1.
Blood vessel
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The blood vessels are the part of the circulatory system that transports blood throughout the human body. The word vascular, meaning relating to the vessels, is derived from the Latin vas. A few structures do not contain blood vessels and are labeled, tunica media, circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may be rich in smooth muscle, which controls the caliber of the vessel. Veins dont have the external elastic lamina, but only an internal one, tunica adventitia, entirely made of connective tissue. It also contains nerves that supply the vessel as well as nutrient capillaries in the blood vessels. Capillaries consist of more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of diffuse vascular supply it is called an anastomosis, anastomoses provide critical alternative routes for blood to flow in case of blockages. There is a layer of muscle surrounding the arteries and the veins which help contract and this creates enough pressure for blood to be pumped around the body. Blood vessels are part of the system, together with the heart. They are roughly grouped as arterial and venous, determined by whether the blood in it is flowing away from or toward the heart. The term arterial blood is used to indicate blood high in oxygen. This is because they are carrying the blood to and from the lungs, respectively, blood vessels do not actively engage in the transport of blood, but arteries—and veins to a degree—can regulate their inner diameter by contraction of the muscular layer. This changes the flow to downstream organs, and is determined by the autonomic nervous system. Vasodilation and vasoconstriction are also used antagonistically as methods of thermoregulation, oxygen is the most critical nutrient carried by the blood. In all arteries apart from the artery, hemoglobin is highly saturated with oxygen. In all veins apart from the vein, the hemoglobin is desaturated at about 75%. The blood pressure in blood vessels is traditionally expressed in millimetres of mercury, in the arterial system, this is usually around 120 mmHg systolic and 80 mmHg diastolic
2.
Smooth muscle
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Smooth muscle is an involuntary non-striated muscle. It is divided into two subgroups, the single-unit and multiunit smooth muscle, within single-unit cells, the whole bundle or sheet contracts as a syncytium. Single unit smooth muscle, however, is most common and lines blood vessels, the tract. Smooth muscle is different from skeletal muscle and cardiac muscle in terms of structure, function, regulation of contraction. Smooth muscle cells known as myocytes, have a shape and, like striated muscle, can tense. However, smooth muscle tissue tends to demonstrate greater elasticity and function within a larger length-tension curve than striated muscle and this ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. In the relaxed state, each cell is spindle-shaped, 20-500 micrometers in length, the smooth muscle is the only type of muscle without the ability to be voluntarily controlled in stressful situations. Myosin is primarily class II in smooth muscle, myosin II contains two heavy chains which constitute the head and tail domains. Each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, thus, myosin II has two heads. In smooth muscle, there is a gene that codes for the heavy chains myosin II. Also, smooth muscle may contain MHC that is not involved in contraction, myosin II also contains 4 light chains, resulting in 2 per head, weighing 20 and 17 kDa. These bind the chains in the neck region between the head and tail. The MLC20 is also known as the light chain and actively participates in muscle contraction. Two MLC20 isoforms are found in muscle, and they are encoded by different genes. The MLC17 is also known as the light chain. Its exact function is unclear, but its believed that it contributes to the stability of the myosin head along with MLC20. Two variants of MLC17 exist as a result of alternate splicing at the MLC17 gene, in the uterus, a shift in myosin expression has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle. The thin filaments that form part of the machinery are predominantly composed of α-
3.
Vein
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Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the back to the heart, exceptions are the pulmonary and umbilical veins. In contrast to veins, arteries carry blood away from the heart, veins are less muscular than arteries and are often closer to the skin. There are valves in most veins to prevent backflow, veins are present throughout the body as tubes that carry blood back to the heart. Veins are classified in a number of ways, including superficial vs. deep, pulmonary vs. systemic, superficial veins are those closer to the surface of the body, and have no corresponding arteries. Deep veins are deeper in the body and have corresponding arteries, perforator veins drain from the superficial to the deep veins. These are usually referred to in the limbs and feet. Communicating veins are veins that directly connect superficial veins to deep veins, pulmonary veins are a set of veins that deliver oxygenated blood from the lungs to the heart. Systemic veins drain the tissues of the body and deliver deoxygenated blood to the heart, most veins are equipped with valves to prevent blood flowing in the reverse direction. Veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the highly energetic blue wavelengths to penetrate through to the dark vein and reflect back to the viewer. The colour of a vein can be affected by the characteristics of a skin, how much oxygen is being carried in the blood. When a vein is drained of blood and removed from an organism, the largest veins in the human body are the venae cavae. These are two large veins which enter the right atrium of the heart from above and below. The superior vena cava carries blood from the arms and head to the atrium of the heart, while the inferior vena cava carries blood from the legs. The inferior vena cava is retroperitoneal and runs to the right, large veins feed into these two veins, and smaller veins into these. Together this forms the venous system, whilst the main veins hold a relatively constant position, the position of veins person to person can display quite a lot of variation. The pulmonary veins carry relatively oxygenated blood from the lungs to the heart, the superior and inferior venae cavae carry relatively deoxygenated blood from the upper and lower systemic circulations, respectively. The portal venous system is a series of veins or venules that directly connect two capillary beds, examples of such systems include the hepatic portal vein and hypophyseal portal system
4.
Artery
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Arteries are blood vessels that carry blood away from the heart. While most arteries carry oxygenated blood, there are two exceptions to this, the pulmonary and the umbilical arteries, the effective arterial blood volume is that extracellular fluid which fills the arterial system. The anatomy of arteries can be separated into gross anatomy, at the level, and microscopic anatomy. The outermost layer is known as the tunica externa, also known as tunica adventitia, inside this layer is the tunica media, or media, which is made up of smooth muscle cells and elastic tissue. The innermost layer, which is in contact with the flow of blood, is the tunica intima. This layer is made up of endothelial cells. The hollow internal cavity in which the flows is called the lumen. Arterial formation begins when endothelial cells begin to express specific genes. Arteries form part of the circulatory system and they carry blood that is oxygenated after it has been pumped from the heart. Arteries also aid the heart in pumping blood, arteries carry oxygenated blood away from the heart to the tissues, except for pulmonary arteries, which carry blood to the lungs for oxygenation. Veins and pulmonary veins carry deoxygenated blood. )The pulmonary artery carries blood from the heart to the lungs and it is unique because the blood in it is not oxygenated, as it has not yet passed through the lungs. The other unique artery is the artery, which carries deoxygenated blood from a fetus to its mother. Arteries have a blood pressure than other parts of the circulatory system. The pressure in arteries varies during the cardiac cycle and it is highest when the heart contracts and lowest when heart relaxes. The variation in pressure produces a pulse, which can be felt in different areas of the body, arterioles have the greatest collective influence on both local blood flow and on overall blood pressure. They are the primary adjustable nozzles in the system, across which the greatest pressure drop occurs. The larger arteries are generally elastic and the smaller ones tend to be muscular, systemic arteries deliver blood to the arterioles, and then to the capillaries, where nutrients and gases are exchanged. After travelling from the aorta, blood travels through peripheral arteries into smaller arteries called arterioles, arterioles help in regulating blood pressure by the variable contraction of the smooth muscle of their walls, and deliver blood to the capillaries
5.
