Anatomical terms of microanatomy
Anatomical terminology is used to describe microanatomical structures. This helps describe the structure and position of an object, minimises ambiguity. An internationally accepted lexicon is Terminologia Histologica. Epithelial cells line body surfaces, are described according to their shape, with three principal shapes: squamous and cuboidal. Squamous epithelium has cells. Cuboidal epithelium has cells whose height and width are the same. Columnar epithelium has cells taller. Endothelium refers to cells that line the interior surface of blood vessels and lymphatic vessels, forming an interface between circulating blood or lymph in the lumen and the rest of the vessel wall, it is a thin layer of single-layered, squamous cells called endothelial cells. Endothelial cells in direct contact with blood are called vascular endothelial cells, whereas those in direct contact with lymph are known as lymphatic endothelial cells. Epithelium can be arranged in a single layer of cells described as "simple", or more than one layer, described as "stratified".
By layer, epithelium is classed as either simple epithelium, only one cell thick or stratified epithelium as stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium that are two or more cells thick, both types of layering can be made up of any of the cell shapes. However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia; this kind of epithelium is therefore described as pseudostratified columnar epithelium. Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium. A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of internal organs, it consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is of endodermal origin and is continuous with the skin at various body openings such as the eyes, inside the nose, inside the mouth, the urethral opening and the anus.
Some mucous membranes a thick protective fluid. The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated; the submucosa consists of a dense and irregular layer of connective tissue with blood vessels and nerves branching into the mucosa and muscular layer. It contains the submucous plexus, enteric nervous plexus, situated on the inner surface of the muscular layer; the muscular layer consists of two layers of the inner and outer layer. The muscle of the inner layer is arranged in circular rings around the tract, whereas the muscle of the outer layer is arranged longitudinally; the stomach has an inner oblique muscular layer. Between the two muscle layers are the myenteric or Auerbach's plexus; this controls peristalsis. Activity is initiated by the pacemaker cells; the gut has intrinsic peristaltic activity due to its self-contained enteric nervous system. The rate can of course be modulated by the rest of the autonomic nervous system.
The layers are not longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. Serosa / Adventitia -- these last two tissue types differ in form and function according to the part of the gastrointestinal tract they belong to; the hollow inner part of a body organ or tube is called the lumen. The side of a cell facing the lumen is called the apical surface.
Collagen is the main structural protein in the extracellular space in the various connective tissues in the body. As the main component of connective tissue, it is the most abundant protein in mammals, making 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple-helices of elongated fibrils, it is found in fibrous tissues such as tendons and skin. Depending upon the degree of mineralization, collagen tissues may be rigid, compliant, or have a gradient from rigid to compliant, it is abundant in corneas, blood vessels, the gut, intervertebral discs, the dentin in teeth. 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, muscles; the fibroblast is the most common cell. Gelatin, used in food and industry, is collagen that has been, hydrolyzed. Collagen has many medical uses in treating complications of skin; the name collagen comes from the Greek κόλλα, meaning "glue", suffix -γέν, -gen, denoting "producing".
This refers to the compound's early use in the process of boiling the skin and tendons of horses and other animals to obtain glue. Over 90% of the collagen in the human body is type I. However, as of 2011, 28 types of collagen have been identified and divided into several groups according to the structure they form: Fibrillar Non-fibrillar FACIT Short chain Basement membrane Multiplexin MACIT Other The five most common types are: Type I: skin, vasculature, bone Type II: cartilage Type III: reticulate found alongside type I Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane Type V: cell surfaces and placenta The collagenous cardiac skeleton which includes the four heart valve rings, is histologically and uniquely bound to cardiac muscle; the cardiac skeleton includes the separating septa of the heart chambers – the interventricular septum and the atrioventricular 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.
The collagenous structure that divides the upper chambers of the heart from the lower chambers is an impermeable membrane that excludes both blood and electrical impulses through typical physiological means. With support from collagen, atrial fibrillation never deteriorates to ventricular fibrillation. Collagen is layered in variable densities with cardiac muscle mass; the mass, distribution and density of collagen all contribute to the compliance required to move blood back and forth. 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. Calcified points within collagen matrices show contrast in a moving display of blood and muscle, enabling methods of cardiac imaging technology to arrive at ratios stating blood in and blood out. Pathology of the collagen 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 and surgical purposes.
