1.
Latin
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Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
2.
Anatomical terminology
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Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors. Anatomical terminology uses many terms, suffixes, and prefixes deriving from Ancient Greek. These terms can be confusing to those unfamiliar with them, but can be more precise reducing ambiguity, also, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted. By using precise anatomical terminology such ambiguity is eliminated, an international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the prefixes and suffixes are used to add meanings to different roots. The root of a term refers to an organ, tissue. For example, in the disorder hypertension, the prefix hyper- means high or over, the roots, prefixes and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants. Latin names of such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for two-headed. The first word tells us what we are speaking about, the second describes it, when describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, the cephalon or cephalic region refers to the head. This area is differentiated into the cranium, facies, frons, oculus, auris, bucca, nausus, oris. The neck area is called the cervicis or cervical region, examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body, for example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, similarly, in the arms, different terminology is often used in the arms, in part to reduce ambiguity as what is the front, back, inner and outer surfaces. For this reason, the terms below are used, Radial referring to the radius bone, ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet. International morphological terminology is used by the colleges of medicine and dentistry and it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research, teaching and medical care. The international morphological terminology refers to morphological sciences as a biological sciences branch, in this field, the form and structure are examined as well as the changes or developments in the organism
3.
Hormone
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Hormones have diverse chemical structures, mainly of 3 classes, eicosanoids, steroids, and amino acid/protein derivatives. The glands that secrete hormones comprise the endocrine signaling system, the term hormone is sometimes extended to include chemicals produced by cells that affect the same cell or nearby cells. Hormones affect distant cells by binding to receptor proteins in the target cell resulting in a change in cell function. When a hormone binds to the receptor, it results in the activation of a signal transduction pathway, Hormone secretion may occur in many tissues. Endocrine glands are the example, but specialized cells in various other organs also secrete hormones. Hormone secretion occurs in response to specific biochemical signals from a range of regulatory systems. Upon secretion, certain hormones, including hormones and catecholamines, are water-soluble and are thus readily transported through the circulatory system. The endocrine system secretes hormones directly into the bloodstream typically into fenestrated capillaries, Hormones with paracrine function diffuse through the interstitial spaces to nearby target tissue. The reaction of the cells may then be recognized by the original hormone-producing cells. This is an example of a negative feedback loop. Hormone cells are typically of a cell type, residing within a particular endocrine gland, such as the thyroid gland, ovaries. Hormones exit their cell of origin via exocytosis or another means of membrane transport, the hierarchical model is an oversimplification of the hormonal signaling process. Different tissue types may also respond differently to the same hormonal signal, the rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors that influence the metabolism and excretion of hormones, thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an effect of the hormone, for example, thyroid-stimulating hormone causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones. To release active hormones quickly into the circulation, hormone biosynthetic cells may produce and these can then be quickly converted into their active hormone form in response to a particular stimulus. Eicosanoids are considered to act as local hormones and they are considered to be local because they possess specific effects on target cells close to their site of formation. They also have a rapid degradation cycle, making sure they do not reach distal sites within the body, most hormones initiate a cellular response by initially binding to either cell membrane associated or intracellular receptors
4.
Gland
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A gland is an organ in an animals body that synthesizes substances for release into the bloodstream or into cavities inside the body or its outer surface. Every gland is formed by an ingrowth from an epithelial surface and this ingrowth may in the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated. As growth proceeds, the column of cells may divide or give off offshoots, in many glands, the number of branches is limited, in others a very large structure is finally formed by repeated growth and sub-division. As a rule, the branches do not unite with one another, but in one instance, the liver, glands are classified according to their shape. If the gland retains its shape as a tube throughout it is termed a tubular gland, in the second main variety of gland the secretory portion is enlarged and the lumen variously increased in size. These are termed alveolar or saccular glands, glands are divided based on their function into two groups, Endocrine glands secrete substances that circulate through the blood stream. These glands that secrete their products through the basal lamina into the blood stream and these glands often secrete hormones, and play an important role in maintaining homeostasis. The pineal gland, thymus gland, pituitary gland, thyroid gland, exocrine glands secrete their products through a duct onto an outer surface of the body, such as the skin or the gastrointestinal tract. Secretion is directly onto the apical surface, the glands in this group can be divided into three groups, Apocrine glands a portion of the secreting cells body is lost during secretion. E. g. mammary gland, sweat gland of arm pit, pubic region, skin around anus, lips, holocrine glands the entire cell disintegrates to secrete its substances, meibomian and zeis glands. Merocrine glands cells secrete their substances by exocytosis, E. g. max sweat gland of humans, goblet cells, salivary gland, tear gland, intestinal glands. The type of product of exocrine glands may also be one of three categories, Serous glands secrete a watery, often protein-rich, fluid-like product, e. g. sweat glands. Mucous glands secrete a viscous product, rich in carbohydrates, e. g. goblet cells, sebaceous glands secrete a lipid product. These glands are known as oil glands, e. g. Fordyce spots. Adenosis is any disease of a gland, the diseased gland has abnormal formation or development of glandular tissue which is sometimes tumorous. This article incorporates text from a now in the public domain, Chisholm, Hugh
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Organism
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In biology, an organism is any contiguous living system, such as an animal, plant, fungus, protist, archaeon, or bacterium. All known types of organisms are capable of some degree of response to stimuli, reproduction, growth and development and homeostasis. An organism consists of one or more cells, when it has one cell it is known as an organism. Most unicellular organisms are of microscopic scale and are thus described as microorganisms. Humans are multicellular organisms composed of trillions of cells grouped into specialized tissues. An organism may be either a prokaryote or a eukaryote, prokaryotes are represented by two separate domains—bacteria and archaea. Eukaryotic organisms are characterized by the presence of a cell nucleus. Fungi, animals and plants are examples of kingdoms of organisms within the eukaryotes, estimates on the number of Earths current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to five billion species. In 2016, a set of 355 genes from the last universal ancestor of all living organisms living was identified. The term organism first appeared in the English language in 1703 and it is directly related to the term organization. There is a tradition of defining organisms as self-organizing beings. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using such as any living structure, such as a plant, animal, fungus or bacterium, capable of growth. Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the machinery of a host cell for reproduction. A superorganism is an organism consisting of individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism, several contributions are responses to the suggestion that the category of organism may well not be adequate in biology. Viruses are not typically considered to be organisms because they are incapable of autonomous reproduction and this controversy is problematic because some cellular organisms are also incapable of independent survival and live as obligatory intracellular parasites
6.
