Mucus is a polymer. It is a slippery aqueous secretion produced by, covering, mucous membranes, it is produced from cells found in mucous glands, although it may originate from mixed glands, which contain both serous and mucous cells. It is a viscous colloid containing inorganic salts, antiseptic enzymes and glycoproteins such as lactoferrin and mucins, which are produced by goblet cells in the mucous membranes and submucosal glands. Mucus serves to protect epithelial cells in the respiratory, urogenital and auditory systems. Most of the mucus produced is in the gastrointestinal tract. Bony fish, snails and some other invertebrates produce external mucus. In addition to serving a protective function against infectious agents, such mucus provides protection against toxins produced by predators, can facilitate movement and may play a role in communication. In the human respiratory system, mucus known as airway surface liquid, aids in the protection of the lungs by trapping foreign particles that enter them, in particular, through the nose, during normal breathing.
Further distinction exists between the superficial and cell-lining layers of ASL, which are known as mucus layer and pericilliary liquid layer, respectively. "Phlegm" is a specialized term for mucus, restricted to the respiratory tract, whereas the term "nasal mucus" describes secretions of the nasal passages. Nasal mucus is produced by the nasal mucosa. Small particles such as dust, particulate pollutants, allergens, as well as infectious agents and bacteria are caught in the viscous nasal or airway mucus and prevented from entering the system; this event along with the continual movement of the respiratory mucus layer toward the oropharynx, helps prevent foreign objects from entering the lungs during breathing. This explains why coughing occurs in those who smoke cigarettes; the body's natural reaction is to increase mucus production. In addition, mucus aids in moisturizing the inhaled air and prevents tissues such as the nasal and airway epithelia from drying out. Nasal and airway mucus is produced continuously, with most of it swallowed subconsciously when it is dried.
Increased mucus production in the respiratory tract is a symptom of many common illnesses, such as the common cold and influenza. Hypersecretion of mucus can occur in inflammatory respiratory diseases such as respiratory allergies and chronic bronchitis; the presence of mucus in the nose and throat is normal, but increased quantities can impede comfortable breathing and must be cleared by blowing the nose or expectorating phlegm from the throat. In general, nasal mucus is thin, serving to filter air during inhalation. During times of infection, mucus can change color to yellow or green either as a result of trapped bacteria or due to the body's reaction to viral infection; the green color of mucus comes from the heme group in the iron-containing enzyme myeloperoxidase secreted by white blood cells as a cytotoxic defense during a respiratory burst. In the case of bacterial infection, the bacterium becomes trapped in already-clogged sinuses, breeding in the moist, nutrient-rich environment. Sinusitis is an uncomfortable condition.
A bacterial infection in sinusitis will cause discolored mucus and would respond to antibiotic treatment. All sinusitis infections are viral and antibiotics are ineffective and not recommended for treating typical cases. In the case of a viral infection such as cold or flu, the first stage and the last stage of the infection cause the production of a clear, thin mucus in the nose or back of the throat; as the body begins to react to the virus, mucus may turn yellow or green. Viral infections cannot be treated with antibiotics, are a major avenue for their misuse. Treatment is symptom-based. Increased mucus production in the upper respiratory tract is a symptom of many common ailments, such as the common cold. Nasal mucus may be removed by using nasal irrigation. Excess nasal mucus, as with a cold or allergies, due to vascular engorgement associated with vasodilation and increased capillary permeability caused by histamines, may be treated cautiously with decongestant medications. Thickening of mucus as a "rebound" effect following overuse of decongestants may produce nasal or sinus drainage problems and circumstances that promote infection.
During cold, dry seasons, the mucus lining nasal passages tends to dry out, meaning that mucous membranes must work harder, producing more mucus to keep the cavity lined. As a result, the nasal cavity can fill up with mucus. At the same time, when air is exhaled, water vapor in breath condenses as the warm air meets the colder outside temperature near the nostrils; this causes an excess amount of water to build up inside nasal cavities. In these cases, the excess fluid spills out externally through the nostrils. Excess mucus production in the bronchi and bronchioles, as may occur in asthma, bronchitis or influenza, results from chronic airway inflammation, hence may be treated with anti-inflammatory medications. Impaired mucociliary clearance due to conditions such as primary ciliary dyskinesia may result in its accumulation in the bronchi; the dysregulation of
Epigenetics is the study of heritable phenotype changes that do not involve alterations in the DNA sequence. The Greek prefix epi- in epigenetics implies features that are "on top of" or "in addition to" the traditional genetic basis for inheritance. Epigenetics most denotes changes that affect gene activity and expression, but can be used to describe any heritable phenotypic change; such effects on cellular and physiological phenotypic traits may result from external or environmental factors, or be part of normal development. The standard definition of epigenetics requires these alterations to be heritable, either in the progeny of cells or of organisms; the term refers to the changes themselves: functionally relevant changes to the genome that do not involve a change in the nucleotide sequence. Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence. Gene expression can be controlled through the action of repressor proteins that attach to silencer regions of the DNA.
