lymph node group is divided into three subgroups, preaortic, retroaortic, and right and left lateral aortic, the preaortic group drains the abdominal part of the gastrointestinal tract above the mid-rectum. The retroaortic group drains from the lateral and preaortic glands, the lateral aortic group drains the iliac lymph nodes, the ovaries, and other pelvic organs. The lateral group nodes are located adjacent to the aorta, anterior to the spine, extending laterally to the edge of the major muscles. The left lateral aortic glands form a chain on the side of the abdominal aorta in front of the origin of the psoas major. The lateral aortic lymph nodes, typically 15 to 20 on each side, are the ones usually chosen for dissection or biopsy in the treatment or diagnosis of cancer. A dissection usually includes the region from the bifurcation of the aorta to the superior mesenteric artery or the renal veins
Paraaortic lymph nodes
–
Left Lumbar Lymph Nodes (Paraaortic Lymph Nodes) 1. Lateral aortic 2. Preaortic 3. Postaortic 4. Intermediate Lumbar Right Lumbar Lymph Nodes (Paracaval Lymph Nodes) 5. Lateral caval 6. Precaval 7. Postcaval
Paraaortic lymph nodes
–
Lymph nodes (Paraaortic labeled in center in blue.)
38.
Blood-brain barrier
–
The blood–brain barrier is a highly selective semipermeable membrane barrier that separates the circulating blood from the brain extracellular fluid in the central nervous system. The blood–brain barrier is formed by brain cells, which are connected by tight junctions. Furthermore, it prevents the entry of lipophilic potential neurotoxins by way of a transport mechanism mediated by P-glycoprotein. Astrocytes have been claimed to be necessary to create the blood–brain barrier, a few regions in the brain, including the circumventricular organs, do not have a blood–brain barrier. The blood–brain barrier occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation, endothelial cells restrict the diffusion of microscopic objects and large or hydrophilic molecules into the cerebrospinal fluid, while allowing the diffusion of hydrophobic molecules. Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins and this barrier also includes a thick basement membrane and astrocytic endfeet. This barrier results from the selectivity of the junctions between endothelial cells in CNS vessels that restricts the passage of solutes. Each of these proteins is anchored into the endothelial cells by another protein complex that includes ZO-1. The blood–brain barrier is composed of high-density cells restricting passage of substances from the much more than do the endothelial cells in capillaries elsewhere in the body. Astrocyte cell projections called astrocytic feet surround the endothelial cells of the BBB, several areas of the human brain are not on the brain side of the BBB. Some examples of this include the organs, the roof of the third and fourth ventricles, capillaries in the pineal gland on the roof of the diencephalon. The pineal gland secretes the hormone melatonin directly into the systemic circulation, originally, experiments in the 1920s seemed to show that the blood–brain barrier was still immature in newborns. The reason for this mistake was an error in methodology and it was later shown in experiments with a reduced volume of the injected liquids that the markers under investigation could not pass the BBB. It was reported that those natural substances such as albumin, α-1-fetoprotein or transferrin with elevated plasma concentration in the newborn could not be detected outside of cells in the brain, the transporter P-glycoprotein exists already in the embryonal endothelium. Adult rabbits shows that newborn rabbit and adult rabbit brain endothelia are functionally similar with respect to lipid-mediated permeability and these data confirmed that no differences in permeability could be detected between newborn and adult BBB capillaries. No difference in brain uptake of glucose, amino acids, organic acids, purines, nucleosides and these experiments indicate that the newborn BBB has restrictive properties similar to that of the adult. In contrast to suggestions of a barrier in young animals. The blood–brain barrier acts very effectively to protect the brain from most pathogens, thus, blood-borne infections of the brain are very rare
Blood-brain barrier
–
Part of a network of
capillaries supplying
brain cells
Blood-brain barrier
–
The astrocytes type 1 surrounding capillaries in the brain
Blood-brain barrier
–
A cortical microvessel stained for blood–brain barrier protein ZO-1
Blood-brain barrier
–
Sketch showing constitution of blood vessels inside the brain
39.