Arteriole
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An arteriole /ɑːrˈtɪəri. oʊl/ is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls and are the site of vascular resistance. The greatest change in pressure and velocity of blood flow occurs at the transition of arterioles to capillaries. The decreased velocity of flow in the capillaries increases the blood pressure and this induces gas and nutrients to move from the blood to the cells, due to the lower osmotic pressure outside of the capillary. The opposite process occurs when the leaves the capillaries and enters the venules. Arterioles receive autonomic nervous system innervation and respond to various circulating hormones in order to regulate their diameter, retinal vessels lack a functional sympathetic innervation. Further local responses to stretch, carbon dioxide, pH, generally, norepinephrine and epinephrine are vasoconstrictive acting on alpha 1-adrenergic receptors. However, the arterioles of skeletal muscle, cardiac muscle, generally, stretch and high oxygen tension increase tone, and carbon dioxide and low pH promote vasodilation. Pulmonary arterioles are an exception as they vasodilate in response to high oxygen. Brain arterioles are particularly sensitive to pH with reduced pH promoting vasodilation, a number of hormones influence arteriole tone such as angiotensin II, endothelin, bradykinin, atrial natruretic peptide, and prostacyclin. An increase in the media to lumenal diameter ratio has been observed in hypertensive arterioles as the vascular wall thickens and/or lumenal diameter decreases, in a healthy vascular system the endothelium lines all blood-contacting surfaces, including arterioles, arteries, veins, capillaries, and heart chambers. In addition there is direct electrical and chemical communication via gap junctions between the cells and the vascular smooth muscle. Arteriole diameters decrease with age and with exposure to air pollution, any pathology which constricts blood flow, such as stenosis, will increase total peripheral resistance and lead to hypertension. Arteriolosclerosis is the term used for the hardening of arteriole walls. This can be due to decreased production from fibrinogen, associated with ageing. This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure, a metarteriole is an arteriole which bypasses capillary circulation
6.
Vasoconstriction
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Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels, the process is particularly important in staunching hemorrhage and acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased and this makes the skin turn paler because less blood reaches the surface, reducing the radiation of heat. On a larger level, vasoconstriction is one mechanism by which the body regulates, medications causing vasoconstriction, also known as vasoconstrictors, are one type of medicine used to raise blood pressure. Generalized vasoconstriction usually results in an increase in blood pressure. The extent of vasoconstriction may be slight or severe depending on the substance or circumstance, many vasoconstrictors also cause pupil dilation. Medications that cause vasoconstriction include, antihistamines, decongestants, and stimulants, severe vasoconstriction may result in symptoms of intermittent claudication. The mechanism that leads to results from the increased concentration of calcium within vascular smooth muscle cells. However, the mechanisms for generating an increased intracellular concentration of calcium depends on the vasoconstrictor. Smooth muscle cells are capable of generating action potentials, but this mechanism is utilized for contraction in the vasculature. Hormonal or pharmokinetic components are more physiologically relevant, two common stimuli for eliciting smooth muscle contraction are circulating epinephrine and activation of the sympathetic nervous system that directly innervates the muscle. These compounds interact with cell surface adrenergic receptors, the rise in intracellular calcium complexes with calmodulin, which in turn activates myosin light-chain kinase. This enzyme is responsible for phosphorylating the light chain of myosin to stimulate cross-bridge cycling and this reduction in calcium removes the stimulus necessary for contraction, allowing for a return to baseline. Factors that trigger vasoconstriction can be of exogenous or endogenous origin, ambient temperature is an example of the former. Cutaneous vasoconstriction will occur because of the exposure to the severe cold. Examples of endogenous factors include the nervous system, circulating hormones. Examples include amphetamines, antihistamines and cocaine, many are used in medicine to treat hypotension and as topical decongestants. Vasoconstrictors are also used clinically to increase blood pressure or to reduce blood flow
7.
Hemodynamics
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Hemodynamics or hæmodynamics is the dynamics of blood flow. The circulatory system is controlled by mechanisms, much as hydraulic circuits are controlled by control systems. Hemodynamic response continuously monitors and adjusts to conditions in the body, thus hemodynamics explains the physical laws that govern the flow of blood in the blood vessels. Blood is a fluid, best studied using rheology rather than hydrodynamics. Blood vessels are not rigid tubes, so classic hydrodynamics and fluids mechanics based on the use of classical viscometers are not capable of explaining hemodynamics, Blood is composed of plasma and formed elements. The plasma contains 91. 5% water, 7% proteins and 1. 5% other solutes, normal blood plasma behaves like a Newtonian fluid at physiological rates of shear. Typical values for the viscosity of human plasma at 37 °C is 1.4 mN·s/m2. The osmotic pressure of solution is determined by the number of particles present, for example, a 1 molar solution of a substance contains 7023602200000000000♠6. 022×1023 molecules per liter of that substance and at 0 °C it has an osmotic pressure of 2.27 MPa. The osmotic pressure of the plasma affects the mechanics of the circulation in several ways, an alteration of the osmotic pressure difference across the membrane of a blood cell causes a shift of water and a change of cell volume. The changes in shape and flexibility affect the properties of whole blood. This in turn affects the mechanics of the whole blood, the red blood cell is highly flexible and biconcave in shape. Its membrane has a Youngs modulus in the region of 106 Pa, deformation in red blood cells is induced by shear stress. When a suspension is sheared, the red blood cells deform and spin because of the velocity gradient, with the rate of deformation and spin depending on the shear-rate and this can influence the mechanics of the circulation and may complicate the measurement of blood viscosity. From the above equation we can see that the velocity of the particle depends on the square of the radius. If the particle is released from rest in the fluid, its sedimentation velocity Us increases until it attains the value called the terminal velocity. We have looked at blood flow and blood composition, before we look at the main issue, hemodilution, let us take a brief history into the use of blood. Its therapeutic use is not a modern phenomenon, egyptian writings dates back at least 2000 years suggest oral ingestion of blood as a ‘sovereign remedy’ for leprosy. However, the use of blood comes with significant risks
8.
Tissue (biology)
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In biology, tissue is a cellular organizational level intermediate between cells and a complete organ. A tissue is an ensemble of similar cells from the origin that together carry out a specific function. Organs are then formed by the grouping together of multiple tissues. The study of tissue is known as histology or, in connection with disease, the classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in microscopy, immunofluorescence. With these tools, the appearances of tissues can be examined in health and disease. Animal tissues are grouped into four types, connective, muscle, nervous. Collections of tissues joined in structural units to serve a common function compose organs, while all animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular type may differ developmentally for different classifications of animals. By contrast, a true epithelial tissue is present only in a layer of cells held together via occluding junctions called tight junctions. This tissue covers all surfaces that come in contact with the external environment such as the skin, the airways. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina and they are made up of cells separated by non-living material, which is called an extracellular matrix. This matrix can be liquid or rigid, for example, blood contains plasma as its matrix and bones matrix is rigid. Connective tissue gives shape to organs and holds them in place, blood, bone, tendon, ligament, adipose and areolar tissues are examples of connective tissues. One method of classifying tissues is to divide them into three types, fibrous connective tissue, skeletal connective tissue, and fluid connective tissue. Muscle cells form the active contractile tissue of the known as muscle tissue or muscular tissue. Muscle tissue functions to force and cause motion, either locomotion or movement within internal organs. Cells comprising the nervous system and peripheral nervous system are classified as nervous tissue
9.
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
10.