Both human and bovine collagen is used as dermal fillers for treatment of wrinkles and skin aging. Some points of interest are: When used cosmetically, there is a chance of allergic reactions causing prolonged redness. Most medical collagen is derived from young beef cattle from certified BSE-free animals. Most manufacturers use donor animals from either "closed herds", or from countries which have never had a reported case of BSE such as Australia and New Zealand; as the skeleton forms the structure of the body, it is vital that it maintains its strength after breaks and injuries. Collagen is used in bone grafting as it has a triple helical structure, making it a strong molecule, it is ideal for use in bones. The triple helical structure of collagen prevents it from being broken down by enzymes, it enables adhesiveness of cells and it is important for the proper assembly of the extracellular matrix. Collagen scaffolds are used in tissue regeneration, whether in thin sheets, or gels. Collagen has the correct properties for tissue regeneration such as pore structure, permeability and being stable in vivo.
Collagen scaffolds are ideal for the deposition of cells such as osteoblasts and fibroblasts, once inserted, growth is able to continue as normal in the tissue. Collagens are employed in the construction of the artificial skin substitutes used in the management of severe burns and wounds; these collagens may be derived from bovine, porcine, or human sources. Collagen is one of the body’s key natural resources and a component of skin tissu
The submucosa is a thin layer of tissue in various organs of the gastrointestinal and genitourinary tracts. It is the layer of dense irregular connective tissue that supports the mucosa and joins it to the muscular layer, the bulk of overlying smooth muscle; the submucosa is to a mucous membrane. Blood vessels, lymphatic vessels, nerves will run through here. Tiny parasympathetic ganglia are scattered around forming the submucosal plexus where preganglionic parasympathetic neurons synapse with postganglionic nerve fibers that supply the muscularis mucosae. Histologically, the wall of the alimentary canal shows four distinct layers: mucosa, muscularis externa, a serosa or adventitia. Identification of the submucosa plays an important role in diagnostic and therapeutic endoscopy, where special fibre-optic cameras are used to perform procedures on the gastrointestinal tract. Abnormalities of the submucosa, such as gastrointestinal stromal tumors show integrity of the mucosal surface; the submucosa is identified in endoscopic ultrasound to identify the depth of tumours and to identify other abnormalities.
An injection of dye, saline, or epinephrine into the submucosa is imperative in the safe removal of certain polyps. Endoscopic mucosal resection involves removal of the mucosal layer, in order to be done safely, a submucosal injection of dye is performed to ensure integrity at the beginning of the procedure. Female uterine submucosal layers are liable to develop fibroids during pregnancy and are excised upon discovery. Small intestinal submucosa is submucosal tissue in the small intestines of vertebrates. SIS is harvested for transplanted structural material in several clinical applications biologic meshes, they have low immunogenicity. Some uses under investigation include a scaffold for intervertebral disc regeneration. Unlike other scaffold materials, the resorbable SIS extracellular matrix scaffold is replaced by well-organized host tissues, including differentiated skeletal muscle. A scientific article published in March 2018 proposed a revision of the anatomical definition of the submucosa.
They first saw a non compact tissue which should be submucosa using a technology called endomicroscopy. They hypothesised that the submucosa was not compact as it was seen on histological analysis but form a reticular pattern. To confirm their findings, they performed fixed samples of bile duct into a freezing media in order to conserve the shape of the submucosa, they performed a histological analysis and with several staining technics, they described the submucosa as a network of collagenous bands separating open fluid-filled spaces. Theses spaces are bordered by fibroblast-like cells CD34 positive. However, these cells are devoid of ultrastructural features indicative of endothelial differentiation, including pinocytotic vesicles and Weibel-Palade bodies
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; this network acts as a supporting mesh in soft tissues such as liver, bone marrow, 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. However, during the pre-molecular era, there was confusion in the use of the term reticulin, used to describe two structures: the argyrophilic fibrous structures present in basement membranes histologically similar fibers present in developing connective tissue; the history of the reticulin silver stain is reviewed by Puchtler et al.. The abstract of this paper says: Maresch introduced Bielschowsky's silver impregnation technic for neurofibrils as a stain for reticulum fibers, but emphasized the nonspecificity of such procedures.