T cells
–
A T cell, or T lymphocyte, is a type of lymphocyte that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells and they are called T cells because they mature in the thymus from thymocytes. The several subsets of T cells each have a distinct function, the majority of human T cells rearrange their alpha and beta chains on the cell receptor and are termed alpha beta T cells and are part of the adaptive immune system. The category of effector T cell is a one that includes various T cell types that actively respond to a stimulus. This includes helper, killer, regulatory, and potentially other T cell types, T helper cells assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages. These cells are known as CD4+ T cells because they express the CD4 glycoprotein on their surfaces. Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response. These cells can differentiate one of several subtypes, including TH1, TH2, TH3, TH17, TH9, or TFH. Signalling from the APC directs T cells into particular subtypes, cytotoxic T cells destroy virus-infected cells and tumor cells, and are also implicated in transplant rejection. These cells are known as CD8+ T cells since they express the CD8 glycoprotein at their surfaces. These cells recognize their targets by binding to antigen associated with MHC class I molecules, through IL-10, adenosine, and other molecules secreted by regulatory T cells, the CD8+ cells can be inactivated to an anergic state, which prevents autoimmune diseases. Appropriate co-stimulation must be present at the time of encounter for this process to occur. Historically, memory T cells were thought to belong to either the effector or central memory subtypes, subsequently, numerous new populations of memory T cells were discovered including tissue-resident memory T cells, stem memory TSCM cells, and virtual memory T cells. The single unifying theme for all memory T cell subtypes is that they are long-lived, by this mechanism they provide the immune system with memory against previously encountered pathogens. Memory T cells may be either CD4+ or CD8+ and usually express CD45RO, memory T cell subtypes, Central memory T cells express CD45RO, C-C chemokine receptor type 7, and L-selectin. Central memory T cells also have intermediate to high expression of CD44 and this memory subpopulation is commonly found in the lymph nodes and in the peripheral circulation. Effector memory T cells express CD45RO but lack expression of CCR7 and they also have intermediate to high expression of CD44. These memory T cells lack lymph node-homing receptors and are found in the peripheral circulation
T cells
–
Scanning electron micrograph of a human T cell
T cells
–
Scanning electron micrograph of T lymphocyte (right), a
platelet (center) and a
red blood cell (left)
40.
Antibody
–
An antibody, also known as an immunoglobulin, is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as bacteria and viruses. The antibody recognizes a molecule of the harmful agent, called an antigen. Each tip of the Y of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or a cell for attack by other parts of the immune system. Depending on the antigen, the binding may impede the process causing the disease or may activate macrophages to destroy the foreign substance. The ability of an antibody to communicate with the components of the immune system is mediated via its Fc region. The production of antibodies is the function of the humoral immune system. Antibodies are secreted by B cells of the immune system. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, soluble antibodies are released into the blood and tissue fluids, as well as many secretions to continue to survey for invading microorganisms. Antibodies are glycoproteins belonging to the immunoglobulin superfamily and they constitute most of the gamma globulin fraction of the blood proteins. They are typically made of basic structural units—each with two heavy chains and two small light chains. There are several different types of heavy chains that define the five different types of crystallisable fragments that may be attached to the antigen-binding fragments. The five different types of Fc regions allow antibodies to be grouped into five isotypes, each Fc region of a particular antibody isotype is able to bind to its specific Fc Receptor, thus allowing the antigen-antibody complex to mediate different roles depending on which FcR it binds. The ability of an antibody to bind to its corresponding FcR is further modulated by the structure of the present at conserved sites within its Fc region. The ability of antibodies to bind to FcRs helps to direct the immune response for each different type of foreign object they encounter. For example, IgE is responsible for an allergic response consisting of mast cell degranulation, igEs Fab paratope binds to allergic antigen, for example house dust mite particles, while its Fc region binds to Fc receptor ε. The allergen-IgE-FcRε interaction mediates allergic signal transduction to induce conditions such as asthma and this region is known as the hypervariable region. Each of these variants can bind to a different antigen and this enormous diversity of antibody paratopes on the antigen-binding fragments allows the immune system to recognize an equally wide variety of antigens
Antibody
–
Immunofluorescence image of the eukaryotic
cytoskeleton.
Actin filaments are shown in red,
microtubules in green, and the
nuclei in blue.
Antibody
–
Each antibody binds to a specific
antigen; an interaction similar to a lock and key.
Antibody
–
Example of tissue cross-reactivity on human
tissue microarray
Antibody
–
Angel of the West (2008) by
Julian Voss-Andreae is a sculpture based on the antibody structure published by E. Padlan. Created for the Florida campus of
the Scripps Research Institute, the antibody is placed into a ring referencing
Leonardo da Vinci's Vitruvian Man thus highlighting the similarity of the antibody and the human body.
41.
