Loose connective tissue
Loose connective tissue is a category of connective tissue which includes areolar tissue, reticular tissue, adipose tissue. Loose connective tissue is the most common type of connective tissue in vertebrates, it attaches epithelial tissue to other underlying tissues. For example, it forms telae, such as the tela submucosa and tela subserosa, which connect mucous and serous membranes to the muscular layer, it surrounds the blood vessels and nerves. Cells called fibroblasts are dispersed in this tissue; the cells of this type of tissue are separated by quite some distance by a gelatinous substance made up of collagenous and elastic fibers. "loose connective tissue" is considered a parent category that includes the mucous connective tissue of the fetus, areolar connective tissue, reticular connective tissue, adipose tissue. It is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs. Fibroblasts are dispersed in this tissue; the cells of this type of tissue are connected by a gelatinous substance known as ground substance made up of collagenous and elastic fibers.
It may be found in tissue sections from every part of the body. It surrounds blood vessels and nerves and penetrates with them into the small spaces of muscles and other tissues, it may be present in the mediastinal extremities. Nearly every epithelium rests on a layer of areolar tissue, whose blood vessels provide the epithelium with nutrition, waste removal, a ready supply of infection-fighting leukocytes when needed; because of the abundance of open, fluid-filled space, leukocytes can move about in areolar tissue and can find and destroy pathogens. The areolar tissue is found beneath the dermis layer and is underneath the epithelial tissue of all the body systems that have external openings, it is a component of the lamina propria of the digestive and respiratory tracts, the mucous membranes of reproductive and urinary systems, the stroma of glands, the hypodermis of the skin. It is found in the mesentery, surrounding the intestine. Loose connective tissue is named based on type of its constituent fibers.
There are three main types: Collagenous fibers: collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules. Elastic fibers: elastic fibers are made of elastin and are "stretchable." Reticular fibers: reticular fibers consist of one or more types of thin collagen fibers. They join connective tissues to other tissues. Areolar tissue is a common type of loose connective tissue, it is so named because its fibers are far enough apart to leave ample open space for interstitial fluid in between. It is strong enough to bind different tissue types together, yet soft enough to provide flexibility and cushioning, it exhibits interlacing, loosely organized fibers, abundant blood vessels, significant empty space filled with interstitial fluid. Many adjacent epithelial tissues get their nutrients from the interstitial fluid of areolar tissue, its fibers run in random directions and are collagenous, but elastic and reticular fibers are present. Areolar tissue is variable in appearance.
In many serous membranes, it appears as a loose arrangement of collagenous and elastic fibers, scattered cells of various types. In the skin and mucous membranes, it is more compact and sometimes difficult to distinguish from dense irregular connective tissue. Areolar connective tissues hold organs in place and attaches epithelial tissue to other underlying tissues, it serves as a reservoir of water and salts for surrounding tissues. All cells obtain their nutrients from and release their wastes into areolar connective tissue. Organs that are rich in loose connective tissue are sites that undergo oedema indicating renal failure or nephrotic syndrome, thus periorbital swelling is one characteristic finding in severe renal disease Dense connective tissue
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
Brown adipose tissue
Brown adipose tissue or brown fat makes up the adipose organ together with white adipose tissue. Brown adipose tissue is found in all mammals. Classification of brown fat refers to two distinct cell populations with similar functions; the first shares a common embryological origin with muscle cells, found in larger "classic" deposits. The second develops from white adipocytes; these adipocytes are found interspersed in white adipose tissue and are named'beige' or'brite'. Brown adipose tissue is abundant in newborns and in hibernating mammals, it is present and metabolically active in adult humans, but its prevalence decreases as humans age. Its primary function is thermoregulation. In addition to heat produced by shivering muscle, brown adipose tissue produces heat by non-shivering thermogenesis. In contrast to white adipocytes, which contain a single lipid droplet, brown adipocytes contain numerous smaller droplets and a much higher number of mitochondria, which gives the tissue its color. Brown fat contains more capillaries than white fat.