Homeostasis
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Each of these variables is controlled by a separate “homeostat”, which, together, maintain life. The concept was described by French physiologist Claude Bernard in 1865, the term cybernetics is applied to technological control systems such as thermostats, which function as homeostats, but is often defined much more broadly than the biological term homeostasis. The word homeostasis uses combining forms of homeo- and -stasis, New Latin from Greek, ὅμοιος homoios, similar and στάσις stasis, standing still, yielding the idea of staying the same. The conceptual origins of homeostasis reach back to the ancient Greek concepts of balance, harmony, equilibrium, following these hypotheses, Hippocrates compared health to the harmonious balance of the elements, and illness and disease to the systematic disharmony of these elements. Cannon published an extrapolation from Bernards 1865 work naming his theory homeostasis, Cannon further posited that threats to homeostasis might originate from the external environment or the internal environment, and could be physical or psychological, as in emotional distress. Cannon identified these negative feedback systems and emphasized that, regardless of the nature of the threat to homeostasis, the metabolic processes of all living organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the bathing the cells in multicellular creatures. However, a great many other homeostats, encompassing many aspects of human physiology, if an entity is homeostatically controlled it does not imply that its value is necessarily absolutely steady in health. Core body temperature is, for instance, regulated by a homeostat with temperature sensors in, amongst others, however the set point of the regulator is regularly reset. For instance, core temperature in humans varies during the course of the day, with the lowest temperatures occurring at night. The temperature regulators set point is readjusted in adult women at the start of the phase of the menstrual cycle. The temperature regulators set point is reset during infections to produce a fever, Homeostasis does not govern every activity in the body. For instance the signal from the sensor to the effector is, of necessity, highly variable in order to information about the direction. Similarly the effector’s response needs to be adjustable to reverse the error – in fact it should be very nearly in proportion to the error that is threatening the internal environment. The sensors send messages via sensory nerves to the medulla oblongata of the brain indicating whether the pressure has fallen or risen. One of the effector organs is the heart rate is stimulated to rise when the arterial blood pressure falls. Thus the heart rate is not homeostatically controlled, but is one of effector responses to errors in the blood pressure. Another example is the rate of sweating, the blood urea concentration is an example
7.
Human
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Modern humans are the only extant members of Hominina tribe, a branch of the tribe Hominini belonging to the family of great apes. Several of these hominins used fire, occupied much of Eurasia and they began to exhibit evidence of behavioral modernity around 50,000 years ago. In several waves of migration, anatomically modern humans ventured out of Africa, the spread of humans and their large and increasing population has had a profound impact on large areas of the environment and millions of native species worldwide. Humans are uniquely adept at utilizing systems of communication for self-expression and the exchange of ideas. Humans create complex structures composed of many cooperating and competing groups, from families. Social interactions between humans have established a wide variety of values, social norms, and rituals. These human societies subsequently expanded in size, establishing various forms of government, religion, today the global human population is estimated by the United Nations to be near 7.5 billion. In common usage, the word generally refers to the only extant species of the genus Homo—anatomically and behaviorally modern Homo sapiens. In scientific terms, the meanings of hominid and hominin have changed during the recent decades with advances in the discovery, there is also a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species. The English adjective human is a Middle English loanword from Old French humain, ultimately from Latin hūmānus, the words use as a noun dates to the 16th century. The native English term man can refer to the species generally, the species binomial Homo sapiens was coined by Carl Linnaeus in his 18th century work Systema Naturae. The generic name Homo is a learned 18th century derivation from Latin homō man, the species-name sapiens means wise or sapient. Note that the Latin word homo refers to humans of either gender, the genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids branch of the primates. The closest living relatives of humans are chimpanzees and gorillas, with the sequencing of both the human and chimpanzee genome, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%. The gibbons and orangutans were the first groups to split from the leading to the humans. The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch, during this split, chromosome 2 was formed from two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. There is little evidence for the divergence of the gorilla, chimpanzee. Each of these species has been argued to be an ancestor of later hominins
8.
