Lymph node
A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system, of the adaptive immune system, present throughout the body. They are linked by the lymphatic vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, other white blood cells. 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 detoxification function, dealt with by the liver and kidneys. 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 have clinical significance, they become inflamed or enlarged in various diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the lymph nodes is important in cancer staging, which decides the treatment to be used, determines the prognosis; when swollen, inflamed or enlarged, lymph nodes can be hard, tender.
Lymph nodes are oval shaped and range in size from a few millimeters to about 1 -- 2 cm long. Each lymph node is surrounded by a fibrous capsule, which extends inside the lymph node to form trabeculae; the substance of the lymph node is divided into the inner medulla. The cortex is continuous around the medulla except where the medulla comes into direct contact with the hilum. Thin reticular fibers of reticular connective tissue, elastin form a supporting meshwork called a reticulin inside the node. B cells are found in the outer cortex where they are clustered together as follicular B cells in lymphoid follicles and the T cells are in the paracortex; the lymph node is divided into compartments called lymph nodules each consisting of a cortical region of combined follicle B cells, a paracortical region of T cells, a basal part of the nodule in the medulla. The number and composition of follicles can change when challenged by an antigen, when they develop a germinal center. Elsewhere in the node, there are only occasional leukocytes.
As part of the reticular network there are follicular dendritic cells in the B cell follicle and fibroblastic reticular cells in the T cell cortex. The reticular network not only provides the structural support, but the surface for adhesion of the dendritic cells and lymphocytes, 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. Lymph enters the convex side of the lymph node through multiple afferent lymphatic vessels, flows through spaces called sinuses. A lymph sinus which includes the subcapsular sinus, is a channel within the node, lined by endothelial cells along with fibroblastic reticular cells and this allows for the smooth flow of lymph through them; the endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and with that of the similar sinuses flanking the trabeculae and within the cortex. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses, from where the lymph flows into the efferent lymph vessels to exit the node at the hilum on the concave side.
These vessels are smaller and don't 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 adaptive immune response; the lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, from its internal surface are given off a number of membranous processes or trabeculae. They pass inward, radiating toward the center of the node, for about one-third or one-fourth of the space between the circumference and the center of the node. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments, but in humans this arrangement is not obvious; the larger trabeculae springing from the capsule break up into finer bands, these interlace to form a mesh-work in the central or medullary portion of the node. In these trabecular spaces formed by the interlacing trabeculae is contained the proper lymph node substance or lymphoid tissue.
The node pulp does not, however fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout. This is termed the subcapsular sinus. Running across it are a number of finer trabeculae of reticular connective tissue, the fibers of which are, for the most part, covered by ramifying cells; the subcapsular sinus is the space between the capsule and the cortex which allows the free movement of lymphatic fluid and so contains few lymphocytes. It is continuous with the similar lymph sinuses; the lymph node contains lymphoid tissue, i.e. a meshwork or fibers called reticulum with white blood cells enmeshed in it. The regions where there are few cells within the meshwork are known as lymph sinus, it is lined by reticular cells and fixed macrophages. The subcapsular sinus has clinical importance as it is the most location where the earliest manifestations of a metastatic carcinoma in a lymph node would be found; the cortex of the lymph node is the outer portion of the node, underneath the capsule and the subcapsular sinus.
It has a deeper part known as the paracortex. The subcapsular sinus drains to the trabecul sinuses, the lymph flows into the medullary sinuses; the outer cortex consists of the B c
Pulmonary pleurae
The pulmonary pleurae are the two pleurae of the invaginated sac surrounding each lung and attaching to the thoracic cavity. The visceral pleura is the delicate serous membrane that covers the surface of each lung and dips into the fissures between the lobes; the parietal pleura is the outer membrane, attached to the inner surface of the thoracic cavity. It separates the pleural cavity from the mediastinum; the parietal pleura is innervated by the phrenic nerve. Between the membranes is a fluid-filled space called the pleural cavity; the visceral pleura is a delicate serous membrane that covers the surfaces of the lungs and dips into the fissures that separate the lobes. The parietal pleura is the outer membrane that attaches to and lines the inner surface of the thoracic cavity, covers the upper surface of the diaphragm and is reflected over structures within the middle of the thorax, it separates the pleural cavity from the mediastinum. The parietal pleura is differentiated into regions in line with the location in the thorax.
