1.
Optical microscope
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The optical microscope, often referred to as light microscope, is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were invented in their present compound form in the 17th century. Basic optical microscopes can be simple, although there are many complex designs which aim to improve resolution. The image from a microscope can be captured by normal light-sensitive cameras to generate a micrograph. Originally images were captured by photographic film but modern developments in CMOS, purely digital microscopes are now available which use a CCD camera to examine a sample, showing the resulting image directly on a computer screen without the need for eyepieces. Alternatives to optical microscopy which do not use visible light include scanning electron microscopy, there are two basic types of optical microscopes, simple microscopes and compound microscopes. A simple microscope is one which uses a lens for magnification. A compound microscope uses several lenses to enhance the magnification of an object, the vast majority of modern research microscopes are compound microscopes while some cheaper commercial digital microscopes are simple single lens microscopes. Compound microscopes can be divided into a variety of other types of microscopes which differ in their optical configurations, cost. A simple microscope uses a lens or set of lenses to enlarge an object through angular magnification alone, the use of a single convex lens or groups of lenses are still found in simple magnification devices such as the magnifying glass, loupes, and eyepieces for telescopes and microscopes. A compound microscope uses a close to the object being viewed to collect light which focuses a real image of the object inside the microscope. That image is magnified by a second lens or group of lenses that gives the viewer an enlarged inverted virtual image of the object. The use of a compound objective/eyepiece combination allows for higher magnification. Common compound microscopes often feature exchangeable objective lenses, allowing the user to quickly adjust the magnification, a compound microscope also enables more advanced illumination setups, such as phase contrast. There are many variants of the optical microscope design for specialized purposes. Comparison microscope, which has two light paths allowing direct comparison of two samples via one image in each eye. Inverted microscope, for studying samples from below, useful for cell cultures in liquid, student microscope, designed for low cost, durability, and ease of use. Polarizing microscope, similar to the petrographic microscope, phase contrast microscope, which applies the phase contrast illumination method
2.
Red blood cell
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RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the bodys capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, a biomolecule that can bind oxygen and is responsible for the red color of the cells. In humans, mature red cells are flexible and oval biconcave disks. They lack a nucleus and most organelles, in order to accommodate maximum space for hemoglobin, they can be viewed as sacks of hemoglobin. Approximately 2.4 million new erythrocytes are produced per second in human adults, the cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds, approximately a quarter of the cells in the human body are red blood cells. Nearly half of the volume is red blood cells. Red blood cells are known as RBCs, red cells, red blood corpuscles, haematids. Packed red blood cells are red blood cells that have donated, processed. Almost all vertebrates, including all mammals and humans, have red blood cells, red blood cells are cells present in blood in order to transport oxygen. The only known vertebrates without red blood cells are the crocodile icefish, they live in very cold water. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome, oxygen can easily diffuse through the red blood cells cell membrane. Myoglobin, a related to hemoglobin, acts to store oxygen in muscle cells. The color of red cells is due to the heme group of hemoglobin. However, blood can appear bluish when seen through the vessel wall, pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin also has a high affinity for carbon monoxide, forming carboxyhemoglobin which is a very bright red in color. Flushed, confused patients with a reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. The red blood cells of mammals are typically shaped as disks, flattened and depressed in the center, with a dumbbell-shaped cross section
3.
White blood cell
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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
4.
Human
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Modern humans are the only extant members of Hominina tribe, a branch of the tribe Hominini belonging to the family of great apes. Several of these hominins used fire, occupied much of Eurasia and they began to exhibit evidence of behavioral modernity around 50,000 years ago. In several waves of migration, anatomically modern humans ventured out of Africa, the spread of humans and their large and increasing population has had a profound impact on large areas of the environment and millions of native species worldwide. Humans are uniquely adept at utilizing systems of communication for self-expression and the exchange of ideas. Humans create complex structures composed of many cooperating and competing groups, from families. Social interactions between humans have established a wide variety of values, social norms, and rituals. These human societies subsequently expanded in size, establishing various forms of government, religion, today the global human population is estimated by the United Nations to be near 7.5 billion. In common usage, the word generally refers to the only extant species of the genus Homo—anatomically and behaviorally modern Homo sapiens. In scientific terms, the meanings of hominid and hominin have changed during the recent decades with advances in the discovery, there is also a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species. The English adjective human is a Middle English loanword from Old French humain, ultimately from Latin hūmānus, the words use as a noun dates to the 16th century. The native English term man can refer to the species generally, the species binomial Homo sapiens was coined by Carl Linnaeus in his 18th century work Systema Naturae. The generic name Homo is a learned 18th century derivation from Latin homō man, the species-name sapiens means wise or sapient. Note that the Latin word homo refers to humans of either gender, the genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids branch of the primates. The closest living relatives of humans are chimpanzees and gorillas, with the sequencing of both the human and chimpanzee genome, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%. The gibbons and orangutans were the first groups to split from the leading to the humans. The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch, during this split, chromosome 2 was formed from two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. There is little evidence for the divergence of the gorilla, chimpanzee. Each of these species has been argued to be an ancestor of later hominins
5.