Organ (anatomy)
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In biology, an organ or viscus is a collection of tissues joined in a structural unit to serve a common function. In anatomy, a viscus is an organ, and viscera is the plural form. Organs are composed of main tissue, parenchyma, and sporadic tissues, the main tissue is that which is unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, and connective tissues. The main tissues that make up an organ tend to have common embryologic origins, functionally related organs often cooperate to form whole organ systems. Organs exist in all biological organisms, in particular they are not restricted to animals. In single-cell organisms like bacteria, the analogue of an organ is called organelle. A hollow organ is an organ that forms a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity. Two or more organs working together in the execution of a specific body function form an organ system, the functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via an organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system, the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Mammals such as humans have a variety of organ systems and these specific systems are also widely studied in human anatomy. Cardiovascular system, pumping and channeling blood to and from the body and lungs with heart, digestive system, digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum and anus. Excretory system, kidneys, ureters, bladder and urethra involved in balance, electrolyte balance. Integumentary system, skin, hair and nails, nervous system, collecting, transferring and processing information with brain, spinal cord and nerves. Reproductive system, the sex organs, such as ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, prostate, respiratory system, the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm. Skeletal system, structural support and protection with bones, cartilage, ligaments, the organ level of organisation in animals can be first detected in flatworms and the more advanced phyla. The less-advanced taxa do not show consolidation of their tissues into organs, 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 vegetative and reproductive, vegetative plant organs are roots, stems, and leaves
11.
Metabolism
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Metabolism is the set of life-sustaining chemical transformations within the cells of living organisms. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, usually, breaking down releases energy and building up consumes energy. The chemical reactions of metabolism are organized into metabolic pathways, in one chemical is transformed through a series of steps into another chemical. Enzymes act as catalysts that allow the reactions to proceed more rapidly, enzymes also allow the regulation of metabolic pathways in response to changes in the cells environment or to signals from other cells. The metabolic system of a particular organism determines which substances it will find nutritious, for example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The speed of metabolism, the rate, influences how much food an organism will require. A striking feature of metabolism is the similarity of the metabolic pathways. These striking similarities in metabolic pathways are likely due to their appearance in evolutionary history. Most of the structures that make up animals, plants and microbes are made from three classes of molecule, amino acids, carbohydrates and lipids. These biochemicals can be joined together to make such as DNA and proteins. Proteins are made of amino acids arranged in a linear chain joined together by peptide bonds, many proteins are enzymes that catalyze the chemical reactions in metabolism. Other proteins have structural or mechanical functions, such as those that form the cytoskeleton, Proteins are also important in cell signaling, immune responses, cell adhesion, active transport across membranes, and the cell cycle. Lipids are the most diverse group of biochemicals and their main structural uses are as part of biological membranes both internal and external, such as the cell membrane, or as a source of energy. Lipids are usually defined as hydrophobic or amphipathic biological molecules but will dissolve in organic solvents such as benzene or chloroform, the fats are a large group of compounds that contain fatty acids and glycerol, a glycerol molecule attached to three fatty acid esters is called a triacylglyceride. Several variations on this structure exist, including alternate backbones such as sphingosine in the sphingolipids. Steroids such as cholesterol are another class of lipids. Carbohydrates are aldehydes or ketones, with hydroxyl groups attached. Carbohydrates are the most abundant biological molecules, and fill numerous roles, such as the storage and transport of energy, the basic carbohydrate units are called monosaccharides and include galactose, fructose, and most importantly glucose
12.
Drug
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A drug is any substance that, when inhaled, injected, smoked, consumed, absorbed via a patch on the skin, or dissolved under the tongue, causes a physiological change in the body. In pharmacology, a drug, also called a medication or medicine, is a chemical substance used to treat, cure, prevent. Traditionally drugs were obtained through extraction from plants, but more recently also by organic synthesis. Pharmaceutical drugs may be used for a duration, or on a regular basis for chronic disorders. Another major classification system is the Biopharmaceutics Classification System and this classifies drugs according to their solubility and permeability or absorption properties. Psychoactive drugs are chemical substances that affect the function of the nervous system, altering perception. They include alcohol, a depressant, and the nicotine and caffeine. These three are the most widely consumed psychoactive drugs worldwide and are also considered recreational drugs since they are used for rather than medicinal purposes. Other recreational drugs include hallucinogens, opiates and amphetamines and some of these are used in spiritual or religious settings. Some drugs can cause addiction and all drugs can have side effects, excessive use of stimulants can promote stimulant psychosis. Many recreational drugs are illicit and international such as the Single Convention on Narcotic Drugs exist for the purpose of their prohibition. The transitive verb to drug arose later and invokes the psychoactive rather than properties of a substance. A medication or medicine is a drug taken to cure or ameliorate any symptoms of an illness or medical condition, the use may also be as preventive medicine that has future benefits but does not treat any existing or pre-existing diseases or symptoms. In the United Kingdom, behind-the-counter medicines are called pharmacy medicines which can only be sold in registered pharmacies and these medications are designated by the letter P on the label. The range of medicines available without a prescription varies from country to country, medications are typically produced by pharmaceutical companies and are often patented to give the developer exclusive rights to produce them. Those that are not patented are called generic drugs since they can be produced by other companies without restrictions or licenses from the patent holder, pharmaceutical drugs are usually categorised into drug classes. A group of drugs will share a chemical structure, or have the same mechanism of action. Another major classification system is the Biopharmaceutics Classification System and this groups drugs according to their solubility and permeability or absorption properties
13.
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
14.
Dioxygen in biological reactions
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Dioxygen plays an important role in the energy metabolism of living organisms. Free oxygen is produced in the biosphere through photolysis of water during photosynthesis in cyanobacteria, green algae, during oxidative phosphorylation in cellular respiration, oxygen is reduced to water, thus closing the biological water-oxygen redox cycle. In nature, free oxygen is produced by the splitting of water during oxygenic photosynthesis. Green algae and cyanobacteria in marine environments provide about 70% of the oxygen produced on earth. The remainder is produced by plants, although for example. Photosytem II therefore has also referred to as water-plastoquinone oxido-reductase. The protons from the water molecules are released into the thylakoid lumen. The O2 remaining after oxidation of the molecule is released into the atmosphere. Water oxidation is catalyzed by an enzyme complex known as the oxygen evolving complex or water-splitting complex found associated with the lumenal side of thylakoid membranes. Manganese is an important cofactor, and calcium and chloride are also required for the reaction to occur, in vertebrates, oxygen uptake is carried out by the following processes, Oxygen diffuses through membranes and into red blood cells after inhalation into the lungs. They are bound to dioxygen complexes, which are compounds that contain O2 as a ligand. In blood, the group of hemoglobin binds oxygen when it is present. Vertebrate animals use hemoglobin in their blood to transport oxygen from their lungs to their tissues, a liter of blood can dissolve 200 cc of oxygen gas, which is much more than water can dissolve. After being carried in blood to a tissue in need of oxygen, O2 is handed-off from the heme group to monooxygenase. Monooxygenase uses oxygen to catalyze many reactions in the body. Carbon dioxide, a product, is released from the cell and into the blood. Blood circulates back to the lungs and the process repeats, molecular oxygen, O2, is essential for cellular respiration in all aerobic organisms. Oxygen is used as an acceptor in mitochondria to generate chemical energy in the form of adenosine triphosphate during oxidative phosphorylation
15.