Memory T cell
–
Such T cells can recognize foreign invaders, such as bacteria or viruses, as well as cancer cells. Memory T cells have become experienced by having encountered antigen during an infection, encounter with cancer. At a second encounter with the invader, memory T cells can reproduce to mount a faster and stronger immune response than the first time the system responded to the invader. This behaviour is utilized in T lymphocyte proliferation assays, which can reveal exposure to specific antigens, within the overall memory T cell population, at least three distinct subpopulations have been described and can be recognised by the differential expression of chemokine receptor CCR7 and L-selectin. Central memory TCM cells express L-selectin and the CCR7, they secrete IL-2, effector memory TEM cells, however, do not express L-selectin or CCR7 but produce effector cytokines like IFNγ and IL-4. In mouse, this population would be highly expressive of CD44, more recently, other sub-populations have been explored using co-stimulatory molecules CD27 and CD28 expression in addition to CCR7 and CD62L. Those peripheral tissues are the skin, gut and joints, and are thought to be a key source of the immune systems protective memory, dysfunctional TRM cells are strongly implicated in autoimmune diseases, such as psoriasis, rheumatoid arthritis, inflammatory bowel disease. Specific to TRMs are genes involved in metabolism, being highly active. Antigen-specific memory T cells against viruses or other molecules can be found in both TCM and TEM subsets. Although most information is based on observations in the cytotoxic T cells subset. The TCM cells are thought to some properties associated with memory cells stem cells. TCM display a capacity for self-renewal due to levels of phosphorylation of an important transcription factor known as STAT5. In mice, TCM cells have shown to confer superior protection against viruses, bacteria. This population, now termed stem cell memory, can be identified by the markers CD44CD62LCD122sca-1 and are capable of generating TCM, in preclinical studies, adoptively transferred TSCM confer superior immunity compared with other T memory subsets. Whether such a population is found in humans is the subject of active investigation, naive T cell VJ recombination of DNA Memory B cell Janeway, Charles. Immunobiology, the system in health and disease. Lichtman, Andrew H. Abbas, Abul K
Memory T cell
–
A
lymphocyte is shown in the center of this picture
Memory T cell
42.
Apoptosis
–
Apoptosis is a process of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes and death and these changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay. Between 50 and 70 billion cells die each day due to apoptosis in the human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day, for example, the separation of fingers and toes in a developing human embryo occurs because cells between the digits undergo apoptosis. Because apoptosis cannot stop once it has begun, it is a regulated process. Apoptosis can be initiated through one of two pathways, in the intrinsic pathway the cell kills itself because it senses cell stress, while in the extrinsic pathway the cell kills itself because of signals from other cells. Both pathways induce cell death by activating caspases, which are proteases, the two pathways both activate initiator caspases, which then activate executioner caspases, which then kill the cell by degrading proteins indiscriminately. Research on apoptosis has increased substantially since the early 1990s, in addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in a wide variety of diseases. Excessive apoptosis causes atrophy, whereas an insufficient amount results in uncontrolled cell proliferation, some factors like Fas receptors and caspases promote apoptosis, while some members of the Bcl-2 family of proteins inhibit apoptosis. German scientist Karl Vogt was first to describe the principle of apoptosis in 1842, in 1885, anatomist Walther Flemming delivered a more precise description of the process of programmed cell death. However, it was not until 1965 that the topic was resurrected, while studying tissues using electron microscopy, John Foxton Ross Kerr at University of Queensland was able to distinguish apoptosis from traumatic cell death. Following the publication of a paper describing the phenomenon, Kerr was invited to join Alastair R Currie, as well as Andrew Wyllie, in 1972, the trio published a seminal article in the British Journal of Cancer. Kerr had initially used the term programmed cell necrosis, but in the article, Kerr, Wyllie and Currie credited James Cormack, a professor of Greek language at University of Aberdeen, with suggesting the term apoptosis. Kerr received the Paul Ehrlich and Ludwig Darmstaedter Prize on March 14,2000 and he shared the prize with Boston biologist H. Robert Horvitz. For many years, the apoptosis and programmed cell death were not highly cited. The 2002 Nobel Prize in Medicine was awarded to Sydney Brenner, Horvitz, the genes were identified by studies in the nematode C. elegans and homologues of these genes function in humans to regulate apoptosis. In Greek, apoptosis translates to the falling off of leaves from a tree, Cormack, professor of Greek language, reintroduced the term for medical use as it had a medical meaning for the Greeks over two thousand years before. Hippocrates used the term to mean the falling off of the bones, galen extended its meaning to the dropping of the scabs
Apoptosis
–
An
etoposide -treated
DU145 prostate cancer cell exploding into a cascade of apoptotic bodies. The sub images were extracted from a 61 hour
time-lapse microscopy video, created using
quantitative phase-contrast microscopy. The optical thickness is color-coded. With increasing thickness, color changes from gray to yellow, red, purple and finally black. See the video at The Cell: An Image Library
Apoptosis
–
John E. Sulston won the Nobel Prize in Medicine in 2002, for his pioneering research on apoptosis.