This lack of specificity has been confirmed repeatedly. Yet, since the 1920s the definition of "reticulin" and studies of its distribution were based on silver impregnation technics; the chemical mechanism and specificity of this group of stains is obscure. Application of Gömöri's and Wilder's methods to human tissues showed variations of staining patterns with the fixatives and technics employed. Besides reticulum fibers, various other tissue structures, e.g. I bands of striated muscle, fibers in nervous tissues, model substances, e.g. polysaccharides, egg white, were stained. Deposition of silver compounds on reticulum fibers was limited to an removable substance; these histochemical studies indicate that silver impregnation technics for reticulum fibers have no chemical significance and cannot be considered as histochemical technics for "reticulin" or type III collagen. Reticular fiber is composed of one or more types of thin and delicately woven strands of type III collagen; these strands build a 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; the 1953 Science article mentioned above concluded that the reticular and regular collagenous materials contains the same four sugars – galactose, glucose and fucose – but in a much greater concentration in the reticular than in the collagenous material. In a 1993 paper, the reticular fibers of the capillary sheath and splenic cord were studied and compared in the pig spleen by transmission electron microscopy; this paper attempted to reveal their components and the presence of sialic acid in the amorphous ground substance. Collagen fibrils, elastic fibers, nerve fibers, smooth muscle cells were observed in the reticular fibers of the splenic cord. On the other hand, only microfibrils were recognized in the reticular fibers of the capillary sheath; the binding of LFA lectin to the splenic cord was stronger than the capillary sheath.
These findings suggested that the reticular fibers of the splenic cord include multiple functional elements and might perform an important role during contraction or dilation of the spleen. On the other hand, the reticular 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
In biology, adipose tissue, body fat, or fat is a loose connective tissue composed of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction of cells including preadipocytes, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Adipose tissue is derived from preadipocytes, its main role is to store energy in the form of lipids, although it cushions and insulates the body. Far from being hormonally inert, adipose tissue has, in recent years, been recognized as a major endocrine organ, as it produces hormones such as leptin, estrogen and the cytokine TNFα; the two types of adipose tissue are white adipose tissue, which stores energy, brown adipose tissue, which generates body heat. The formation of adipose tissue appears to be controlled in part by the adipose gene. Adipose tissue – more brown adipose tissue – was first identified by the Swiss naturalist Conrad Gessner in 1551. In humans, adipose tissue is located: beneath the skin, around internal organs, in bone marrow, intermuscular and in the breast tissue.
Adipose tissue is found in specific locations, which are referred to as adipose depots. Apart from adipocytes, which comprise the highest percentage of cells within adipose tissue, other cell types are present, collectively termed stromal vascular fraction of cells. SVF includes preadipocytes, adipose tissue macrophages, endothelial cells. Adipose tissue contains many small blood vessels. In the integumentary system, which includes the skin, it accumulates in the deepest level, the subcutaneous layer, providing insulation from heat and cold. Around organs, it provides protective padding. However, its main function is to be a reserve of lipids, which can be oxidised to meet the energy needs of the body and to protect it from excess glucose by storing triglycerides produced by the liver from sugars, although some evidence suggests that most lipid synthesis from carbohydrates occurs in the adipose tissue itself. Adipose depots in different parts of the body have different biochemical profiles. Under normal conditions, it provides feedback for hunger and diet to the brain.
Mice have eight major adipose depots, four of which are within the abdominal cavity. The paired gonadal depots are attached to the uterus and ovaries in females and the epididymis and testes in males; the mesenteric depot forms a glue-like web that supports the intestines and the omental depot and - when massive - extends into the ventral abdomen. Both the mesenteric and omental depots incorporate much lymphoid tissue as lymph nodes and milky spots, respectively; the two superficial depots are the paired inguinal depots, which are found anterior to the upper segment of the hind limbs and the subscapular depots, paired medial mixtures of brown adipose tissue adjacent to regions of white adipose tissue, which are found under the skin between the dorsal crests of the scapulae. The layer of brown adipose tissue in this depot is covered by a "frosting" of white adipose tissue; the inguinal depots enclose the inguinal group of lymph nodes. Minor depots include the pericardial, which surrounds the heart, the paired popliteal depots, between the major muscles behind the knees, each containing one large lymph node.
Of all the depots in the mouse, the gonadal depots are the largest and the most dissected, comprising about 30% of dissectible fat. In an obese person, excess adipose tissue hanging downward from the abdomen is referred to as a panniculus. A panniculus complicates surgery of the morbidly obese individual, it may remain as a literal "apron of skin" if a obese person loses large amounts of fat. This condition cannot be corrected through diet and exercise alone, as the panniculus consists of adipocytes and other supporting cell types shrunken to their minimum volume and diameter. Reconstructive surgery is one method of treatment. Visceral fat or abdominal fat is located inside the abdominal cavity, packed between the organs. Visceral fat is different from subcutaneous fat underneath the skin, intramuscular fat interspersed in skeletal muscles. Fat in the lower body, as in thighs and buttocks, is subcutaneous and is not spaced tissue, whereas fat in the abdomen is visceral and semi-fluid. Visceral fat is composed of several adipose depots, including mesenteric, epididymal white adipose tissue, perirenal depots.