Lipid
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In biology, lipids comprise a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signaling, lipids have applications in the cosmetic and food industries as well as in nanotechnology. Biological lipids originate entirely or in part from two types of biochemical subunits or building-blocks, ketoacyl and isoprene groups. Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides, lipids also encompass molecules such as fatty acids and their derivatives, as well as other sterol-containing metabolites such as cholesterol. Although humans and other mammals use various biosynthetic pathways both to break down and to synthesize lipids, some essential lipids cannot be made this way, the word lipid stems etymologically from the Greek lipos. The fatty acid structure is one of the most fundamental categories of biological lipids, the carbon chain, typically between four and 24 carbons long, may be saturated or unsaturated, and may be attached to functional groups containing oxygen, halogens, nitrogen, and sulfur. If a fatty acid contains a double bond, there is the possibility of either a cis or trans geometric isomerism, cis-double bonds cause the fatty acid chain to bend, an effect that is compounded with more double bonds in the chain. This in turn plays an important role in the structure and function of cell membranes, most naturally occurring fatty acids are of the cis configuration, although the trans form does exist in some natural and partially hydrogenated fats and oils. Examples of biologically important fatty acids include the eicosanoids, derived primarily from arachidonic acid and eicosapentaenoic acid, that include prostaglandins, leukotrienes, docosahexaenoic acid is also important in biological systems, particularly with respect to sight. Other major lipid classes in the fatty acid category are the fatty esters, fatty esters include important biochemical intermediates such as wax esters, fatty acid thioester coenzyme A derivatives, fatty acid thioester ACP derivatives and fatty acid carnitines. The fatty amides include N-acyl ethanolamines, such as the cannabinoid neurotransmitter anandamide, glycerolipids are composed of mono-, di-, and tri-substituted glycerols, the best-known being the fatty acid triesters of glycerol, called triglycerides. The word triacylglycerol is sometimes used synonymously with triglyceride, in these compounds, the three hydroxyl groups of glycerol are each esterified, typically by different fatty acids. Because they function as a store, these lipids comprise the bulk of storage fat in animal tissues. The hydrolysis of the bonds of triglycerides and the release of glycerol. Additional subclasses of glycerolipids are represented by glycosylglycerols, which are characterized by the presence of one or more sugar residues attached to glycerol via a glycosidic linkage, examples of structures in this category are the digalactosyldiacylglycerols found in plant membranes and seminolipid from mammalian sperm cells. Glycerophospholipids, usually referred to as phospholipids, are ubiquitous in nature and are key components of the bilayer of cells, as well as being involved in metabolism. Neural tissue contains high amounts of glycerophospholipids, and alterations in their composition has been implicated in various neurological disorders. Examples of glycerophospholipids found in biological membranes are phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine, the major sphingoid base of mammals is commonly referred to as sphingosine
16.
Adenosine
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Adenosine is a purine nucleoside composed of a molecule of adenine attached to a ribose sugar molecule moiety via a β-N9-glycosidic bond. It is also a neuromodulator, believed to play a role in promoting sleep, Adenosine also plays a role in regulation of blood flow to various organs through vasodilation. Common side effects include chest pain, feeling faint, shortness of breath along with tingling of the senses, serious side effects include a worsening dysrhythmia and low blood pressure. It appears to be safe in pregnancy, when it is administered intravenously, adenosine causes transient heart block in the atrioventricular node. It also causes endothelial-dependent relaxation of smooth muscle as is found inside the artery walls and this causes dilation of the normal segments of arteries, i. e. where the endothelium is not separated from the tunica media by atherosclerotic plaque. This feature allows physicians to use adenosine to test for blockages in the coronary arteries, the administration of adenosine also reduces blood flow to coronary arteries past the occlusion. Other coronary arteries dilate when adenosine is administered while the segment past the occlusion is already maximally dilated and this leads to less blood reaching the ischemic tissue, which in turn produces the characteristic chest pain. In individuals suspected of suffering from a supraventricular tachycardia, adenosine is used to identify the rhythm. Certain SVTs can be terminated with adenosine. This includes any re-entrant arrhythmias that require the AV node for the re-entry, e. g. AV reentrant tachycardia, in addition, atrial tachycardia can sometimes be terminated with adenosine. Fast rhythms of the heart that are confined to the atria or ventricles, however, the ventricular response rate is temporarily slowed with adenosine in such cases. Because of the effects of adenosine on AV node-dependent SVTs, adenosine is considered a class V antiarrhythmic agent, when adenosine is used to cardiovert an abnormal rhythm, it is normal for the heart to enter ventricular asystole for a few seconds. This can be disconcerting to a conscious patient, and is associated with angina-like sensations in the chest. Adenosine is used an adjunct to thallous chloride TI201 or Tc99m myocardial perfusion scintigraphy in patients unable to undergo adequate stress testing with exercise, due to adenosines extremely short half-life, the IV line is started as proximal to the heart as possible, such as the antecubital fossa. The IV push is often followed with a flush of 10-20 ccs of saline. If this has no effect, a dose of 12 mg can be given 1–2 minutes after the first dose, some clinicians may prefer to administer a higher dose, rather than repeat a dose that apparently had no effect. When given to dilate the arteries, such as in a stress test, the recommended dose may be increased in patients on theophylline, since methylxanthines prevent binding of adenosine at receptor sites. The dose is often decreased in patients on dipyridamole and diazepam because adenosine potentiates the effects of these drugs
17.
Interstitial fluid
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Interstitial fluid or tissue fluid is a solution that bathes and surrounds the tissue cells of multicellular animals. It is the component of the extracellular fluid, which also includes plasma. The interstitial fluid is found in the interstices - the spaces between cells, on average, a person has about 10 litres of interstitial fluid, providing the cells of the body with nutrients and a means of waste removal. Plasma and interstitial fluid are very similar and this similarity exists because water, ions, and small solutes are continuously exchanged between plasma and interstitial fluids across the walls of capillaries. Plasma, the component in blood, communicates freely with interstitial fluid through pores. Hydrostatic pressure is generated by the force of the heart. It pushes water out of the capillaries, the water potential is created due to the inability of certain blood proteins to pass through the walls of capillaries. The build-up of these proteins within the capillaries induces osmosis, the water passes from a high concentration outside of the vessels to a low concentration inside of the vessels, in an attempt to reach an equilibrium. The osmotic pressure drives water back into the vessels, because the blood in the capillaries is constantly flowing, equilibrium is never reached. The balance between the two forces differs at different points on the capillaries, at the arterial end of a vessel, the hydrostatic pressure is greater than the osmotic pressure, so the net movement favors water and other solutes being passed into the tissue fluid. At the venous end, the pressure is greater, so the net movement favors substances being passed back into the capillary. This difference is created by the direction of the flow of blood, to prevent a build-up of tissue fluid surrounding the cells in the tissue, complementing the venous system is the lymphatic system, which plays a part in the transport of tissue fluid. Tissue fluid can pass into the lymph vessels, and eventually ends up rejoining the blood. Sometimes the removal of fluid does not function correctly. This can cause swelling, often around the feet and ankles, the position of swelling is due to the effects of gravity. Interstitial fluid consists of a solvent containing sugars, salts, fatty acids, amino acids, coenzymes, hormones, neurotransmitters, white blood cells. This water solvent accounts for 26% of the water in the human body, the composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood. This means that tissue fluid has a different composition in different tissues, not all of the contents of the blood pass into the tissue, which means that tissue fluid and blood are not the same
18.