Apoptosis
–
Control Of The Apoptotic Mechanisms
Apoptosis
–
A section of mouse liver showing several apoptotic cells, indicated by arrows
43.
Antigens
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In immunology, an antigen is a molecule capable of inducing an immune response on the part of the host organism, though sometimes antigens can be part of the host itself. In other words, an antigen is any substance that causes a system to produce antibodies against it. In most cases, an antibody can bind one specific antigen, in some instances, however. An antigen is a molecule that binds to Ag-specific receptors, Antigens are usually peptides, polysaccharides or lipids. In general, molecules other than peptides qualify as antigens but not as immunogens since they cannot elicit a response on their own. Furthermore, for a peptide to induce a response it must be a large enough size. The term antigen originally described a structural molecule that specifically to an antibody. It expanded to refer to any molecule or a molecular fragment that can be recognized by highly variable antigen receptors of the adaptive immune system. The antigen may originate from within the body or from the external environment, antigen presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cells of the immune system recognize the antigens. Depending on the antigen and the type of the histocompatibility molecule, for T-Cell Receptor recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex. The antigen cannot elicit the immune response without the help of an immunologic adjuvant, similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system. An immunogen is a substance that is able to trigger a humoral and/or cell-mediated immune response and it first initiates an innate immune response, which then causes the activation of the adaptive immune response. An antigen binds the highly variable immunoreceptor products once these have been generated, all immunogen molecules are also antigens, although the reverse is not true. At the molecular level, an antigen can be characterized by its ability to bind to an antibodys variable Fab region, different antibodies have the potential to discriminate among specific epitopes present on the antigen surface. A hapten is a molecule that changes the structure of an antigenic epitope. In order to induce a response, it needs to be attached to a large carrier molecule such as a protein. Antigens are usually proteins and polysaccharides, and less frequently, lipids and this includes parts of bacteria, viruses, and other microorganisms
Antigens
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Contents
44.
Bacteria
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Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea
Bacteria
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Had'n
Bacteria
Bacteria
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A
biofilm of thermophilic bacteria in the outflow of
Mickey Hot Springs,
Oregon, approximately 20 mm thick.
Bacteria
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Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
45.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength
Cell wall
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Diagram of the plant cell, with the cell wall in green.
46.
Antigen-presenting cell
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An antigen-presenting cell or accessory cell is a cell that displays antigen complexed with major histocompatibility complexes on their surfaces, this process is known as antigen presentation. T cells may recognize these complexes using their T cell receptors and these cells process antigens and present them to T-cells. Almost all cell types can serve as form of APC. They are found in a variety of tissue types, in addition to the MHC family of proteins, antigen presentation relies on other specialized signaling molecules on the surfaces of both APCs and T cells. Antigen-presenting cells are vital for effective adaptive immune response, as the functioning of both cytotoxic and helper T cells is dependent on APCs, antigen presentation allows for specificity of adaptive immunity and can contribute to immune responses against both intracellular and extracellular pathogens. It is also involved in defense against tumors, some cancer therapies involve the creation of artificial APCs to prime the adaptive immune system to target malignant cells. Antigen-presenting cells fall into two categories, professional and non-professional and those that express MHC class II molecules along with co-stimulatory molecules and pattern recognition receptors are often called professional antigen-presenting cells. The non-professional APCs express MHC class I molecules, T cells must be activated by interacting with a professional APC presenting an antigen which their T cell receptor recognizes before they can divide and perform their function. The APC involved in activating T cells is usually a dendritic cell, T cells cannot recognize and therefore cannot respond to, free or soluble antigen. They can only recognize and respond to antigen that has processed and presented by cells via carrier molecules like MHC molecules. Helper T cells can recognize exogenous antigen presented on MHC class II, most cells in the body can present antigen to CD8+ cytotoxic T cells via MHC class I, however, the term antigen-presenting cell is often used specifically to describe professional APCs. Such cells express MHC class I and MHC class II molecules, APCs can also present foreign and self lipids to T cells and NK cells by using the CD1 family of proteins, which are structurally similar to the MHC class I family. Professional APCs specialize in presenting antigen to T cells, the T cell recognizes and interacts with the antigen-class II MHC molecule complex on the membrane of the antigen-presenting cell. An additional co-stimulatory signal is produced by the antigen-presenting cell. The expression of molecules and MHC class II are defining features of professional APCs. All professional APCs also express MHC class I molecules as well, the main types of professional antigen-presenting cells are dendritic cells, macrophages and B cells. Dendritic cells have the broadest range of antigen presentation and are necessary for activation of naive T cells, dCs present antigen to both helper and cytotoxic T cells. They can also perform cross-presentation, a process by which they present exogenous antigen on MHC class I molecules to cytotoxic T cells, cross-presentation allows for the activation of these T cells
Antigen-presenting cell
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Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.