Amoeba
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An amoeba, often called amoeboid, is a type of cell or organism which has the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebas do not form a taxonomic group, instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, microbiologists often use the terms amoeboid and amoeba interchangeably for any organism that exhibits amoeboid movement. In older classification systems, most amoebas were placed in the class or subphylum Sarcodina, however, molecular phylogenetic studies have shown that Sarcodina is not a monophyletic group whose members share common descent. Consequently, amoeboid organisms are no longer classified together in one group, the best known amoeboid protists are the Giant Amoebae Chaos carolinense and Amoeba proteus, both of which are widely cultivated and studied in classrooms and laboratories. Amoebae move and feed by using pseudopods, which are bulges of cytoplasm formed by the action of actin microfilaments pushing out the plasma membrane that surrounds the cell. The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another, amoebozoan species, such as those in the genus Amoeba, typically have bulbous pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as Euglypha and Gromia, have slender, foraminifera emit fine, branching pseudopods that merge with one another to form net-like structures. Some groups, such as the Radiolaria and Heliozoa, have stiff, needle-like, free-living amoebae may be testate, or naked. The shells of testate amoebae may be composed of substances, including calcium, silica, chitin, or agglutinations of found materials like small grains of sand. To regulate osmotic pressure, most freshwater amoebae have a contractile vacuole which expels excess water from the cell and this organelle is necessary because freshwater has a lower concentration of solutes than the amoebas own internal fluids. Because the surrounding water is hypotonic with respect to the contents of the cell, without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole, because the concentration of solutes within the cell are in balance with the tonicity of the surrounding water, the food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other protists, Some are detritivores and eat dead organic material. Amoebae typically ingest their food by phagocytosis, extending pseudopods to encircle, Amoeboid cells do not have a mouth or cytostome, and there is no fixed place on the cell at which phagocytosis normally occurs. Some amoebae also feed by pinocytosis, imbibing dissolved nutrients through vesicles formed within the cell membrane, the size of amoeboid cells and species is extremely variable. The marine amoeboid Massisteria voersi is just 2.3 to 3 micrometres in diameter, at the other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter. Some multicellular organisms have amoeboid cells only in certain phases of life, in the immune system of humans and other animals, amoeboid white blood cells pursue invading organisms, such as bacteria and pathogenic protists, and engulf them by phagocytosis
6.
Inflammation
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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
7.
Antibody
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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
8.
Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
9.
Blood
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Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells suspended in blood plasma, plasma, which constitutes 55% of blood fluid, is mostly water, and contains dissipated proteins, glucose, mineral ions, hormones, carbon dioxide, and blood cells themselves. Albumin is the protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are red blood cells, white blood cells. The most abundant cells in blood are red blood cells. These contain hemoglobin, a protein, which facilitates oxygen transport by reversibly binding to this respiratory gas. In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma, vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this blood does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their system to suffice for supplying oxygen. Jawed vertebrates have an immune system, based largely on white blood cells. White blood cells help to resist infections and parasites, platelets are important in the clotting of blood. Arthropods, using hemolymph, have hemocytes as part of their immune system, Blood is circulated around the body through blood vessels by the pumping action of the heart. Medical terms related to blood often begin with hemo- or hemato- from the Greek word αἷμα for blood. In terms of anatomy and histology, blood is considered a form of connective tissue, given its origin in the bones. The average adult has a volume of roughly 5 litres. These blood cells consist of erythrocytes, leukocytes, and thrombocytes, by volume, the red blood cells constitute about 45% of whole blood, the plasma about 54. 3%, and white cells about 0. 7%. Whole blood exhibits non-Newtonian fluid dynamics, if all human hemoglobin were free in the plasma rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function effectively. One microliter of blood contains,4.7 to 6.1 million,4.2 to 5.4 million erythrocytes, Red blood cells contain the bloods hemoglobin, mature red blood cells lack a nucleus and organelles in mammals
10.