Capillary
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Capillaries are the smallest of a bodys blood vessels that make up the microcirculation. Their endothelial linings are only one layer thick. Lymph capillaries connect with larger vessels to drain lymph collected in the microcirculation. The term angiogenesis denotes the formation of new capillaries from pre-existing blood vessels, blood flows from the heart through arteries, which branch and narrow into arterioles, and then branch further into capillaries where nutrients and wastes are exchanged. The capillaries then join and widen to become venules, which in turn widen and converge to become veins, capillaries do not function on their own, but instead in a capillary bed, an interweaving network of capillaries supplying organs and tissues. The more metabolically active a cell or environment is, the capillaries are required to supply nutrients. Metarterioles are found primarily in the mesenteric microcirculation and were thought to be present in most or all capillary beds. The physiological mechanisms underlying precapillary resistance is no longer considered to be a result of precapillary sphincters outside of the mesentery organ, lymphatic capillaries are slightly larger in diameter than blood capillaries, and have closed ends. This structure permits interstitial fluid to flow into them but not out, lymph capillaries have a greater internal oncotic pressure than blood capillaries, due to the greater concentration of plasma proteins in the lymph. However lipid-soluble molecules can diffuse through the endothelial cell membranes along concentration gradients. Tight junctions can be divided into two subtypes, Those with numerous transport vesicles, which are found primarily in skeletal muscles, fingers, gonads. Those with few vesicles, which are found in the central nervous system. These capillaries are a constituent of the blood–brain barrier, fenestrated capillaries have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse. In the renal glomerulus there are cells with no diaphragms, called foot processes or pedicels. Both of these types of vessels have continuous basal laminae and are primarily located in the endocrine glands, intestines, pancreas. Sinusoidal capillaries are a type of open-pore capillary, that have larger openings in the endothelium. These types of blood vessels allow red and white cells and various serum proteins to pass. These capillaries lack pinocytotic vesicles, and therefore utilize gaps present in cell junctions to permit transfer between cells, and hence across the membrane
19.
Precapillary sphincter
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A precapillary sphincter is a band of smooth muscle that adjusts blood flow into capillaries mainly in the mesenteric microcirculation. At the point where each of the capillaries originates from an arteriole and this is called the precapillary sphincter. The sphincter can open and close the entrance to the capillary, the entire capillary bed may be bypassed by blood flow through arteriovenous anastomoses or through preferential flow through metarterioles. If the sphincter is damaged or cannot contract, blood can flow into the bed at high pressures. When capillary pressures are high, fluid passes out of the capillaries into the interstitial space, precapillary sphincters and metarterioles were discovered in the mesenteric circulation in the 1950s. Medical and physiological textbooks, such as Guyton, Boron and Fulton, etc. were quick to claim the existence of said sphincters and metarterioles all over the body, at least since 1976 there has been considerable debate about the existence of precapillary sphincters and metarterioles. As of 2013 it is held that they are unique to the mesenteric circulation, baez S, Feldman SM, Gootman PM. Central neural influence on precapillary microvessels and sphincter
20.
Cardiac output
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Cardiac output, is a term used in cardiac physiology that describes the volume of blood being pumped by the heart, in particular by a left or right ventricle, per unit time. CO values can be represented using many physical units, such as dm3/min and L/min, because cardiac output is related to the quantity of blood delivered to various parts of the body, it is an important indicator of how efficiently the heart can meet the demands of the body. For instance, infections are correlated with high CO and heart failure with low CO, along with stroke volume, cardiac output is a global blood flow parameter of interest in hæmodynamics – the study of the flow of blood under external forces. The factors affecting stroke volume and heart rate also affect cardiac output, the figure to the right illustrates this dependency and lists some of these factors. A detailed hierarchical illustration is provided in a subsequent figure, there are many methods of measuring CO, both invasively and non-invasively, each with its own advantages and drawbacks. No standard or reference measurement against which all of these methods can be compared exists, the function of the heart is to drive blood through the circulatory system in a cycle that delivers oxygen, nutrients and chemicals to the bodys cells and removes cellular waste. This is detailed in equation below, there are a number of clinical methods to measure cardiac output, ranging from direct intracardiac catheterisation to non-invasive measurement of the arterial pulse. Each method has advantages and drawbacks, relative comparison is limited by the absence of a widely accepted gold standard measurement. Cardiac output can also be affected significantly by the phase of respiration – intra-thoracic pressure changes influence diastolic filling and this is especially important during mechanical ventilation, in which cardiac output can vary by up to 50% across a single respiratory cycle. Cardiac output should therefore be measured at evenly spaced points over a cycle or averaged over several cycles. Invasive methods are accepted, but there is increasing evidence that these methods are neither accurate nor effective in guiding therapy. Consequently, the focus on development of methods is growing. This method uses ultrasound and the Doppler effect to measure cardiac output, the blood velocity through the heart causes a Doppler shift in the frequency of the returning ultrasound waves. Echocardiography is a method of quantifying cardiac output using ultrasound. Two-dimensional ultrasound and Doppler measurements are used together to calculate cardiac output, the result is then multiplied by the heart rate to obtain cardiac output. Although used in medicine, it has a wide test-retest variability. It is said to require training and skill, but the exact steps needed to achieve clinically adequate precision have never been disclosed. 2D measurement of the valve diameter is one source of noise, others are beat-to-beat variation in stroke volume
21.
Systole
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Systole /ˈsɪstəliː/ is the part of the cardiac cycle when the ventricles contract. The term systole originates from New Latin, from Ancient Greek συστολή, from συστέλλειν, the mammalian heart has 4 chambers, the left atrium, the left ventricle, the right atrium and the right ventricle. When the smaller, upper atria chambers contract in late diastole, when the lower chambers are filled and the valves to the atria are closed, the ventricles undergo isovolumetric contraction, marking the first stage of systole. The second phase of systole sends blood from the ventricle to the aorta and body extremities. Thus, the atria and ventricles contract in alternating sequence, the left and right atria feed blood, at the same time, into the ventricles. Then, the left and right ventricles contract simultaneously as well, cardiac systole is the contraction of the cardiac muscle in response to an electrochemical stimulus to the hearts cells. The cardiac output is the volume of blood pumped by the ventricle in one minute. The ejection fraction is the volume of blood pumped divided by the volume of blood in the left ventricle. Cardiac electrical systole is staged and first derived from sympathetic charge from the sinoatrial node, electrical systole opens voltage-gated sodium, potassium and calcium channels. A rise in intracellular calcium triggers the interaction of actin and myosin in the presence of ATP that generates force, the muscular contraction of myocardium generates an active stress that increases intra-ventricular pressure and when intra-ventricular pressure exceeds aortic pressure there is ejection of blood. Mechanical systole is the origin of the pulse, the pulse is readily palpated at many points on the body and represents a universally accepted tactile method of observing peak or systolic blood pressure. Mechanical forces resulting from electrical systole cause rotation of the mass around the long and short axes. Atrial systole represents the contraction of myocardium of the left and right atria, atrial systole occurs late in ventricular diastole. One force driving blood from the atria to the ventricles is the decrease in pressure that occurs during ventricular diastole. The drop in pressure that occurs during ventricular diastole allows the atrioventricular valves to open. Loss of normal electrical conduction in the heart, as seen during atrial fibrillation, atrial flutter, contraction of the atria follows depolarization, represented by the P wave of the ECG. At the start of systole, the ventricles are normally filled with approximately 70–80 percent of their capacity due to inflow during diastole. Atrial contraction, also referred to as the kick, contributes the remaining 20–30 percent of filling
22.