The "cervical pleura" is in the region of the cervical vertebrae extending beyond the apex of the lung and into the neck. The "costal pleura" lines the inner surfaces of the ribs and the intercostal muscles and are separated from them by endothoracic fascia. An extension of the endothoracic fascia known as the suprapleural membrane covers the apex of each lung in a thickened layer of connective tissue; the "diaphragmatic pleura" lines the convex surface of the diaphragm. The "mediastinal pleura" attaches to the other organs in the mediastinum and forms the separating lateral wall. Between the two membranes is a space called the pleural cavity or interpleural space, which contains a lubricating fluid; as it reaches the 4th rib – atria 8th rib – mid clavicular 10th rib – axillary area 12th rib – back side The parietal pleura is supplied by the intercostal nerves and the phrenic nerve. The costal pleura is innervated by the intercostal nerves; the diaphragmatic portion of the parietal pleura overlies the diaphragm and is innervated by the phrenic nerve in its central portion and by the intercostal nerves in its peripheral portion.
The mediastinal portion of the parietal pleura forms the lateral wall of the mediastinum and is innervated by the phrenic nerve. The visceral and parietal pleurae both derive from the lateral plate mesoderm which splits into two layers the somatopleuric mesoderm forming the parietal membrane and the splanchnopleuric mesoderm of the visceral membrane; the contraction of the diaphragm creates a negative pressure within the pleural cavity which forces the lungs to expand resulting in passive exhalation and active inhalation. This breathing process can be made forceful through the contraction of the external intercostal muscles which forces the rib cage to expand and add to the negative pressure in the pleural cavity causing the lungs to fill with air; the fluid in the cavity provides cushioning. Pleurisy is a condition of inflamed pleurae. Pleurisy can lead to a build-up of fluid known as pleural effusion in the pleural cavity. Pleural effusion can occur from other causes. Light, Richard W.. Pleural Diseases.
Lippincott Williams & Wilkins. ISBN 978-0781769570. Thoraxlesson2 at The Anatomy Lesson by Wesley Norman Atlas image: lung_pleura at the University of Michigan Health System - "X-ray, posteroanterior view" Atlas image: lung_lymph at the University of Michigan Health System - "Transverse section through lung" MedEd at Loyola Grossanatomy/thorax0/thor_lec/thor6.html Diagram at kent.edu
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell, a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes. Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor. Prokaryotes undergo a vegetative cell division known as binary fission, where their genetic material is segregated into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.
For simple unicellular microorganisms such as the amoeba, one cell division is equivalent to reproduction – an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by meiotic cell division from gametes. After growth, cell division by mitosis allows for continual repair of the organism; the human body experiences about 10 quadrillion cell divisions in a lifetime. The primary concern of cell division is the maintenance of the original cell's genome. Before division can occur, the genomic information, stored in chromosomes must be replicated, the duplicated genome must be separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between generations. Interphase is the process a cell must go through before mitosis and cytokinesis.
Interphase consists of three main stages: G1, S, G2. G1 is a time of growth for the cell where specialized cellular functions occur in order to prepare the cell for DNA Replication. There are checkpoints during interphase that allow the cell to be either progressed or denied further development. In S phase, the chromosomes are replicated in order for the genetic content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase, where spindles are synthesized; the M phase, can be either meiosis depending on the type of cell. Germ cells, or gametes, undergo meiosis. After the cell proceeds through the M phase, it may undergo cell division through cytokinesis; the control of each checkpoint is controlled by cyclin and cyclin dependent kinases. The progression of interphase is the result of the increased amount of cyclin; as the amount of cyclin increases and more cyclin dependent kinases attach to cyclin signaling the cell further into interphase. The peak of the cyclin attached to the cyclin dependent kinases this system pushes the cell out of interphase and into the M phase, where mitosis and cytokinesis occur.