Endocrine gland
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Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The major glands of the system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus. The hypothalamus and pituitary gland are neuroendocrine organs, the ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormone can bind. Changes in number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones, blood levels of hormones reflect a balance between secretion and degradation/excretion. The liver and kidneys are the organs that degrade hormones, breakdown products are excreted in urine. Hormone half-life and duration of activity are limited and vary from hormone to hormone, permissiveness is the situation in which a hormone cannot exert its full effects without the presence of another hormone. Synergism occurs when two or more hormones produce the effects in a target cell and their results are amplified. Antagonism occurs when a hormone opposes or reverses the effect of another hormone, the endocrine glands belong to the bodys control system. The hormones which they help to regulate the functions of cells. Endocrine organs are activated to release their hormones by humoral, neural or hormonal stimuli, negative feedback is important in regulating hormone levels in the blood. The nervous system, acting through hypothalamic controls, can in certain cases override or modulate hormonal effects, the pituitary gland hangs from the base of the brain by a stalk and is enclosed by bone. It consists of a glandular portion and a neural portion. The hypothalamus regulates the output of the anterior pituitary and synthesizes two hormones that it exports to the posterior pituitary for storage and later release. Four of the six anterior pituitary hormones are tropic hormones that regulate the function of other endocrine organs, most anterior pituitary hormones exhibit a diurnal rhythm of release, which is subject to modification by stimuli influencing the hypothalamus. Somatotropic hormone or Growth hormone is a hormone that stimulates growth of all body tissues but especially skeletal muscle. It may act directly, or indirectly via insulin-like growth factors, GH mobilizes fats, stimulates protein synthesis, and inhibits glucose uptake and metabolism. Secretion is regulated by growth hormone releasing hormone and growth hormone inhibiting hormone, hypersecretion causes gigantism in children and acromegaly in adults, hyposecretion in children causes pituitary dwarfism. Thyroid-stimulating hormone promotes normal development and activity of the thyroid gland, thyrotropin-releasing hormone stimulates its release, negative feedback of thyroid hormone inhibits it
9.
Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
10.
Endocrinology
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Endocrinology is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. Specializations include behavioral endocrinology and comparative endocrinology, the endocrine system consists of several glands, all in different parts of the body, that secrete hormones directly into the blood rather than into a duct system. Endocrinology is the study of the system in the human body. This is a system of glands which secrete hormones, hormones are chemicals which affect the actions of different organ systems in the body. Examples include thyroid hormone, growth hormone, and insulin, the endocrine system involves a number of feedback mechanisms, so that often one hormone will control the action or release of another secondary hormone. If there is too much of the hormone, it may provide negative feedback to the primary hormone. This definition holds for most classical hormones, but there are also paracrine mechanisms, autocrine signals, a neuroendocrine signal is a classical hormone that is released into the blood by a neurosecretory neuron. Peptide hormones and protein hormones consist of three to more than 200 amino acid residues and can have a mass as large as 30,000 grams per mole. All hormones secreted by the pituitary gland are peptide hormones, as are leptin from adipocytes, ghrelin from the stomach, steroid hormones are converted from their parent compound, cholesterol. Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind, glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens. Some forms of vitamin D, such as calcitriol, are steroid-like and bind to homologous receptors and these organs include the pituitary, thyroid, adrenals, ovaries, testes, and pancreas. An endocrinologist is a physician who specializes in treating disorders of the system, such as diabetes, hyperthyroidism. The diagnosis and treatment of diseases are guided by laboratory tests to a greater extent than for most specialties. Many diseases are investigated through excitation/stimulation or inhibition/suppression testing and this might involve injection with a stimulating agent to test the function of an endocrine organ. Blood is then sampled to assess the changes of the relevant hormones or metabolites, an endocrinologist needs extensive knowledge of clinical chemistry and biochemistry to understand the uses and limitations of the investigations. A second important aspect of the practice of endocrinology is distinguishing human variation from disease, atypical patterns of physical development and abnormal test results must be assessed as indicative of disease or not. Diagnostic imaging of endocrine organs may reveal incidental findings called incidentalomas, Endocrinology involves caring for the person as well as the disease. Most endocrine disorders are diseases that need lifelong care
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Exocrine gland
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Exocrine glands are glands that produce and secrete substances onto an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, exocrine glands are one of two types of glands in the human body, the other being endocrine glands, which secrete their products directly into the bloodstream. Exocrine glands contain a portion and a duct portion, the structures of which can be used to classify the gland. The duct portion may be branched or unbranched, the glandular portion may be tubular or acinar, or may be a mix of the two. If the glandular portion branches, then the gland is called a branched gland, exocrine glands are named apocrine glands, holocrine glands, or merocrine glands based on how their products are excreted. Merocrine secretion – cells excrete their substances by exocytosis, for example, apocrine secretion – a portion of the cell membrane that contains the excretion buds off. Holocrine secretion – the entire cell disintegrates to excrete its substance, for example, sebaceous glands of the skin, serous cells excrete proteins, often enzymes. Examples include gastric chief cells and Paneth cells Mucous cells excrete mucus, examples include Brunners glands, esophageal glands, and pyloric glands Mixed glands excrete both protein and mucus. List of glands of the human body List of specialized glands within the human integumentary system Diagram at mhhe. com