Diastole
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Diastole /daɪˈæstəliː/ is the part of the cardiac cycle when the heart refills with blood following systole. Ventricular diastole is the period during which the ventricles are filling and relaxing, the term diastole originates from the Greek word διαστολη, meaning dilation. Diastole is closely related to the phenomenon of recoil within ballistics, during ventricular diastole, the pressure in the ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the ventricular filling velocity or flow into the ventricles have two main components, First an early diastolic one caused ventricular suction, and second, a late one created by atrial contraction. The E/A ratio can be used as a measure, since it is reduced in diastolic dysfunction. Early diastole, i. e. the E-wave in the E/A ratio, is a suction mechanism. In late diastole, i. e. the A-wave, as the left and right atria contract and this is known as atrial kick. 80% of the blood flows passively down to the ventricles during the E-wave active suction period, the adjective diastolic is used to refer to filling of the heart with blood between muscle contractions. It is used to describe the portion of the cardiac cycle related to contraction. More typically it is used as one component of measurement of blood pressure, diastolic pressure refers to the lowest pressure within the arterial bloodstream occurring during each heartbeat. The other component of pressure is systolic pressure, which refers to the highest arterial pressure during each heartbeat. When blood pressure is stated for medical purposes, it is written as a seeming ratio of systolic to diastolic pressure, for example. This is not intended to be read as a ratio and for the vast majority of purposes cannot be read as a ratio. It is not a display of a numerator over a denominator, examining diastolic function during a cardiac stress test is a good way to test for heart failure with preserved ejection fraction. Brain natriuretic peptide is a cardiac neurohormone secreted from ventricular myocytes at the end of diastole, increased BNP concentrations have been found in patients who experience diastolic heart failure
23.
Heart rate
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Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute. The heart rate can vary according to the physical needs, including the need to absorb oxygen. It is usually equal or close to the pulse measured at any peripheral point, activities that can provoke change include physical exercise, sleep, anxiety, stress, illness, and ingestion of drugs. Many texts cite the normal resting adult heart rate range from 60–100 bpm. Tachycardia is a fast heart rate, defined as above 100 bpm at rest, bradycardia is a slow heart rate, defined as below 60 bpm at rest. Several studies, as well as expert consensus indicates that the normal resting heart rate is probably closer to a range between 50–90 bpm. During sleep a slow heartbeat with rates around 40–50 bpm is common and is considered normal, when the heart is not beating in a regular pattern, this is referred to as an arrhythmia. Abnormalities of heart rate sometimes indicate disease, while heart rhythm is regulated entirely by the sinoatrial node under normal conditions, heart rate is regulated by sympathetic and parasympathetic input to the sinoatrial node. Therefore, stimulation of the accelerans nerve increases heart rate, while stimulation of the nerve decreases it. Due to individuals having a constant blood volume, one of the ways to deliver more oxygen to an organ is to increase heart rate to permit blood to pass by the organ more often. Normal resting heart rates range from 60–100 bpm, bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people, tachycardia is defined as a resting heart rate above 100 bpm, though persistent rest rates between 80–100 bpm, mainly if they are present during sleep, may be signs of hyperthyroidism or anemia. Central nervous system such as substituted amphetamines increase heart rate. Central nervous system depressants or sedatives decrease the heart rate, there are many ways in which the heart rate speeds up or slows down. Most involve stimulant-like endorphins and hormones being released in the brain, many of which are those that are forced/enticed out by the ingestion and this section discusses target heart rates for healthy persons and are inappropriately high for most persons with coronary artery disease. The heart rate is generated by the sinoatrial node. It is also influenced by central factors through sympathetic and parasympathetic nerves, nervous influence over the heartrate is centralized within the two paired cardiovascular centres of the medulla oblongata. During rest, both centers provide slight stimulation to the heart, contributing to autonomic tone and this is a similar concept to tone in skeletal muscles
24.
Stroke volume
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In cardiovascular physiology, stroke volume is the volume of blood pumped from the left ventricle per beat. The term stroke volume can apply to each of the two ventricles of the heart, although it refers to the left ventricle. The stroke volumes for each ventricle are generally equal, both being approximately 70 mL in a healthy 70-kg man, because stroke volume decreases in certain conditions and disease states, stroke volume itself correlates with cardiac function. Its value is obtained by subtracting end-systolic volume from end-diastolic volume for a given ventricle. S V = E D V − E S V In a healthy 70-kg man, ESV is approximately 50 mL and EDV is approximately 120mL, stroke work refers to the work, or pressure of the blood multiplied by the stroke volume. Men, on average, have higher volumes than women due to the larger size of their hearts. However, stroke volume depends on factors such as heart size, contractility, duration of contraction, preload. Prolonged aerobic exercise training may also increase stroke volume, which results in a lower heart rate. Reduced heart rate prolongs ventricular diastole, increasing volume. Stroke volume is controlled by preload. An increase in the volume or speed of venous return will increase preload and, through the Frank–Starling law of the heart, decreased venous return has the opposite effect, causing a reduction in stroke volume. Though not usually affecting stroke volume in healthy individuals, increased afterload will hinder the ventricles in ejecting blood, increased afterload may be found in aortic stenosis and arterial hypertension. Similar to cardiac index, is a method of relating the stroke volume to the size of the person Body surface area. S V I = S V B S A = B S A = C O H R × B S A Berne, Robert M. Levy, cS1 maint, Multiple names, authors list Boron, Walter F. Boulpaep, Emile L. Medical Physiology, A Cellular and Molecular Approach, cS1 maint, Multiple names, authors list The Gross Physiology of the Cardiovascular System The Determinants of Cardiac Output
25.
Warm-blooded
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Warm-blooded animal species can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a body temperature by regulating metabolic processes. The only known homeotherms are birds and mammals, other species have various degrees of thermoregulation. In general, warm-bloodedness refers to three categories of thermoregulation. Endothermy is the ability of creatures to control their body temperatures through internal means such as muscle shivering or increasing their metabolism. Some writers restrict the meaning of endothermy to mechanisms that raise the animals metabolic rate to produce heat. The opposite of endothermy is ectothermy, homeothermy maintains a stable internal body temperature regardless of external influence and temperatures. The stable internal temperature is higher than the immediate environment. Tachymetabolism maintains a high resting metabolism, in essence, tachymetabolic creatures are on all the time. Though their resting metabolism is still many times slower than their active metabolism, tachymetabolic creatures have greater difficulty dealing with a scarcity of food. A large proportion of the creatures traditionally called warm-blooded, like birds and mammals, however, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many bats and small birds are poikilothermic and bradymetabolic when they sleep for the night, for these creatures, the term heterothermy was coined. Some fish have warm-blooded characteristics, such as the opah, swordfish and some sharks have circulatory mechanisms that keep their brains and eyes above ambient temperatures and thus increase their ability to detect and react to prey. Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed, body heat is generated by metabolism. This refers to the chemical reactions cells use to break down glucose into water and carbon dioxide and, in so doing, generate ATP, a high-energy compound used to power other cellular processes. Muscle contraction is a type of process that generates heat energy. All organisms metabolize food and other inputs, but some make use of the output than others. Like all energy conversions, metabolism is rather inefficient, and around 60% of the energy is converted to heat rather than to ATP
26.
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
27.
Endothelial cells
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It is a thin layer of simple squamous cells called endothelial cells. Endothelial cells in contact with blood are called vascular endothelial cells. Vascular endothelial cells line the entire system, from the heart to the smallest capillaries. These cells have unique functions in vascular biology and these functions include fluid filtration, such as in the glomerulus of the kidney, blood vessel tone, hemostasis, neutrophil recruitment, and hormone trafficking. Endothelium of the surfaces of the heart chambers is called endocardium. Both blood and lymphatic capillaries are composed of a layer of endothelial cells called a monolayer. In straight sections of a vessel, vascular endothelial cells typically align. Many considered the endothelium a specialized epithelial tissue, excessive or prolonged increases in permeability of the endothelial monolayer, as in cases of chronic inflammation, may lead to tissue edema/swelling. The most prevailing mechanism of endothelial dysfunction is an increase in reactive oxygen species, the signalling protein ERK5 is essential for maintaining normal endothelial cell function
28.