There are three transition checkpoints. The most important being the G1-S transition checkpoint. If the cell does not pass this phase the cell will most not go through the rest of the cell division cycle. Prophase is the first stage of division; the nuclear envelope is broken down, long strands of chromatin condense to form shorter more visible strands called chromosomes, the nucleolus disappears, microtubules attach to the chromosomes at the kinetochores present in the centromere. Microtubules associated with the alignment and separation of chromosomes are referred to as the spindle and spindle fibers. Chromosomes will be visible under a microscope and will be connected at the centromere. During this condensation and alignment period, homologous over. In metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate, an imaginary line, equidistant from the two centrosome poles. Chromosomes line up in the middle of the cell by MTOCs by pushing and pulling on centromeres of both chromatids which causes the chromosome to move to the center.
The chromosomes are still condensing and are at one step away from being the most coiled and condensed they will be. Spindle fibres have connected to the kinetochores. At this point, the chromosomes are ready to split into opposite poles of the cell towards the spindle to which they are connected. Anaphase is a short stage of the cell cycle and occurs after the chromosomes align at the mitotic plate. After the chromosomes line up in the middle of the cell, the spindle fibers will pull them apart; the chromosomes are split apart as the sister chromatids move to opposite sides of the cell. While the sister chromatids are being pulled apart and plasma gets elongated from non-kinetochore microtubules Telophase is the last stage of the cell cycle. A cleavage furrow splits the cell in two; these two cells form around the chromatin at the two poles of the cell. Two nuclear membranes begin to reform and the chromatin begin to unwind. Cells are broadly classified into two main categories: simple, non-nucleated prokaryotic cells, complex, nucleated eukaryotic cells.
Owing to their structural differences and prokaryotic cells do not divide in the same way. The pattern of cell division that tr
Microscope slide
A microscope slide is a thin flat piece of glass 75 by 26 mm and about 1 mm thick, used to hold objects for examination under a microscope. The object is mounted on the slide, both are inserted together in the microscope for viewing; this arrangement allows several slide-mounted objects to be inserted and removed from the microscope, labeled and stored in appropriate slide cases or folders etc. Microscope slides are used together with a cover slip or cover glass, a smaller and thinner sheet of glass, placed over the specimen. Slides are held in place on the microscope's stage by slide clips, slide clamps or a cross-table, used to achieve precise, remote movement of the slide upon the microscope's stage The origin of the concept was pieces of ivory or bone, containing specimens held between disks of transparent mica, that would slide into the gap between the stage and the objective; these "sliders" were popular in Victorian England until the Royal Microscopical Society introduced the standardized glass microscope slide.
A standard microscope slide is about 1 mm thick. A range of other sizes are available for various special purposes, such as 75 x 50 mm for geological use, 46 x 27 mm for petrographic studies, 48 x 28 mm for thin sections. Slides are made of common glass and their edges are finely ground or polished. Microscope slides are made of optical quality glass, such as soda lime glass or borosilicate glass, but specialty plastics are used. Fused quartz slides are used when ultraviolet transparency is important, e.g. in fluorescence microscopy. While plain slides are the most common, there are several specialized types. A concavity slide or cavity slide has one or more shallow depressions, designed to hold thicker objects, certain samples such as liquids and tissue cultures. Slides may have rounded corners for increased safety or robustness, or a cut-off corner for use with a slide clamp or cross-table, where the slide is secured by a spring-loaded curved arm contacting one corner, forcing the opposing corner of the slide against a right angled arm which does not move.