These epigenetic changes may last through cell divisions for the duration of the cell's life, may last for multiple generations though they do not involve changes in the underlying DNA sequence of the organism. One example of an epigenetic change in eukaryotic biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become differentiated cells. In other words, as a single fertilized egg cell – the zygote – continues to divide, the resulting daughter cells change into all the different cell types in an organism, including neurons, muscle cells, endothelium of blood vessels, etc. by activating some genes while inhibiting the expression of others. Some phenomena not heritable have been described as epigenetic. For example, the term epigenetic has been used to describe any modification of chromosomal regions histone modifications, whether or not these changes are heritable or associated with a phenotype.
The consensus definition now requires a trait to be heritable. The term epigenetics in its contemporary usage emerged in the 1990s, but for some years has been used in somewhat variable meanings. A consensus definition of the concept of epigenetic trait as "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence" was formulated at a Cold Spring Harbor meeting in 2008, although alternate definitions that include non-heritable traits are still being used; the term epigenesis has a generic meaning "extra growth". It has been used in English since the 17th century. From the generic meaning, the associated adjective epigenetic, C. H. Waddington coined the term epigenetics in 1942 as pertaining to epigenesis, in parallel to Valentin Haecker's'phenogenetics'. Epigenesis in the context of the biology of that period referred to the differentiation of cells from their initial totipotent state in embryonic development; when Waddington coined the term, the physical nature of genes and their role in heredity was not known.
Waddington held that cell fates were established in development much as a marble rolls down to the point of lowest local elevation. Waddington suggested visualising increasing irreversibility of cell type differentiation as ridges rising between the valleys where the marbles are travelling. In recent times Waddington's notion of the epigenetic landscape has been rigorously formalized in the context of the systems dynamics state approach to the study of cell-fate. Cell-fate determination is predicted to exhibit certain dynamics, such as attractor-convergence or oscillatory; the term "epigenetic" has been used in developmental psychology to describe psychological development as the result of an ongoing, bi-directional interchange between heredity and the environment. Interactivist ideas of development have been discussed in various forms and under various names throughout the 19th and 20th centuries. An early version was proposed, among the founding statements in embryology, by Karl Ernst von Baer and popularized by Ernst Haeckel.
A radical epigenetic view was developed by Paul Wintrebert. Another variation, probabilistic epigenesis, was presented by Gilbert Gottlieb in 2003; this view encompasses all of the possible developing factors on an organism and how they not only influence the organism and each other, but how the organism influences its own development. The developmental psychologist Erik Erikson wrote of an epigenetic principle in his book Identity: Youth and Crisis, encompassing the notion that we develop through an unfolding of our personality in predetermined stages, that our environment and surrounding culture influence how we progress through these stages; this biological unfolding in relation to our socio-cultural settings is done in stages of psychosocial development, where "progress through each stage is in part determined by our success, or lack of success, in all the previous stages." Robin Holliday defined epigenetics as "the study of the mechanisms of temporal and spatial control of gene activity during the development of complex organisms."
Thus epigenetic can be used to describe anything other than DNA s
Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, alpha-hemolytic or beta-hemolytic, facultative anaerobic member of the genus Streptococcus. They are found in pairs and do not form spores and are nonmotile; as a significant human pathogenic bacterium S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century, is the subject of many humoral immunity studies. S. pneumoniae resides asymptomatically in healthy carriers colonizing the respiratory tract and nasal cavity. However, in susceptible individuals with weaker immune systems, such as the elderly and young children, the bacterium may become pathogenic and spread to other locations to cause disease, it spreads by direct person-to-person contact via respiratory droplets and by autoinoculation in persons carrying the bacteria in their upper respiratory tracts. It can be a cause of neonatal infections. S. Pneumoniae is the main cause of community acquired pneumonia and meningitis in children and the elderly, of septicemia in those infected with HIV.
The organism causes many types of pneumococcal infections other than pneumonia. These invasive pneumococcal diseases include bronchitis, acute sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, peritonitis, pericarditis and brain abscess. S. Pneumoniae can be differentiated from the viridans streptococci, some of which are alpha-hemolytic, using an optochin test, as S. pneumoniae is optochin-sensitive. S. pneumoniae can be distinguished based on its sensitivity to lysis by bile, the so-called "bile solubility test". The encapsulated, Gram-positive, coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci, they have a polysaccharide capsule. In 1881, the organism, known in 1886 as the pneumococcus for its role as a cause of pneumonia, was first isolated and independently by the U. S. Army physician the French chemist Louis Pasteur; the organism was termed Diplococcus pneumoniae from 1920 because of its characteristic appearance in Gram-stained sputum.