Visceral fat is expressed in terms of its area in cm2. An excess of visceral fat is known as central obesity, or "belly fat", in which the abdomen protrudes excessively. New developments such as the Body Volume Index are designed to measure abdominal volume and abdominal fat. Excess visceral fat is linked to type 2 diabetes, insulin resistance, inflammatory diseases, other obesity-related diseases; the accumulation of neck fat has been shown to be associated with mortality. Several studies have suggested that visceral fat can be predicted from simple anthropometric measures, predicts mortality more than body mass index or waist circumference. Men are more to have fat stored in the abdomen due to sex hormone differences. Female sex hor
Skin is the soft outer tissue covering of vertebrates with three main functions: protection and sensation. Other animal coverings, such as the arthropod exoskeleton, have different developmental origin and chemical composition; the adjective cutaneous means "of the skin". In mammals, the skin is an organ of the integumentary system made up of multiple layers of ectodermal tissue, guards the underlying muscles, bones and internal organs. Skin of a different nature exists in amphibians and birds. All mammals have some hair on their skin marine mammals like whales and porpoises which appear to be hairless; the skin is the first line of defense from external factors. For example, the skin plays a key role in protecting the body against pathogens and excessive water loss, its other functions are insulation, temperature regulation and the production of vitamin D folates. Damaged skin may heal by forming scar tissue; this is sometimes depigmented. The thickness of skin varies from location to location on an organism.
In humans for example, the skin located under the eyes and around the eyelids is the thinnest skin in the body at 0.5 mm thick, is one of the first areas to show signs of aging such as "crows feet" and wrinkles. The skin on the palms and the soles of the feet is the thickest skin on the body; the speed and quality of wound healing in skin is promoted by the reception of estrogen. Fur is dense hair. Fur augments the insulation the skin provides but can serve as a secondary sexual characteristic or as camouflage. On some animals, the skin is hard and thick, can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier regarding the passage of chemicals via skin and is subject to osmosis and diffusive forces. For example, a frog sitting in an anesthetic solution would be sedated as the chemical diffuses through its skin. Amphibian skin plays key roles in everyday survival and their ability to exploit a wide range of habitats and ecological conditions.
Mammalian skin is composed of two primary layers: the epidermis, which provides waterproofing and serves as a barrier to infection. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing pathogens from entering, is a stratified squamous epithelium, composed of proliferating basal and differentiated suprabasal keratinocytes. Keratinocytes are the major cells, constituting 95% of the epidermis, while Merkel cells and Langerhans cells are present; the epidermis can be further subdivided into the following strata or layers: Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum germinativum Keratinocytes in the stratum basale proliferate through mitosis and the daughter cells move up the strata changing shape and composition as they undergo multiple stages of cell differentiation to become anucleated. During that process, keratinocytes will become organized, forming cellular junctions between each other and secreting keratin proteins and lipids which contribute to the formation of an extracellular matrix and provide mechanical strength to the skin.
Keratinocytes from the stratum corneum are shed from the surface. The epidermis contains no blood vessels, cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis; the epidermis and dermis are separated by a thin sheet of fibers called the basement membrane, made through the action of both tissues. The basement membrane controls the traffic of the cells and molecules between the dermis and epidermis but serves, through the binding of a variety of cytokines and growth factors, as a reservoir for their controlled release during physiological remodeling or repair processes; the dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis provides tensile strength and elasticity to the skin through an extracellular matrix composed of collagen fibrils and elastic fibers, embedded in hyaluronan and proteoglycans. Skin proteoglycans are varied and have specific locations.