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Salivary gland
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In humans and some other mammals the secretion is alpha-amylase also known as ptyalin. The salivary glands are detailed below, The two parotid glands are major salivary glands wrapped around the mandibular ramus in humans, the largest of the salivary glands, they secrete saliva to facilitate mastication and swallowing, and amylase to begin the digestion of starches. It is the type of gland which secretes the ptyalin. It enters the cavity via the parotid duct or Stensen duct. The glands are located posterior to the mandibular ramus and anterior to the process of the temporal bone. They produce 20% of the total salivary content in the oral cavity, the submandibular glands are a pair of major salivary glands located beneath the lower jaws, superior to the digastric muscles. The secretion produced is a mixture of both fluid and mucus, and enters the oral cavity via the submandibular duct or Wharton duct. It is located two fingers above the Adams apple and about two inches apart under the chin. The sublingual glands are a pair of salivary glands located inferior to the tongue. The secretion produced is mainly mucous in nature, however, it is categorized as a mixed gland, approximately 5% of saliva entering the oral cavity comes from these glands. They are 1-2mm in diameter and unlike the major glands, they are not encapsulated by connective tissue, the gland has usually a number of acini connected in a tiny lobule. A minor salivary gland may have a common excretory duct with another gland and their secretion is mainly mucous in nature and have many functions such as coating the oral cavity with saliva. Problems with dentures are sometimes associated with salivary glands if there is dry mouth present. The minor salivary glands are innervated by the seventh cranial or facial nerve, von Ebners glands are glands found in a trough circling the circumvallate papillae on the dorsal surface of the tongue near the terminal sulcus. They secrete a purely serous fluid that begins lipid hydrolysis and they also facilitate the perception of taste through secretion of digestive enzymes and proteins. The arrangement of these glands around the circumvallate papillae provides a flow of fluid over great number of taste bud along the sides of the papillae. It is important for dissolving the food particles to be tested, Salivary glands are innervated, either directly or indirectly, by the parasympathetic and sympathetic arms of the autonomic nervous system. Parasympathetic stimulation evokes a copious flow of saliva, in contrast, sympathetic stimulation produces either a small flow, which is rich in protein, or no flow at all
13.
Gastrointestinal tract
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Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. A tract is a collection of related anatomic structures or a series of connected body organs, the mouth, oesophagus, stomach, and intestines are part of the human alimentary canal. All bilaterians have a gastrointestinal tract, also called a gut or an alimentary canal and this is a tube that transfers food to the organs of digestion. In large bilaterians, the gastrointestinal tract generally also has an exit, some small bilaterians have no anus and dispose of solid wastes by other means. The gastrointestinal tract contains thousands of different bacteria in their gut flora, the human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. In contrast, the digestive system comprises the gastrointestinal tract plus the accessory organs of digestion. The tract may also be divided into foregut, midgut, and hindgut, the whole human GI tract is about nine metres long at autopsy. The GI tract releases hormones from enzymes to help regulate the digestive process, the structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, the upper gastrointestinal tract consists of the buccal cavity, pharynx, esophagus, stomach, and duodenum. The exact demarcation between the upper and lower tracts is the muscle of the duodenum. Upon dissection, the duodenum may appear to be an organ, but it is divided into four segments based upon function, location. The four segments of the duodenum are as follows, bulb, descending, horizontal, the suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm. The suspensory muscle is an important anatomical landmark which shows the division between the duodenum and the jejunum, the first and second parts of the small intestine. This is a muscle which is derived from the embryonic mesoderm. The lower gastrointestinal tract includes most of the intestine and all of the large intestine. In humans, the intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the cecum, colon, rectum. The small intestine begins at the duodenum, which receives food from the stomach and it is a tubular structure, usually between 6 and 7 m long. The area of the human, adult small intestinal mucosa is about 30 m2 and its main function is to absorb the products of digestion into the bloodstream
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Erythropoietin
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Erythropoietin, also known as EPO, hematopoietin, or hemopoietin, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production. It is a cytokine for erythrocyte precursors in the bone marrow, human EPO has a molecular weight of 34 kDa. Erythropoietin is produced by fibroblasts in the kidney in close association with peritubular capillary. It is also produced in cells in the liver. While liver production predominates in the fetal and perinatal period, renal production is predominant during adulthood, exogenous erythropoietin can be provided to people whose kidneys cannot make enough. Recombinant human erythropoietin is produced by recombinant DNA technology in cell culture, several different pharmaceutical agents are available with a variety of glycosylation patterns and are collectively called erythropoiesis-stimulating agents. Major examples are epoetin alfa and epoetin beta, boxed warnings include a risk of death, myocardial infarction, stroke, venous thromboembolism, and tumor recurrence. Erythropoietin is an essential hormone for red blood cell production, without it, definitive erythropoiesis does not take place. Erythropoietin has its effect on red blood cell progenitors and precursors by promoting their survival through protecting these cells from apoptosis. Erythropoietin is the primary factor that