If this system were used with a slide which did not incorporate these cut-off corners, the corners would chip and the slide could shatter. A graticule slide is marked with a grid of lines that allows the size of objects seen under magnification to be estimated and provides reference areas for counting minute objects. Sometimes one square of the grid will itself be subdivided into a finer grid. Slides for specialized applications, such as hemocytometers for cell counting, may have various reservoirs and barriers etched or ground on their upper surface. Various permanent markings or masks may be printed, sand-blasted, or deposited on the surface by the manufacturer with inert materials such as PTFE; some slides have a frosted or enamel-coated area for labeling with a pencil or pen. Slides may have special coatings applied by the manufacturer, e.g. for chemical inertness or enhanced cell adhesion. The coating may have a permanent electric charge to hold powdery samples. Common coatings include poly-L-lysine, epoxy resins, or gold.
The mounting of specimens on microscope slides is critical for successful viewing. The problem has been given much attention in the last two centuries and is a well-developed area with many specialized and sometimes quite sophisticated techniques. Specimens are held into place using the smaller glass cover slips; the main function of the cover slip is to keep solid specimens pressed flat, liquid samples shaped into a flat layer of thickness. This is necessary because high-resolution microscopes have a narrow region within which they focus; the cover glass has several other functions. It protects the specimen from dust and accidental contact, it protects the microscope's objective lens from contacting the vice versa. The cover slip can be glued to the slide so as to seal off the specimen, retarding dehydration and oxidation of the specimen and preventing contamination. A number of sealants are in use, including commercial sealants, laboratory preparations, or regular clear nail polish, depending on the sample.
A solvent-free sealant that can be used for live cell samples is "valap", a mixture of vaseline and paraffin in equal parts. Microbial and cell cultures can be grown directly on the cover slip before it is placed on the slide, specimens may be permanently mounted on the slip instead of on the slide. Cover slips are available in a range of thicknesses. Using the wrong thickness can result in spherical aberration and a reduction in resolution and image intensity. Specialty objectives may used to image specimens without coverslips, or may have correction collars that permit a user to accommodate for alternative coverslip thickness. In a dry mount, the simplest kind of mounting, the object is placed on the slide. A cover slip may be placed on top to protect the specimen and the microscope's objective and to keep the specimen still and pressed flat; this mounting can be used for viewing specimens like pollen, hairs, etc. It is used to examine particles caught i
Organ (anatomy)
Organs are groups of tissues with similar functions. Plant and animal life relies on many organs. Organs are composed of main tissue, "sporadic" tissues, stroma; the main tissue is that, unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, connective tissues. The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer. Functionally-related organs cooperate to form whole organ systems. Organs exist in most multicellular organisms. In single-celled organisms such as bacteria, the functional analogue of an organ is known as an organelle. In plants there are three main organs. A hollow organ is an internal organ that forms a hollow tube, or pouch such as the stomach, intestine, or bladder. In the study of anatomy, the term viscus is used to refer to an internal organ, viscera is the plural form. 79 organs have been identified in the human body. In biology, tissue is a cellular organizational level between complete organs.
A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant morphology. Classical tools for studying tissues include the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis. Two or more organs working together in the execution of a specific body function form an organ system called a biological system or body system.
The functions of organ systems share significant overlap. For instance, the nervous and endocrine system both operate via the hypothalamus. For this reason, the two systems are studied as the neuroendocrine system; the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Common organ system designations in plants includes the differentiation of root. All parts of the plant above ground, including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system. Animals such as humans have a variety of organ systems; these specific systems are widely studied in human anatomy. Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart and blood vessels. Digestive system: digestion and processing food with salivary glands, stomach, gallbladder, intestines, colon and anus. Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid and adrenals, i.e. adrenal glands.