For example, hyaluronan and decorin are present throughout the dermis and epidermis extracellular matrix, whereas biglycan and perlecan are only found in the epidermis. It harbors many mechanoreceptors that provide the sense of touch and heat through nociceptors and thermoreceptors, it contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as for the epidermis; the dermis is connected to the epidermis through a basement membrane and is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary region, a deep thicker area known as the reticular region. The papillary region is composed of loose areolar connective tissue; this is named for its fingerlike projections called papillae. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the tw
Adipocytes known as lipocytes and fat cells, are the cells that compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes, osteoblasts and other cell types through adipogenesis. There are two types of adipose tissue, white adipose tissue and brown adipose tissue, which are known as white fat and brown fat and comprise two types of fat cells. White fat cells or monovacuolar cells contain a large lipid droplet surrounded by a layer of cytoplasm; the nucleus is located on the periphery. A typical fat cell is 0.1 mm in diameter with some being others half that size. The fat stored is in a semi-liquid state, is composed of triglycerides and cholesteryl ester. White fat cells secrete many proteins acting as adipokines such as resistin, adiponectin and apelin. An average human adult has 30 billion fat cells with a weight of 13.5 kg. If excess weight is gained as an adult, fat cells increase in size about fourfold before dividing and increasing the absolute number of fat cells present.
Brown fat cells or plurivacuolar cells are polyhedral in shape. Unlike white fat cells, these cells have considerable cytoplasm, with lipid droplets scattered throughout; the nucleus is round, although eccentrically located, it is not in the periphery of the cell. The brown color comes from the large quantity of mitochondria. Brown fat known as "baby fat," is used to generate heat. Marrow adipocytes, like white adipocytes, are derived from mesenchymal stem cells; the marrow adipose tissue depot is poorly understood in terms of its physiologic function and relevance to bone health. Marrow adipose tissue expands in states of low bone density but additionally expands in the setting of obesity. Marrow adipose tissue response to exercise approximates that of WAT exercise reduces both adipocyte size as well as MAT volume as quantified by MRI or μCT imaging of bone stained with the lipid binder osmium. Pre-adipocytes are undifferentiated fibroblasts. Recent studies shed light into potential molecular mechanisms in the fate determination of pre-adipocytes although the exact lineage of adipocyte is still unclear.
The variation of body fat distribution resulting from normal growth is influenced by nutritional and hormonal status in dependence on intrinsic differences in cells found in each adipose depot. Mesenchymal stem cells can differentiate into connective tissue, muscle or bone; the term "lipoblast" is used to describe the precursor of the adult cell. The term "lipoblastoma" is used to describe a tumor of this cell type. Fat cells in some mice have been shown to drop in count due to fasting and other properties were observed when exposed to cold. If the adipocytes in the body reach their maximum capacity of fat, they may replicate to allow additional fat storage. Adult rats of various strains became obese when they were fed a palatable diet for several months. Analysis of their adipose tissue morphology revealed increases in both adipocyte size and number in most depots. Reintroduction of an ordinary chow diet to such animals precipitated a period of weight loss during which only mean adipocyte size returned to normal.
Adipocyte number remained at the elevated level achieved during the period of weight gain. In some reports and textbooks, the number of adipocytes can increase in childhood and adolescence, though the amount is constant in adults. Individuals who become obese as adults, rather than as adolescents, have no more adipocytes than they had before. People who have been fat since childhood have an inflated number of fat cells. People who become fat as adults may have no more fat cells than their lean peers, but their fat cells are larger. In general, people with an excess of fat cells find it harder to lose weight and keep it off than the obese who have enlarged fat cells. Body fat cells have regional responses to the overfeeding, studied in adult subjects. In the upper body, an increase of adipocyte size correlated with upper-body fat gain. In contrast to the upper body fat cell response, the number of lower-body adipocytes did increase during the course of experiment. Notably, there was no change in the size of the lower-body adipocytes.
10% of fat cells are renewed annually at all adult ages and levels of body mass index without a significant increase in the overall number of adipocytes in adulthood. Obesity is characterized by the expansion of fat mass, through adipocyte size increase and, to a lesser extent, cell proliferation. In the fat cells of obese individuals, there is increased production of metabolism modulators, such as glycerol, macrophage stimulating chemokines, pro-inflammatory cytokines, leading to the development of insulin resistance. Fat production in adipocytes is stimulated by insulin. By controlling the activity of the pyruvate dehydrogenase and the acetyl-CoA carboxylase enzymes, insulin promotes unsaturated fatty acid synthesis, it promotes glucose uptake and induces SREBF1, which activates the transcription of genes that stimulate lipogenesis. SREBF1 is a transcription factor synthesized as an inactive precursor protein inserted into the endoplasmic reticulum membrane by two membrane-spanning helices.
Anchored in the ER membrane is SCAP, which binds SREBF1. The SREBF1-SCAP complex is retained in the ER membrane by INSIG1; when sterol levels are depleted, INSIG1 releases SCAP and the SREBF1