cooperates with various other growth factors involved in the development of erythroid lineage from multipotent progenitors. The burst-forming unit-erythroid cells start erythropoietin receptor expression and are sensitive to erythropoietin, subsequent stage, the colony-forming unit-erythroid, expresses maximal erythropoietin receptor density and is completely dependent on erythropoietin for further differentiation. Precursors of red cells, the proerythroblasts and basophilic erythroblasts also express erythropoietin receptor and are affected by it. However this proposal is controversial with numerous studies showing no effect and it is also inconsistent with the low levels of Epo receptors on those cells. Clinical trials in humans with ischemic heart, neural and renal tissues have not demonstrated the same seen in animals. Erythropoietin has been shown to exert its effects by binding to the erythropoietin receptor, EPO is highly glycosylated, with half-life in blood around five hours. EPOs half-life may vary between endogenous and various recombinant versions, additional glycosylation or other alterations of EPO via recombinant technology have led to the increase of EPOs stability in blood. EPO binds to the receptor on the red cell progenitor surface. This initiates the STAT5, PIK3 and Ras MAPK pathways and this results in differentiation, survival and proliferation of the erythroid cell
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Renin
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Thus, it regulates the bodys mean arterial blood pressure. Renin can be referred to as a hormone even though it has no peripheral receptors, the primary structure of renin precursor consists of 406 amino acids with a pre- and a pro-segment carrying 20 and 46 amino acids, respectively. Mature renin contains 340 amino acids and has a mass of 37 kDa and this is the most direct causal link between blood pressure and renin secretion. A decrease in sodium load delivered to the distal tubule and this load is measured by the macula densa of the juxtaglomerular apparatus. Sympathetic nervous system activity, which controls blood pressure, acting through the beta1 adrenergic receptors. Human renin is secreted by at least 2 cellular pathways, a pathway for the secretion of the precursor prorenin. The renin enzyme circulates in the stream and breaks down angiotensinogen secreted from the liver into the peptide angiotensin I. Angiotensin I is further cleaved in the lungs by endothelial-bound angiotensin-converting enzyme into angiotensin II, angiotensin II is a potent constrictor of all blood vessels. It acts on the muscle and, therefore, raises the resistance posed by these arteries to the heart. The heart, trying to overcome this increase in its load, works more vigorously, the normal concentration of renin in adult human plasma is 1. 98–24.6 ng/L in the upright position. Renins primary function is therefore to eventually cause an increase in blood pressure, renin is secreted from juxtaglomerular kidney cells, which sense changes in renal perfusion pressure, via stretch receptors in the vascular walls. The juxtaglomerular cells are stimulated to release renin by signaling from the macula densa. The macula densa senses changes in delivery to the distal tubule. Together, the macula densa and juxtaglomerular cells comprise the juxtaglomerular complex, renin secretion is also stimulated by sympathetic nervous stimulation, mainly through beta-1 adrenoceptor activation. Renin can bind to ATP6AP2, which results in an increase in the conversion of angiotensinogen to angiotensin I over that shown by soluble renin. In addition, renin binding results in phosphorylation of serine and tyrosine residues of ATP6AP2, the level of renin mRNA appears to be modulated by the binding of HADHB, HuR and CP1 to a regulatory region in the 3 UTR. The gene for renin, REN, spans 12 kb of DNA and it produces several mRNA that encode different REN isoforms. Mutations in the REN gene can be inherited, and are a cause of a rare inherited kidney disease, many—but not all—patients and families with this disease suffer from an elevation in serum potassium and unexplained anemia relatively early in life
16.
Steroid
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A steroid is an organic compound with four rings arranged in a specific configuration. Examples include the dietary lipid cholesterol, the sex hormones estradiol and testosterone, the steroid core structure is composed of seventeen carbon atoms, bonded in four fused rings, three six-member cyclohexane rings and one five-member cyclopentane ring. Steroids vary by the groups attached to this four-ring core. Sterols are forms of steroids with a group at position three and a skeleton derived from cholestane. They can also vary more markedly by changes to the ring structure, hundreds of steroids are found in plants, animals and fungi. All steroids are manufactured in cells from the sterols lanosterol or cycloartenol, lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene. The three cyclohexane rings form the skeleton of a derivative of phenanthrene. The D ring has a cyclopentane structure, when the two methyl groups and eight carbon side chains are present, the steroid is said to have a cholestane framework. The following are some categories of steroids. In eukaryotes, steroids are found in fungi, animals, animal steroids include compounds of vertebrate and insect origin, the latter including ecdysteroids such as ecdysterone. Steroid hormones include, Sex hormones, which influence sex differences and these include androgens, estrogens, and progestagens. In popular use, the term often refers to anabolic steroids. Plant steroids include steroidal alkaloids found in Solanaceae, the phytosterols, in prokaryotes, biosynthetic pathways exist for the tetracyclic steroid framework – where its origin from eukaryotes is conjectured – and the more-common pentacyclic triterpinoid hopanoid framework. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog, examples of this classification include, The gonane is the parent 17-carbon tetracyclic hydrocarbon molecule with no alkyl sidechains. Secosteroids are a subclass of steroidal compounds resulting, biosynthetically or conceptually, major secosteroid subclasses are defined by the steroid carbon atoms where this scission has taken place. Norsteroids and homosteroids are structural subclasses of steroids formed from biosynthetic steps, the former involves enzymic ring expansion-contraction reactions, and the latter is accomplished or through ring closures of acyclic precursors with more ring atoms than the parent steroid framework. Combinations of these alterations are known in nature. Ingestion of these C-nor-D-homosteroids results in defects in lambs, cyclopia from cyclopamine
17.