Nitric oxide
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Nitric oxide is a molecular, chemical compound with chemical formula of ·NO. One of several oxides of nitrogen, it is a gas under standard conditions. Nitric oxide is a free radical—i. e and its bonding structure includes an unpaired electron, represented by the dot on the nitrogen atom—and it is in the class of heteronuclear diatomic molecules that are of historic theoretical interest. It is an important intermediate in the chemical industry. It is also produced naturally by the high air temperatures produced along the path of lightning in thunderstorms. In mammals including humans, nitric oxide is an important cellular signaling molecule involved in physiological and pathological processes. It is a powerful vasodilator with a short half-life of a few seconds in the blood, long-known pharmaceuticals such as nitroglycerine and amyl nitrite were found to be precursors to nitric oxide more than a century after their first use in medicine. Low levels of nitric oxide production are important in protecting organs such as the liver from ischemic damage, Nitric oxide production is associated with nonalcoholic fatty liver disease and is essential for hepatic lipid metabolism under starvation. As a consequence of its importance in neuroscience, physiology, and immunology, research into its function led to the 1998 Nobel Prize for discovering the role of nitric oxide as a cardiovascular signalling molecule. It is classified as a hazardous substance in the United States as defined in Section 302 of the U. S. Emergency Planning and Community Right-to-Know Act, and is subject to reporting requirements by facilities which produce, store. When exposed to oxygen, nitric oxide is converted into nitrogen dioxide,2 ·NO + O2 →2 NO2 This conversion has been speculated as occurring via the ONOONO intermediate. In water, nitric oxide reacts with oxygen and water to form HNO2 or nitrous acid, nitrosyl iodide can form but is an extremely short-lived species and tends to reform I2. 2 ·NO + Cl2 →2 NOCl Nitroxyl is the form of nitric oxide. Nitric oxide dimer N2O2 is formed when nitric oxide is cooled, Nitric oxide can also react directly with sodium methoxide, forming sodium formate and nitrous oxide. So-called NONOate compounds are used for nitric oxide generation. Nitric oxide reacts with all metals to give complexes called metal nitrosyls. The most common bonding mode of nitric oxide is the linear type
29.
Autonomic nervous system
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The autonomic nervous system is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of internal organs. This system is the mechanism in control of the fight-or-flight response. Within the brain, the nervous system is regulated by the hypothalamus. Autonomic functions include control of respiration, cardiac regulation, vasomotor activity and those are then subdivided into other areas and are also linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the stem, acts as an integrator for autonomic functions. The autonomic nervous system has two branches, the nervous system and the parasympathetic nervous system. The sympathetic nervous system is considered the fight or flight system. In many cases, both of these systems have opposite actions where one system activates a response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as excitory and inhibitory was overturned due to the many exceptions found, there are inhibitory and excitatory synapses between neurons. Although the ANS is also known as the nervous system. Most autonomous functions are involuntary but they can work in conjunction with the somatic nervous system which provides voluntary control. The autonomic nervous system is divided into the nervous system. The sympathetic division emerges from the cord in the thoracic and lumbar areas. The parasympathetic division has craniosacral “outflow”, meaning that the neurons begin at the cranial nerves, the preganglionic, or first, neuron will begin at the “outflow” and will synapse at the postganglionic, or second, neuron’s cell body. The postganglionic neuron will then synapse at the target organ, the sympathetic nervous system consists of cells with bodies in the lateral grey column from T1 to L2/3. These cell bodies are GVE neurons and are the preganglionic neurons, the parasympathetic nervous system consists of cells with bodies in one of two locations, the brainstem or the sacral spinal cord. These sensory neurons monitor the levels of carbon dioxide, oxygen and sugar in the blood, arterial pressure and they also convey the sense of taste and smell, which, unlike most functions of the ANS, is a conscious perception. Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, primary sensory neurons project onto “second order” visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract, that integrates all visceral information
30.
Catecholamine
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A catecholamine is a monoamine, an organic compound that has a catechol and a side-chain amine. Catechol can be either a molecule or a substituent of a larger molecule. Catecholamines are derived from the amino acid tyrosine, which is derived from sources as well as synthesis of phenylalanine. Catecholamines are water-soluble and are 50%-bound to plasma proteins in circulation, included among catecholamines are epinephrine, norepinephrine, and dopamine. Release of the hormones epinephrine and norepinephrine from the medulla of the adrenal glands is part of the fight-or-flight response. Tyrosine is created from phenylalanine by hydroxylation by the enzyme phenylalanine hydroxylase, tyrosine is also ingested directly from dietary protein. Catecholamine-secreting cells use several reactions to convert tyrosine serially to L-DOPA, depending on the cell type, dopamine may be further converted to norepinephrine or even further converted to epinephrine. Various stimulant drugs are catecholamine analogues, catecholamines have the distinct structure of a benzene ring with two hydroxyl groups, an intermediate ethyl chain, and a terminal amine group. Phenylethanolamines such as norepinephrine have a group on the ethyl chain. Catecholamines are produced mainly by the cells of the adrenal medulla. The similarly neuromelanin-pigmented cell bodies of the locus ceruleus produce norepinephrine, dopamine is the first catecholamine synthesized from DOPA. In turn, norepinephrine and epinephrine are derived from metabolic modification of dopamine. The enzyme dopamine hydroxylase requires copper as a cofactor and DOPA decarboxylase requires PLP, the rate limiting step in catecholamine biosynthesis through the predominant metabolic pathway is the hydroxylation of L-tyrosine to L-DOPA. Catecholamine synthesis is inhibited by alpha-methyl-p-tyrosine, which inhibits tyrosine hydroxylase, catecholamines have a half-life of a few minutes when circulating in the blood. They can be degraded either by methylation by catechol-O-methyltransferases or by deamination by monoamine oxidases, mAOIs bind to MAO, thereby preventing it from breaking down catecholamines and other monoamines. Two catecholamines, norepinephrine and dopamine, act as neuromodulators in the nervous system. The catecholamine norepinephrine is a neuromodulator of the sympathetic nervous system but is also present in the blood. In emergency medicine, this occurrence is known as catecholamine dump
31.