Excretory system: kidneys, ureters and urethra involved in fluid balance, electrolyte balance and excretion of urine. Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, adenoids and spleen. Integumentary system: skin and nails of mammals. Scales of fish and birds, feathers of birds. Muscular system: movement with muscles. Nervous system: collecting and processing information with brain, spinal cord and nerves. Reproductive system: the sex organs, such as ovaries, fallopian tubes, vulva, testes, vas deferens, seminal vesicles and penis. Respiratory system: the organs used for breathing, the pharynx, trachea, bronchi and diaphragm. Skeletal system: structural support and protection with bones, cartilage and tendons; 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 reproductive. Vegetative plant organs include roots and leaves; the reproductive organs are variable. In flowering plants, they are represented by the flower and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions of plants, the reproductive organs are called strobili, in Lycopodiophyta, or gametophores in mosses; the vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis, while the reproductive organs are essential in reproduction. However, if there is asexual vegetative reproduction, the vegetative organs are those that create the new generation of plants. Many societies have a system for organ donation, in which a living or deceased donor's organ is transplanted into a person with a failing organ; the transplantation of larger solid organs requires immunosuppression to prevent organ rejection or graft-versus-host disease.
There is considerable interest throughout the world in creating laboratory-grown or artificial organs. The English word "organ" dates back in reference to any musical instrument. By the late 14th
Micrograph
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image, taken on a microscope but is only magnified less than 10 times. Micrography is the art of using microscopes to make photographs. A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are used in all fields of microscopy. A light micrograph or photomicrograph is a micrograph prepared using an optical microscope, a process referred to as photomicroscopy. At a basic level, photomicroscopy may be performed by connecting a camera to a microscope, thereby enabling the user to take photographs at reasonably high magnification. Scientific use began in England in 1850 by Prof Richard Hill Norris FRSE for his studies of blood cells.
Roman Vishniac was a pioneer in the field of photomicroscopy, specializing in the photography of living creatures in full motion. He made major developments in light-interruption photography and color photomicroscopy. Photomicrographs may be obtained using a USB microscope attached directly to a home computer or laptop. An electron micrograph is a micrograph prepared using an electron microscope. Micrographs have micron bars, or magnification ratios, or both. Magnification is a ratio between the size of an object on its real size. Magnification can be a misleading parameter as it depends on the final size of a printed picture and therefore varies with picture size. A scale bar, or micron bar, is a line of known length displayed on a picture; the bar can be used for measurements on a picture. When the picture is resized the bar is resized making it possible to recalculate the magnification. Ideally, all pictures destined for publication/presentation should be supplied with a scale bar. All but one of the micrographs presented on this page do not have a micron bar.
The microscope has been used for scientific discovery. It has been linked to the arts since its invention in the 17th century. Early adopters of the microscope, such as Robert Hooke and Antonie van Leeuwenhoek, were excellent illustrators. After the invention of photography in the 1820s the microscope was combined with the camera to take pictures instead of relying on an artistic rendering. Since the early 1970s individuals have been using the microscope as an artistic instrument. Websites and traveling art exhibits such as the Nikon Small World and Olympus Bioscapes have featured a range of images for the sole purpose of artistic enjoyment; some collaborative groups, such as the Paper Project have incorporated microscopic imagery into tactile art pieces as well as 3D immersive rooms and dance performances. Close-up Digital microscope Macro photography Microphotograph Microscopy USB microscope Make a Micrograph – This presentation by the research department of Children's Hospital Boston shows how researchers create a three-color micrograph.
Shots with a Microscope – a basic, comprehensive guide to photomicrography Scientific photomicrographs – free scientific quality photomicrographs by Doc. RNDr. Josef Reischig, CSc. Micrographs of 18 natural fibres by the International Year of Natural Fibres 2009 Seeing Beyond the Human Eye Video produced by Off Book - Solomon C. Fuller bio Charles Krebs Microscopic Images Dennis Kunkel Microscopy Andrew Paul Leonard, APL Microscopic Cell Centered Database - Montage Nikon Small World Olympus Bioscapes Other examples
Breast
The breast is one of two prominences located on the upper ventral region of the torso of primates. In females, it serves as the mammary gland, which secretes milk to feed infants. Both females and males develop breasts from the same embryological tissues. At puberty, estrogens, in conjunction with growth hormone, cause breast development in female humans and to a much lesser extent in other primates. Breast development in other primate females only occurs with pregnancy. Subcutaneous fat covers and envelops a network of ducts that converge on the nipple, these tissues give the breast its size and shape. At the ends of the ducts are lobules, or clusters of alveoli, where milk is produced and stored in response to hormonal signals. During pregnancy, the breast responds to a complex interaction of hormones, including estrogens and prolactin, that mediate the completion of its development, namely lobuloalveolar maturation, in preparation of lactation and breastfeeding. Along with their major function in providing nutrition for infants, female breasts have social and sexual characteristics.