Eicosanoid
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In performing these tasks, eicosanoids most often act as autocrine signaling agents to impact their cells of origin or as paracrine signaling agents to impact cells near to their cells of origin. However, they can act as endocrine agents to control the function of distant cells. Mammals, including humans, are unable to convert ω-6 into ω-3 PUFA, in consequence, tissue levels of the ω-6 and ω-3 PUFAs and their corresponding eicosanoid metabolites link directly to the amount of dietary ω-6 versus ω-3 PUFAs consumed. Eicosanoid is the term for straight-chain polyunsaturated fatty acids of 20 carbon units in length that have been metabolized or otherwise converted to oxygen-containing products. Adrenic acid,7,10,13, 16-docosatetraenoic acid, is an ω-6 fatty acid with four cis double bounds, each located between carbons 7-8, 10-11, 13-14, and 17-18. 5Z, 8Z, 11Z, 14Z, 17Z-eicosapentaenoic acid is an ω-3 fatty acid with five cis double bonds, each located between carbons 5-8, 8-9,11, -12, 14-15, and 17-18. Dihomo-gamma-linolenic acid, 8Z, 11Z, 14Z-eicosatrienoic acid is an ω-6 fatty acid with three cis double bonds, each located between carbons 8-9,11, -12, and 14-15. Mead acid, i. e. 5Z, 8Z, 11Z-eicosatrienoic acid, is an ω-9 fatty acid containing three cis double bonds, each located between carbons 5-6, 8-9, and 11, -12. Examples are, The EPA-derived prostanoids have three double bonds while leukotrienes derived from EPA have five double bonds, the AA-derived prostanoids have two double bonds while their AA-derived leukotrienes have four double bonds. Hydroperoxy-, hydroxyl-, and oxo-eicosanoids possess a hydroperoxy, hydroxy and their trivial names indicate the substituent as, Hp or HP for a hydroperoxy residue, H for a hydroxy residue, and oxo- for an oxo residue. g. ALOX12B forms R chirality products, i. e. 12R-HpETE and 12R-HETE, similarly, ALOXE3 metabolizes arachidonic acid to 12R-HpETE and 12R-HETE, however these are minor products that this enzyme forms only under a limited set of conditions. ALOXE3 preferentially metabolizes arachidonic acid to hepoxilins, all of these epoxides are converted, sometimes rapidly, to their dihydroxy metabolites, by various cells and tissues. PGH2 has a 5-carbon ring bridged by molecular oxygen, the 5-carbon ring of prostacyclin is conjoined to a second ring consisting of 4 carbon and one oxygen atom. See Leukotriene#Biosynthesis, Hydroxyeicosatetraenoic acid, and Eoxin#Human biosynthesis, alternately, ALOX5 uses its LTA synthase activity to act convert 5-HPETE to leukotriene A4. LTA4 is then metabolized either to LTB4 by Leukotriene A4 hydrolase or Leukotriene C4 by either LTC4 synthase or microsomal glutathione S-transferase 2, either of the latter two enzymes act to attach the sulfur of cysteines thio- group in the tripeptide glutamate-cysteine-glycine to carbon 6 of LTA4 thereby forming LTC4. After release from its parent cell, the glutamate and glycine residues of LTC4 are removed step-wise by gamma-glutamyltransferase, the decision to form LTB4 versus LTC4 depends on the relative content of LTA4 hydrolase versus LTC4 synthase class of eicosanoids, possess anti-inflammatory and inflammation resolving activity. RvE1 is also in development studies for the treatment of neurodegenerative diseases. They are proposed to reduce the actions of their aracidonate-derived analogs by replacing their production with weaker analogs, eicosapentaenoic acid-derived counterparts of the Eoxins have not been described
18.