These supply the tissue with oxygen and distribute the produced heat throughout the body. The presence of brown adipose tissue in adult humans was discovered during FDG-PET scans to detect metastatic cancers. Using these scans and data from human autopsies, several brown adipose tissue depots have been identified. In infants, brown adipose tissue depots include, but are not limited to: interscapular, suprarenal, para-aortic and around the pancreas and trachea; these deposits get more white fat-like during adulthood. In adults, the depots that are most detected in FDG-PET scans are the supraclavicular, mediastinal, para-aortic and suprarenal ones, it remains to be determined whether these depots are'classical' brown adipose tissue or beige/brite fat. Brown fat in humans in the scientific and popular literature refers to two cell populations defined by both anatomical location and cellular morphology. Both share the presence of small lipid droplets and numerous iron-rich mitochondria, giving the brown appearance.
"Classical" brown fat is found in vascularized deposits in somewhat consistent anatomical locations, such as between the shoulder blades, surrounding the kidneys, the neck, supraclavicular area, along the spinal cord. This has numerous small lipid droplets. Beige fat is the adrenergically inducible cell type, dispersed throughout adipose tissue, it has greater variability in lipid droplet size and a greater proportion of lipid droplets to mitochondria giving it a light brown appearance. Brown fat cells come from the middle embryo layer, mesoderm the source of myocytes and chondrocytes; the classic population of brown fat cells and muscle cells both seem to be derived from the same population of stem cells in the mesoderm, paraxial mesoderm. Both have the intrinsic capacity to activate the myogenic factor 5 promoter, a trait only associated with myocytes and this population of brown fat. Progenitors of traditional white fat cells and adrenergically induced brown fat do not have the capacity to activate the Myf5 promoter.
Both adipocytes and brown adipocyte may be derived from pericytes, the cells which surround the blood vessels that run through white fat tissue. Notably, this is not the same as the presence of Myf5 protein, involved in the development of many tissues. Additionally, muscle cells that were cultured with the transcription factor PRDM16 were converted into brown fat cells, brown fat cells without PRDM16 were converted into muscle cells; the mitochondria in a eukaryotic cell utilize fuels to produce energy in the form of adenosine triphosphate. This process involves storing energy as a proton gradient known as the proton motive force, across the mitochondrial inner membrane; this energy is used to synthesize ATP when the protons flow across the membrane through the ATP synthase enzyme. In endotherms, body heat is maintained by signaling the mitochondria to allow protons to run back along the gradient without producing ATP; this can occur since an alternative return route for the protons exists through an uncoupling protein in the inner membrane.
This protein, known as uncoupling protein 1, facilitates the return of the protons after they have been pumped out of the mitochondria by the electron transport chain. This alternative route for protons uncouples oxidative phosphorylation and the energy in the PMF is instead released as heat. To some degree, all cells of endotherms give off heat when body temperature is below a regulatory threshold. However, brown adipose tissue is specialized for this non-shivering thermogenesis. First, each cell has a higher number of mitochondria compared to more typical cells. Second, these mitochondria have a higher-than-normal concentration of thermogenin in the inner membrane. In neonates, brown fat makes up about 5% of the body mass and is located on the back, along the upper half of the spine and toward the shoulders, it is of great importance to avoid hypothermia, as lethal cold is a major death risk for premature neonates. Numerous factors make infants more susceptible to cold than adults: A higher ratio of body surface area to body volume A higher proportional surface area of the head A low amount of musculature and the inability to shiver A lack of thermal insulation, e.g. subcutaneous fat and fine body hair (especially
A ligament is the fibrous connective tissue that connects bones to other bones. It is known as articular ligament, articular larua, fibrous ligament, or true ligament. Other ligaments in the body include the: Peritoneal ligament: a fold of peritoneum or other membranes. Fetal remnant ligament: the remnants of a fetal tubular structure. Periodontal ligament: a group of fibers that attach the cementum of teeth to the surrounding alveolar bone. Ligaments are similar to tendons and fasciae; the differences in them are in the connections that they make: ligaments connect one bone to another bone, tendons connect muscle to bone, fasciae connect muscles to other muscles. These are all found in the skeletal system of the human body. Ligaments cannot be regenerated naturally; the study of ligaments is known as desmology. "Ligament" most refers to a band of dense regular connective tissue bundles made of collagenous fibers, with bundles protected by dense irregular connective tissue sheaths. Ligaments connect bones to other bones to form joints.