Breasts have been featured in notable ancient and modern sculpture and photography. They can figure prominently in the perception of a woman's body and sexual attractiveness. A number of Western cultures associate breasts with sexuality and tend to regard bare breasts in public as immodest or indecent. Breasts the nipples, are an erogenous zone; the English word breast derives from the Old English word brēost from Proto-Germanic breustam, from the Proto-Indo-European base bhreus–. The breast spelling conforms to the North English dialectal pronunciations; the Merriam-Webster Dictionary states. Old Irish brú, Russian bryukho". A large number of colloquial terms for breasts are used in English, ranging from polite terms to vulgar or slang; some vulgar slang expressions may be considered to be sexist to women. In women, the breasts overlie the pectoralis major muscles and extend from the level of the second rib to the level of the sixth rib in the front of the human rib cage. At the front of the chest, the breast tissue can extend from the clavicle to the middle of the sternum.
At the sides of the chest, the breast tissue can extend into the axilla, can reach as far to the back as the latissimus dorsi muscle, extending from the lower back to the humerus bone. As a mammary gland, the breast is composed of differing layers of tissue, predominantly two types: adipose tissue. Morphologically the breast is tear-shaped; the superficial tissue layer is separated from the skin by 0.5–2.5 cm of subcutaneous fat. The suspensory Cooper's ligaments are fibrous-tissue prolongations that radiate from the superficial fascia to the skin envelope; the female adult breast contains 14–18 irregular lactiferous lobes that converge at the nipple. The 2.0–4.5 mm milk ducts are surrounded with dense connective tissue that support the glands. Milk exits the breast through the nipple, surrounded by a pigmented area of skin called the areola; the size of the areola can vary among women. The areola contains modified sweat glands known as Montgomery's glands; these glands secrete oily fluid that protect the nipple during breastfeeding.
Volatile compounds in these secretions may serve as an olfactory stimulus for the newborn's appetite. The dimensions and weight of the breast vary among women. A small-to-medium-sized breast weighs 500 grams or less, a large breast can weigh 750 to 1,000 grams or more; the tissue composition ratios of the breast vary among women. Some women's breasts have varying proportions of glandular tissue than of adipose or connective tissues; the fat-to-connective-tissue ratio determines the firmness of the breast. During a woman's life, her breasts change size and weight due to hormonal changes during puberty, the menstrual cycle, pregnancy and menopause; the breast is an apocrine gland. The nipple of the breast is surrounded by the areola; the areola has many sebaceous glands, the skin color varies from pink to dark brown. The basic units of the breast are the terminal duct lobular units, which produce the fatty breast milk, they give the breast its offspring-feeding functions as a mammary gland. They are distributed throughout the body of the breast.
Two-thirds of the lactiferous tissue is within 30 mm of the base of the nipple. The terminal lactiferous ducts drain the milk from TDLUs into 4–18 lactiferous ducts, which drain to the nipple; the milk-glands-to-fat ratio is 2:1 in a lactating woman, 1:1 in a non-lactating woman. In addition to the milk glands, the breast is composed of connective tissues, white fat, the suspensory Cooper's ligaments. Sensation in the breast is provided by the peripheral nervous system innervation by means of the front and side cutaneous branches of the fourth-, fifth-, sixth intercostal nerves; the T-4 nerve, which innervates the dermatomic area, supplies sensation to the nipple-areola complex. 75% of the lymph from the breast travels to the axillary lymph nodes on the same side of the body, w