It was renamed Streptococcus pneumoniae in 1974 because it was similar to streptococci. S. Pneumoniae played a central role in demonstrating that genetic material consists of DNA. In 1928, Frederick Griffith demonstrated transformation of life turning harmless pneumococcus into a lethal form by co-inoculating the live pneumococci into a mouse along with heat-killed virulent pneumococci. In 1944, Oswald Avery, Colin MacLeod, Maclyn McCarty demonstrated that the transforming factor in Griffith's experiment was not protein, as was believed at the time, but DNA. Avery's work marked the birth of the molecular era of genetics; the genome of S. pneumoniae is a closed, circular DNA structure that contains between 2.0 and 2.1 million base pairs depending on the strain. It has a core set of 1553 genes, plus 154 genes in its virulome, which contribute to virulence and 176 genes that maintain a noninvasive phenotype. Genetic information can vary up to 10% between strains. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the surrounding medium.
Transformation is a complex developmental process requiring energy and is dependent on expression of numerous genes. In S. pneumoniae, at least 23 genes are required for transformation. For a bacterium to bind, take up, recombine exogenous DNA into its chromosome, it must enter a special physiological state called competence. Competence in S. pneumoniae is induced by DNA-damaging agents such as mitomycin C, fluoroquinolone antibiotics, topoisomerase inhibitors. Transformation protects S. pneumoniae against the bactericidal effect of mitomycin C. Michod et al. summarized evidence that induction of competence in S. pneumoniae is associated with increased resistance to oxidative stress and increased expression of the RecA protein, a key component of the recombinational repair machinery for removing DNA damages. On the basis of these findings, they suggested that transformation is an adaptation for repairing oxidative DNA damages. S. pneumoniae infection stimulates polymorphonuclear leukocytes to produce an oxidative burst, lethal to the bacteria.
The ability of S. pneumoniae to repair the oxidative DNA damages in its genome, caused by this host defense contributes to this pathogen’s virulence. Consistent with this premise, Li et al. reported that, among different transformable S. pneumoniae isolates, nasal colonization fitness and virulence depend on an intact competence system. S. pneumoniae is part of the normal upper respiratory tract flora. As with many natural flora, it can become pathogenic under the right conditions when the immune system of the host is suppressed. Invasins, such as pneumolysin, an antiphagocytic capsule, various adhesins, immunogenic cell wall components are all major virulence factors. After S. pneumoniae colonizes the air sacs of the lungs, the body responds by stimulating the inflammatory response, causing plasma and white blood cells to fill the alveoli. This condition is called pneumonia, it is susceptible to clindamycin. Pneumonia is the most common of the S. pneumoniae diseases which include symptoms such as fever and chills, rapid breathing, difficulty breathing, chest pain.
For the elderly, they may include confusion, low alertness, the former listed symptoms to a lesser degree. Pneumococcal me
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
A pulmonary alveolus is a hollow cavity found in the lung parenchyma, is the basic unit of ventilation. Lung alveoli are the ends of the respiratory tree, branching from either alveolar sacs or alveolar ducts, which like alveoli are both sites of gas exchange with the blood as well. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates; the alveolar membrane is the gas exchange surface. Carbon dioxide rich blood is pumped from the rest of the body into the capillaries that surround the alveoli where, through diffusion, carbon dioxide is released and oxygen is absorbed; the alveoli are located in the respiratory zone of the lungs, at the ends of the alveolar ducts and alveolar sac, representing the smallest units in the respiratory tract. They provide total surface area of about 75m2. A typical pair of human lungs contain about 480 million alveoli; each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area. An adult alveolus has an average diameter of 200 µm, with an increase in diameter during inhalation.
The alveoli consist of an epithelial layer and an extracellular matrix surrounded by small blood vessels called capillaries. In some alveolar walls there are pores between alveoli called Pores of Kohn; the alveoli contain elastic fibers. The elastic fibres allow the alveoli to stretch, they spring back during exhalation in order to expel the carbon dioxide-rich air. There are three major types of cell in the alveolar wall: two types of alveolar cell and a large phagocyte known as an alveolar macrophage. Type I cells form the structure of the alveoli. Type I alveolar cells are squamous and cover 90–95% of the alveolar surface. Type I cells are involved in the process of gas exchange between blood; these cells are thin – the electron microscope was needed to prove that all alveoli are covered with an epithelial lining. These cells need to be so thin to be permeable for enabling an easy gas exchange between the alveoli and the blood. Organelles of type I alveolar cells such as the endoplasmic reticulum, Golgi apparatus and mitochondria are clustered around the nucleus.