Some ligaments prevent certain movements altogether. Capsular ligaments are part of the articular capsule, they act as mechanical reinforcements. Extra-capsular ligaments join together in harmony with the other ligaments and provide joint stability. Intra-capsular ligaments, which are much less common provide stability but permit a far larger range of motion. Cruciate ligaments are paired ligaments in the form of a cross. Ligaments are viscoelastic, they strain when under tension and return to their original shape when the tension is removed. However, they cannot retain their original shape when extended past a certain point or for a prolonged period of time; this is one reason why dislocated joints must be set as as possible: if the ligaments lengthen too much the joint will be weakened, becoming prone to future dislocations. Athletes, gymnasts and martial artists perform stretching exercises to lengthen their ligaments, making their joints more supple; the term hypermobility refers to people with more-elastic ligaments, allowing their joints to stretch and contort further.
The consequence of a broken ligament can be instability of the joint. Not all broken ligaments need surgery, but, if surgery is needed to stabilise the joint, the broken ligament can be repaired. Scar tissue may prevent this. If it is not possible to fix the broken ligament, other procedures such as the Brunelli procedure can correct the instability. Instability of a joint can over time lead to wear of the cartilage and to osteoarthritis. One of the most torn ligaments in the body is the anterior cruciate ligament; the ACL is one of the ligaments crucial to knee stability and persons who tear their ACL seek to undergo reconstructive surgery, which can be done through a variety of techniques and materials. One of these techniques is the replacement of the ligament with an artificial material. An artificial ligament is a reinforcing material, used to replace a torn ligament, such as the ACL. Artificial ligaments are a synthetic material composed of a polymer, such as polyacrylonitrile fiber, polypropylene, PET, or polyNaSS poly.
Certain folds of peritoneum are referred to as ligaments. Examples include: The hepatoduodenal ligament, that surrounds the hepatic portal vein and other vessels as they travel from the duodenum to the liver; the broad ligament of the uterus a fold of peritoneum. Certain tubular structures from the fetal period are referred to as ligaments after they close up and turn into cord-like structures: Broström procedure
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
Dense connective tissue
Dense connective tissue called dense fibrous tissue, is a type of connective tissue with fibers as its main matrix element. The fibers are composed of type I collagen. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that generate the fibers. Dense connective tissue forms rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones. Ligaments contain more elastic fibers than tendons. Dense connective tissue make up the lower layers of the skin, where it is arranged in sheets, it is classified as dense irregular connective tissue. Loose connective tissue Anatomy photo: TermsCells&Tissues/connective/dense/dense1 - Comparative Organology at University of California, Davis - "Connective tissue, dense" Histology at cytochemistry.net Overview at downstate.edu
White adipose tissue
White adipose tissue or white fat is one of the two types of adipose tissue found in mammals. The other kind is brown adipose tissue. In healthy, non-overweight humans, white adipose tissue composes as much as 20% of the body weight in men and 25% in women, its cells contain a single large fat droplet, which forces the nucleus to be squeezed into a thin rim at the periphery. They have receptors for insulin, sex hormones and glucocorticoids. White adipose tissue is used for energy storage. Upon release of insulin from the pancreas, white adipose cells' insulin receptors cause a dephosphorylation cascade that lead to the inactivation of hormone-sensitive lipase, it was thought that upon release of glucagon from the pancreas, glucagon receptors cause a phosphorylation cascade that activates hormone-sensitive lipase, causing the breakdown of the stored fat to fatty acids, which are exported into the blood and bound to albumin, glycerol, exported into the blood freely. There is no evidence at present that glucagon has any effect on lipolysis in white adipose tissue.
Glucagon is now thought to act on the liver to trigger glycogenolysis and gluconeogenesis. The trigger for this process in white adipose tissue is instead now thought to be adrenocorticotropic hormone and noradrenaline. Fatty acids are taken up by muscle and cardiac tissue as a fuel source, glycerol is taken up by the liver for gluconeogenesis. White adipose tissue acts as a thermal insulator, helping to maintain body temperature; the hormone leptin is manufactured in the adipocytes of white adipose tissue which produces another hormone, asprosin. Location---mainly found behind eyeball, omenta, mesentry and whale blubbers, hump of a camel, yellow bone marrow, fat bodies of frogs, tail of Marino sheep, hypodermis of skin