Granulocyte
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Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the shapes of the nucleus. This distinguishes them from the mononuclear agranulocytes, in common parlance, the term polymorphonuclear leukocyte often refers specifically to neutrophil granulocytes, the most abundant of the granulocytes, the other types have lower numbers. Granulocytes are produced via granulopoiesis in the bone marrow, neutrophils are normally found in the bloodstream and are the most abundant type of phagocyte, constituting 50% to 60% of the total circulating white blood cells. One litre of blood contains about five billion neutrophils, which are about 12–15 micrometers in diameter. Once neutrophils have received the signals, it takes them about thirty minutes to leave the blood. Neutrophils do not return to the blood, they turn into pus cells, mature neutrophils are smaller than monocytes, and have a segmented nucleus with several sections, each section is connected by chromatin filaments. Neutrophils do not normally exit the bone marrow until maturity, neutrophils have three strategies for directly attacking micro-organisms, phagocytosis, release of soluble anti-microbials, and generation of neutrophil extracellular traps. Neutrophils are professional phagocytes, they are ferocious eaters and rapidly engulf invaders coated with antibodies and complement, the intracellular granules of the human neutrophil have long been recognized for their protein-destroying and bactericidal properties. Neutrophils can secrete products that stimulate monocytes and macrophages, these secretions increase phagocytosis, neutrophils have two types of granules, primary granules and secondary granules. In addition, secretions from the granules of neutrophils stimulate the phagocytosis of IgG antibody-coated bacteria. The secondary granules contain compounds that are involved in the formation of oxygen compounds, lysozyme. Neutrophil extracellular traps comprise a web of fibers composed of chromatin and serine proteases that trap, trapping of bacteria is a particularly important role for NETs in sepsis, where NET are formed within blood vessels. Eosinophils also have kidney-shaped lobed nuclei, the number of granules in an eosinophil can vary because they have a tendency to degranulate while in the blood stream. A polypeptide called interleukin-5 interacts with eosinophils and causes them to grow and differentiate, basophils are one of the least abundant cells in bone marrow and blood. Like neutrophils and eosinophils, they have lobed nuclei, however, basophils have receptors that can bind to IgE, IgG, complement, and histamine. The cytoplasm of basophils contains an amount of granules, these granules are usually numerous enough to partially conceal the nucleus. Granule contents of basophils are abundant with histamine, heparin, chondroitin sulfate, peroxidase, platelet-activating factor, when an infection occurs, mature basophils will be released from the bone marrow and travel to the site of infection
11.
Dendritic cell
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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
12.
Cellular differentiation
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In developmental biology, cellular differentiation is the process where a cell changes from one cell type to another. Most commonly the cell changes to a specialized type. Differentiation occurs numerous times during the development of an organism as it changes from a simple zygote to a complex system of tissues. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair, some differentiation occurs in response to antigen exposure. Differentiation dramatically changes a cells size, shape, membrane potential, metabolic activity and these changes are largely due to highly controlled modifications in gene expression and are the study of epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself, thus, different cells can have very different physical characteristics despite having the same genome. There are multiple levels of potency, the cells ability to differentiate into other cell types. A greater potency indicates a number of cells that can be derived. A cell that can differentiate into all types, including the placental tissue, is known as totipotent. In mammals, only the zygote and subsequent blastomeres are totipotent, a cell that can differentiate into all cell types of the adult organism is known as pluripotent. Such cells are called meristematic cells in plants and embryonic stem cells in animals. Virally induced expression of four transcription factors Oct4, Sox2, c-Myc, a multipotent cell is one that can differentiate into multiple different, but closely related cell types. Oligopotent cells are more restricted than multipotent, but can still differentiate into a few closely related cell types, finally, unipotent cells can differentiate into only one cell type, but are capable of self-renewal. In cytopathology, the level of differentiation is used as a measure of cancer progression. Grade is a marker of how differentiated a cell in a tumor is, three basic categories of cells make up the mammalian body, germ cells, somatic cells, and stem cells. Most cells are diploid, they have two copies of each chromosome, such cells, called somatic cells, make up most of the human body, such as skin and muscle cells. Cells differentiate to specialize for different functions, germ line cells are any line of cells that give rise to gametes—eggs and sperm—and thus are continuous through the generations. Stem cells, on the hand, have the ability to divide for indefinite periods
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