Leukotriene
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Leukotrienes use lipid signaling to convey information to either the cell producing them or neighboring cells in order to regulate immune responses. Leukotriene production is accompanied by the production of histamine and prostaglandins. One of their roles is to trigger contractions in the smooth muscles lining the bronchioles, their overproduction is a cause of inflammation in asthma. Leukotriene antagonists are used to treat these disorders by inhibiting the production or activity of leukotrienes, the name leukotriene, introduced by Swedish biochemist Bengt Samuelsson in 1979, comes from the words leukocyte and triene. What would be later named leukotriene C, slow reaction smooth muscle-stimulating substance was originally described between 1938 and 1940 by Feldberg and Kellaway, the researchers isolated SRS from lung tissue after a prolonged period following exposure to snake venom and histamine. Leukotrienes are commercially available to the research community, LTC4, LTD4, LTE4 and LTF4 are often called cysteinyl leukotrienes due to the presence of the amino acid cysteine in their structure. The cysteinyl leukotrienes make up the substance of anaphylaxis. LTF4, like LTD4, is a metabolite of LTC4, but, unlike LTD4, LTB4 is synthesized in vivo from LTA4 by the enzyme LTA4 hydrolase. Its primary function is to recruit neutrophils to areas of tissue damage, drugs that block the actions of LTB4 have shown some efficacy in slowing the progression of neutrophil-mediated diseases. There has also postulated the existence of LTG4, a metabolite of LTE4 in which the cysteinyl moiety has been oxidized to an alpha-keto-acid. Very little is known about this putative leukotriene, leukotrienes originating from the omega-3 class eicosapentanoic acid have diminished inflammatory effects. Leukotrienes are synthesized in the cell from arachidonic acid by arachidonate 5-lipoxygenase, the catalytic mechanism involves the insertion of an oxygen moiety at a specific position in the arachidonic acid backbone. The lipoxygenase pathway is active in leukocytes and other immunocompetent cells, including mast cells, eosinophils, neutrophils, monocytes, when such cells are activated, arachidonic acid is liberated from cell membrane phospholipids by phospholipase A2, and donated by the 5-lipoxygenase-activating protein to 5-lipoxygenase. 5-Lipoxygenase uses FLAP to convert arachidonic acid into 5-hydroperoxyeicosatetraenoic acid, which reduces to 5-hydroxyeicosatetraenoic acid. The enzyme 5-LO acts again on 5-HETE to convert it into leukotriene A4, in cells that express LTC4 synthase, such as mast cells and eosinophils, LTA4 is conjugated with the tripeptide glutathione to form the first of the cysteinyl-leukotrienes, LTC4. Outside the cell, LTC4 can be converted by enzymes to form successively LTD4 and LTE4. Both LTB4 and the cysteinyl-leukotrienes are partly degraded in local tissues, leukotrienes act principally on a subfamily of G protein-coupled receptors. They may also act upon peroxisome proliferator-activated receptors, leukotrienes are involved in asthmatic and allergic reactions and act to sustain inflammatory reactions
19.
Prostaglandin
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The prostaglandins are a group of physiologically active lipid compounds having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals and they are derived enzymatically from fatty acids. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring and they are a subclass of eicosanoids and of the prostanoid class of fatty acid derivatives. The structural differences between prostaglandins account for their different biological activities, a given prostaglandin may have different and even opposite effects in different tissues in some cases. The ability of the same prostaglandin to stimulate a reaction in one tissue and they act as autocrine or paracrine factors with their target cells present in the immediate vicinity of the site of their secretion. Prostaglandins differ from endocrine hormones in that they are not produced at a specific site, prostaglandins are powerful locally acting vasodilators and inhibit the aggregation of blood platelets. Through their role in vasodilation, prostaglandins are also involved in inflammation and they are synthesized in the walls of blood vessels and serve the physiological function of preventing needless clot formation, as well as regulating the contraction of smooth muscle tissue. Conversely, thromboxanes are vasoconstrictors and facilitate platelet aggregation and their name comes from their role in clot formation. Specific prostaglandins are named with a letter followed by a number, for example, prostaglandin E1 is abbreviated PGE1 or PGE1, and prostaglandin I2 is abbreviated PGI2 or PGI2. The name prostaglandin derives from the prostate gland, when prostaglandin was first isolated from seminal fluid in 1935 by the Swedish physiologist Ulf von Euler, and independently by M. W. Goldblatt, it was believed to be part of the prostatic secretions, in fact, prostaglandins are produced by the seminal vesicles. It was later shown that many other tissues secrete prostaglandins for various functions, the first total syntheses of prostaglandin F2α and prostaglandin E2 were reported by E. J. Corey in 1969, an achievement for which he was awarded the Japan Prize in 1989. In 1971, it was determined that aspirin-like drugs could inhibit the synthesis of prostaglandins, the biochemists Sune K. Bergström, Bengt I. Samuelsson and John R. Vane jointly received the 1982 Nobel Prize in Physiology or Medicine for their research on prostaglandins, prostaglandins are found in most tissues and organs. They are produced by almost all nucleated cells and they are autocrine and paracrine lipid mediators that act upon platelets, endothelium, uterine and mast cells. They are synthesized in the cell from the fatty acids. An intermediate arachidonic acid is created from diacylglycerol via phospholipase-A2, then brought to either the cyclooxygenase pathway or the lipoxygenase pathway, prostaglandins were originally believed to leave the cells via passive diffusion because of their high lipophilicity. The release of prostaglandin has now also shown to be mediated by a specific transporter, namely the multidrug resistance protein 4
20.