The nuclei occupy large areas of free cytoplasm. This reduces the thickness of the cell; the cytoplasm in the thin portion contains pinocytotic vesicles which may play a role in the removal of small particulate contaminants from the outer surface. In addition to desmosomes, all type I alveolar cells have occluding junctions that prevent the leakage of tissue fluid into the alveolar air space. Type I pneumocytes are susceptible to toxic insults. In the event of damage, type II cells can proliferate and differentiate into type I cells to compensate. Type II cells secrete pulmonary surfactant to lower the surface tension of water and allows the membrane to separate, therefore increasing its capability to exchange gases; the surfactant is continuously released by exocytosis. It forms an underlying aqueous protein-containing hypophase and an overlying phospholipid film composed of dipalmitoyl phosphatidylcholine. Type II alveolar cells cover a small fraction of the alveolar surface area. Type II cells are capable of cellular division, giving rise to more type I and II alveolar cells when the lung tissue is damaged.
These cells are granular and cuboidal. Type II alveolar cells are found at the blood-air barrier. Although they only make up <5% of the alveolar surface, they are numerous. The alveolar macrophages called dust cells, destroy foreign materials and microbes such as bacteria. Type I cells are flat cells lining the alveolar walls; each alveolus is surrounded by numerous capillaries, is the site of gas exchange, which occurs by diffusion. The low solubility of oxygen necessitates the large internal surface area and thin walls of the alveoli. Weaving between the capillaries and helping to support them is an extracellular matrix, a meshlike fabric of elastic and collagenous fibres; the collagen fibres, being more rigid, give the wall firmness, while the elastic fibres permit expansion and contraction of the walls during breathing. Type II cells in the alveolar wall contain secretory granular organelles known as lamellar bodies that fuse with the cell membranes and secrete pulmonary surfactant; this surfactant is a film of fatty substances, a group of phospholipids that reduce alveolar surface tension.
The phospholipid are stored in the lamellar bodies. Without this coating, the alveoli would collapse and large forces would be required to re-expand them. Type II cells start to develop at about 26 weeks of gestation, secreting small amounts of surfactant. However, adequate amounts of surfactant are not secreted until about 35 weeks of gestation - this is the main reason for increased rates of infant respiratory distress syndrome, which drastically reduces at ages above 35 weeks gestation. Type II pneumocytes will replicate to replace damaged type I cells. MUC1, a human gene associated with type II pneumocytes, has been identified as a marker in lung cancer. Another type of cell, known as an alveolar macrophage, resides on the internal surfaces of the air cavities of the alveoli, the alveolar ducts, the bronchioles, they are mobile scavengers that serve to engulf
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
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 water, contains proteins, mineral ions, carbon dioxide, blood cells themselves. Albumin is the main protein in plasma, it functions to regulate the colloidal osmotic pressure of blood; the blood cells are red blood cells, white blood cells and platelets. The most abundant cells in vertebrate blood are red blood cells; these contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and increasing its solubility in blood. In contrast, carbon dioxide is 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, instead of hemoglobin. 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 tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune system, based on white blood cells. White blood cells help to resist 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. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.
Medical terms related to blood begin with hemo- or hemato- from the Greek word αἷμα for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen. Blood performs many important functions within the body, including: Supply of oxygen to tissues Supply of nutrients such as glucose, amino acids, fatty acids Removal of waste such as carbon dioxide and lactic acid Immunological functions, including circulation of white blood cells, detection of foreign material by antibodies Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding Messenger functions, including the transport of hormones and the signaling of tissue damage Regulation of core body temperature Hydraulic functions Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m3 close to pure water's density of 1000 kg/m3.
The average adult has a blood volume of 5 litres, composed of plasma and several kinds of cells. These blood cells consist of erythrocytes and thrombocytes. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, 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 blood's hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals; the red blood cells are marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit, is about 45%; the combined surface area of all red blood cells of the human body would be 2,000 times as great as the body's exterior surface.
4,000–11,000 leukocytes: White blood cells are part of the body's immune system. The cancer of leukocytes is called leukemia. 200,000 -- 500,000 thrombocytes: Also called platelets. Fibrin from the coagulation cascade creates a mesh over the platelet plug. About 55% of blood is blood plasma, a fluid, the blood's liquid medium, which by itself is straw-yellow in color; the blood plasma volume totals of 2.7–3.0 liters in an average human. It is an aqueous solution containing 92% water, 8% blood plasma proteins, trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose, amino acids, fatty acids, removes waste products, such as carbon dioxide and lactic acid. Other important components include: Serum albumin Blood-clotting factors Immunoglobulins lipoprotein particles Various