47.
Dendritic cells
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Dendritic cells are antigen-presenting cells of the mammalian immune system. Their main function is to process antigen material and present it on the surface to the T cells of the immune system. They act as messengers between the innate and the immune systems. Dendritic cells are present in tissues that are in contact with the external environment, such as the skin. They can also be found in a state in the blood. Once activated, they migrate to the nodes where they interact with T cells and B cells to initiate. At certain development stages they grow branched projections, the dendrites that give the cell its name, while similar in appearance, these are structures distinct from the dendrites of neurons. Immature dendritic cells are also called veiled cells, as they possess large cytoplasmic veils rather than dendrites, dendritic cells were first described by Paul Langerhans in the late nineteenth century. The term dendritic cells was coined in 1973 by Ralph M. Steinman, the morphology of dendritic cells results in a very large surface-to-volume ratio. That is, the cell has a very large surface area compared to the overall cell volume. The most common division of cells is myeloid vs. plasmacytoid, The markers BDCA-2, BDCA-3. Lymphoid and myeloid DCs evolve from lymphoid and myeloid precursors, respectively, the blood DCs are typically identified and enumerated in flow cytometry. Three types of DCs have been defined in human blood, the CD1c+ myeloid DCs, the CD141+ myeloid DCs and this represents the nomenclature proposed by the nomenclature committee of the International Union of Immunological Societies. Dendritic cells that circulate in blood do not have all the features of their counterparts in tissue. Still, they can perform functions including chemokine-production, cross-presentation. In some respects, dendritic cells cultured in vitro do not show the behaviour or capability as dendritic cells isolated ex vivo. Nonetheless, they are used for research as they are still much more readily available than genuine DCs. Mo-DC or MDDC refers to cells matured from monocytes HP-DC refers to cells derived from hematopoietic progenitor cells, while humans and non-human primates such as rhesus macaques appear to have DCs divided into these groups, other species have different subdivisions of DCs
Dendritic cells
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Dendritic cells in skin
Dendritic cells
Dendritic cells
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A dendritic cell
48.
Lymphatic vessels
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In anatomy, lymphatic vessels are thin-walled, valved structures that carry lymph. As part of the system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and have a layer of smooth muscles. Lymph vessels are devoted to propulsion of the lymph from the lymph capillaries, lymph capillaries are slightly larger than their counterpart capillaries of the vascular system. Lymph ducts drain the lymph into one of the subclavian veins, generally, lymph flows away from the tissues to lymph nodes and eventually to either the right lymphatic duct or the largest lymph vessel in the body, the thoracic duct. These vessels drain into the right and left subclavian veins respectively, the general structure of lymphatics is based on that of blood vessels. There is a lining of single flattened epithelial cells composed of a type of epithelium that is called endothelium. This layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous, the next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening or relaxing alter the diameter of the lumen. The outermost layer is the adventitia that consists of fibrous tissue, the general structure described here is seen only in larger lymphatics, smaller lymphatics have fewer layers. The smallest vessels lack both the muscular layer and the outer adventitia, as they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, and then smooth muscles. Unlike the cardiovascular system, the system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis, valves and these button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF, there is another system of semilunar valves that prevents back-flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections between them and form a fine network. Rhythmic contraction of the walls through movements may also help draw fluid into the smallest lymphatic vessels. If tissue fluid builds up the tissue will swell, this is called edema, the system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a circulatory system. The lymph capillaries drain the lymph to larger contractile lymphatics, which have valves as well as smooth muscle walls and these are called the collecting lymphatics
Lymphatic vessels
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Lymph capillaries in the tissue spaces.
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