Paracrine signalling
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Paracrine signaling is a form of cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behavior of those cells. Signaling molecules known as paracrine factors diffuse over a short distance, as opposed to endocrine factors, juxtacrine interactions. Cells that produce paracrine factors secrete them into the extracellular environment. Factors then travel to nearby cells in which the gradient of factor received determines the outcome, however, the exact distance that paracrine factors can travel is not certain. Although paracrine signaling elicits a diverse array of responses in the cells, most paracrine factors utilize a relatively streamlined set of receptors. In fact, different organs in the body -even between different species - are known to utilize a sets of paracrine factors in differential development. The highly conserved receptors and pathways can be organized into four major families based on structures, Fibroblast growth factor family, Hedgehog family, Wnt family. Binding of a factor to its respective receptor initiates signal transduction cascades. Additionally, the cell must also have the ability to be mechanistically induced. Although the FGF family of paracrine factors has a range of functions. To fulfill many diverse functions, FGFs can be spliced or even have different initiation codons to create hundred of different FGF isoforms. One of the most important functions of the FGF receptors is in limb development and this signaling involves nine different alternatively spliced isoforms of the receptor. Fgf8 and Fgf10 are two of the players in limb development. In the forelimb initiation and limb growth in mice, axial cues from the intermediate mesoderm produces Tbx5, Fgf10 then signals to the ectoderm to begin production of Fgf8, which also stimulates the production of Fgf10. Deletion of Fgf10 results in limbless mice, additionally, paracrine signaling of Fgf is essential in the developing eye of chicks. The fgf8 mRNA becomes localized in what differentiates into the retina of the optic cup. These cells are in contact with the ectoderm cells, which will eventually become the lens. Phenotype and survival of mice after knockout of some FGFR genes, Paracrine signaling through fibroblast growth factors and this signaling pathway has been highly studied, using Drosophila eyes and human cancers
21.
New Latin
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New Latin was a revival in the use of Latin in original, scholarly, and scientific works between c.1375 and c. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy and international scientific vocabulary, in such use, New Latin is often viewed as still existing and subject to new word formation. As a language for full expression in prose or poetry, however, classicists use the term Neo-Latin to describe the Latin that developed in Renaissance Italy as a result of renewed interest in classical civilization in the 14th and 15th centuries. Neo-Latin also describes the use of the Latin language for any purpose, scientific or literary, during, the term New Latin came into widespread use towards the end of the 1890s among linguists and scientists. New Latin was, at least in its days, an international language used throughout Catholic and Protestant Europe. Russias acquisition of Kiev in the later 17th century introduced the study of Latin to Russia, though Latin and New Latin are considered extinct, large parts of their vocabulary have seeped into English and several Germanic languages. New Latin was inaugurated by the triumph of the humanist reform of Latin education, led by writers as Erasmus, More. Medieval Latin had been the working language of the Roman Catholic Church, taught throughout Europe to aspiring clerics. It was a language, full of neologisms and often composed without reference to the grammar or style of classical authors. Attempts at reforming Latin use occurred sporadically throughout the period, becoming most successful in the mid-to-late 19th century, the Protestant Reformation, though it removed Latin from the liturgies of the churches of Northern Europe, may have advanced the cause of the new secular Latin. Classic works such as Newtons Principia Mathematica were written in the language, throughout this period, Latin was a universal school subject, and indeed, the pre-eminent subject for elementary education in most of Europe and other places of the world that shared its culture. All universities required Latin proficiency to obtain admittance as a student, Latin was an official language of Poland—recognised and widely used between the 9th and 18th centuries, commonly used in foreign relations and popular as a second language among some of the nobility. As an auxiliary language to the local vernaculars, New Latin appeared in a variety of documents, ecclesiastical, legal, diplomatic, academic. As late as the 1720s, Latin was still used conversationally, for instance, the Hanoverian king George I of Great Britain, who had no command of spoken English, communicated in Latin with his Prime Minister Robert Walpole, who knew neither German nor French. By about 1700, the movement for the use of national languages had reached academia, and an example of the transition is Newtons writing career. A much earlier example is Galileo c,1600, some of whose scientific writings were in Latin, some in Italian, the latter to reach a wider audience. Likewise, in the early 18th century, French replaced Latin as a diplomatic language, at the same time, some were dismissing Latin as a useless accomplishment, unfit for a man of practical affairs. The last international treaty to be written in Latin was the Treaty of Vienna in 1738, a diminishing audience combined with diminishing production of Latin texts pushed Latin into a declining spiral from which it has not recovered
22.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
23.
Feedback
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Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself and this makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole. This action of feeding back of the signal output to input gave rise to the use of the term feedback as a distinct word by 1920. Over the years there has been dispute as to the best definition of feedback. According to Ashby, mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of circularity of action, for those with more practical aims, feedback should be a deliberate effect via some more tangible connection. Object to the definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum. Between its position and its momentum—a feedback that, from the point of view, is somewhat mystical. He emphasizes that the information by itself is not feedback unless translated into action, there are two types of feedback, positive feedback and negative feedback. As an example of feedback, the diagram might represent a cruise control system in a car, for example. The controlled system is the car, its input includes the combined torque from the engine, the cars speed is measured by a speedometer. The error signal is the departure of the speed as measured by the speedometer from the target speed and this measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine. The resulting change in torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed. The terms positive and negative were first applied to prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit, harold Stephen Blacks classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black, Positive feed-back increases the gain of the amplifier, according to Mindell confusion in the terms arose shortly after this. In contrast, Nyquist and Bode, when built on Black’s work. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition, the terms positive and negative feedback are defined in different ways within different disciplines. The altering of the gap between reference and actual values of a parameter, based on whether the gap is widening or narrowing
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. PMID 27974908.
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