Norepinephrine
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Norepinephrine, also called noradrenaline or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter. Norepinephrine is also the international nonproprietary name given to the drug, regardless of which name is used for the substance itself, parts of the body that produce or are affected by it are referred to as noradrenergic. In the brain, norepinephrine is produced in closely packed brain cell neurons or nuclei that are small yet exert powerful effects on brain areas. The most important of these nuclei is the locus coeruleus, located in the pons, regardless of how and where it is released, norepinephrine acts on target cells by binding to and activating noradrenergic receptors located on the cell surface. The general function of norepinephrine is to mobilize the brain and body for action, norepinephrine release is lowest during sleep, rises during wakefulness, and reaches much higher levels during situations of stress or danger, in the so-called fight-or-flight response. In the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, a variety of medically important drugs work by altering the actions of norepinephrine systems. Norepinephrine itself is used as an injectable drug for the treatment of critically low blood pressure. Beta blockers, which some of the effects of norepinephrine, are frequently used to treat glaucoma, migraine. Alpha blockers, which counter a different set of effects, are used to treat several cardiovascular. Alpha-2 agonists often have an effect, and are commonly used as anesthesia-enhancers in surgery. Many important psychiatric drugs exert strong effects on systems in the brain. Norepinephrine is a catecholamine and a phenethylamine and its structure differs from that of epinephrine only in that epinephrine has a methyl group attached to its nitrogen, whereas the methyl group is replaced by a hydrogen atom in norepinephrine. The prefix nor- is derived as an abbreviation of the word normal, norepinephrine is synthesized from the amino acid tyrosine by a series of enzymatic steps in the adrenal medulla and postganglionic neurons of the sympathetic nervous system. These amino acids are found in nearly every protein and, as such, are provided by ingestion of protein-containing food, phenylalanine is converted into tyrosine by the enzyme phenylalanine hydroxylase, with molecular oxygen and tetrahydrobiopterin as cofactors. Tyrosine is converted into L-DOPA by the tyrosine hydroxylase, with tetrahydrobiopterin, O2. L-DOPA is converted into dopamine by the enzyme aromatic L-amino acid decarboxylase, dopamine is then converted into norepinephrine by the enzyme dopamine β-monooxygenase, with O2 and ascorbic acid as cofactors. Norepinephrine itself can further be converted into epinephrine by the enzyme phenylethanolamine N-methyltransferase with S-adenosyl-L-methionine as cofactor, in mammals, norepinephrine is rapidly degraded to various metabolites. The initial step in the breakdown can be catalyzed by either of the monoamine oxidase or COMT
32.
Epinephrine
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Epinephrine, also known as adrenalin or adrenaline, is a hormone, neurotransmitter and medication. Epinephrine is normally produced by both the adrenal glands and certain neurons and it plays an important role in the fight-or-flight response by increasing blood flow to muscles, output of the heart, pupil dilation, and blood sugar. It does this by binding to alpha and beta receptors and it is found in many animals and some one cell organisms. Jokichi Takamine first isolated epinephrine in 1901, as a medication it is used to treat a number of conditions, including anaphylaxis, cardiac arrest, and superficial bleeding. Inhaled epinephrine may be used to improve the symptoms of croup and it may also be used for asthma when other treatments are not effective. It is given intravenously, by injection into a muscle, by inhalation, common side effects include shakiness, anxiety, and sweating. A fast heart rate and high pressure may occur. Occasionally it may result in a heart rhythm. While the safety of its use during pregnancy and breastfeeding is unclear, the adrenal medulla is a minor contributor to total circulating catecholamines, though it contributes over 90% of circulating epinephrine. Little epinephrine is found in tissues, mostly in scattered chromaffin cells. Following adrenalectomy, epinephrine disappears below the limit in the blood stream. The adrenals contribute about 7% of circulating norepinephrine, most of which is a spill over from neurotransmission with little activity as a hormone, pharmacological doses of epinephrine stimulate α1, α2, β1, β2, and β3 adrenoceptors of the sympathetic nervous system. Sympathetic nerve receptors are classified as adrenergic, based on their responsiveness to adrenaline, the term adrenergic is often misinterpreted in that the main sympathetic neurotransmitter is norepinephrine, rather than epinephrine, as discovered by Ulf von Euler in 1946. Epinephrine does have a β2 adrenoceptor-mediated effect on metabolism and the airway, the concept of the adrenal medulla and the sympathetic nervous system being involved in the flight, fight and fright response was originally proposed by Cannon. But the adrenal medulla, in contrast to the cortex, is not required for survival. In adrenalectomized patients hemodynamic and metabolic responses to such as hypoglycemia. One physiological stimulus to epinephrine secretion is exercise and this was first demonstrated using the denervated pupil of a cat as an assay, later confirmed using a biological assay on urine samples. Biochemical methods for measuring catecholamines in plasma were published from 1950 onwards, the development of extraction methods and enzyme-isotope derivate radio-enzymatic assays transformed the analysis down to a sensitivity of 1 pg for epinephrine
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Phosphorylation
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Phosphorylation is the addition of a phosphoryl group − to a molecule. In biology, phosphorylation and its counterpart, dephosphorylation, are critical for cellular processes. A large fraction of proteins are at least temporarily phosphorylated, as are many sugars, lipids, Phosphorylation is especially important for protein function as this modification activates many enzymes, thereby regulating their function. Protein phosphorylation is one type of post-translational modification, the prominent role of protein phosphorylation in biochemistry is illustrated by the huge body of studies published on the subject. Phosphorylation of sugars is often the first stage of their catabolism and it allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter. Phosphorylation of glucose is a key reaction in sugar metabolism because many sugars are first converted to glucose before they are metabolized further. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by D-glucose + ATP -> D-glucose-6-phosphate + ADP ΔG° = -16.7 kJ/mol, the two enzymes have been identified as a specific glucokinase and non-specific hexokinase. Hepatic cell is freely permeable to glucose, and the rate of phosphorylation of glucose is the rate-limiting step in glucose metabolism by the liver. The role of glucose 6-phosphate in glycogen synthase, High blood glucose concentration causes an increase in levels of glucose 6 phosphate in liver, skeletal muscle. In liver, synthesis of glycogen is directly correlated by blood glucose concentration and in muscle and adipocytes. High blood glucose releases insulin, stimulating the trans location of specific glucose transporters to the cell membrane, the hexokinase enzyme has a low Km, indicating a high affinity for glucose, so this initial phosphorylation can proceed even when glucose levels at nanoscopic scale within the blood. The phosphorylation of glucose can be enhanced by the binding of Fructose-6-phosphate, fructose consumed in the diet is converted to F1P in the liver. This negates the action of F6P on glucokinase, which favors the forward reaction. The capacity of cells to phosphorylate fructose exceeds capacity of metabolize fructose-1-phosphate. Consuming excess fructose ultimately results in an imbalance in liver metabolism, Phosphorylation of glucose is imperative in processes within the body. For example, phosphorylating glucose is necessary for insulin-dependent mechanistic target of rapamycin pathway activity within the heart and this further suggests a link between intermediary metabolism and cardiac growth. Reversible phosphorylation of proteins is an important regulatory mechanism occurs in both prokaryotic and eukaryotic organisms. Kinases phosphorylate proteins and phosphatases dephosphorylate proteins, many enzymes and receptors are switched on or off by phosphorylation and dephosphorylation
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Myosin
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Myosins comprise a superfamily of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other motility processes in eukaryotes. They are responsible for actin-based motility, the term was originally used to describe a group of similar ATPases found in the cells of both striated muscle tissue and smooth muscle tissue. Following the discovery by Pollard and Korn of enzymes with myosin-like function in Acanthamoeba castellanii, virtually all eukaryotic cells contain myosin isoforms. Some isoforms have specialized functions in cell types, while other isoforms are ubiquitous. The structure and function of myosin is strongly conserved across species, most myosin molecules are composed of a head, neck, and tail domain. The head domain binds the actin, and uses ATP hydrolysis to generate force. The neck domain acts as a linker and as an arm for transducing force generated by the catalytic motor domain. The neck domain can also serve as a site for myosin light chains which are distinct proteins that form part of a macromolecular complex. The tail domain generally mediates interaction with cargo molecules and/or other myosin subunits, in some cases, the tail domain may play a role in regulating motor activity. Multiple myosin II molecules generate force in skeletal muscle through a power stroke mechanism fuelled by the energy released from ATP hydrolysis, the power stroke occurs at the release of phosphate from the myosin molecule after the ATP hydrolysis while myosin is tightly bound to actin. The effect of release is a conformational change in the molecule that pulls against the actin. The release of the ADP molecule leads to the rigor state of myosin. The binding of a new ATP molecule will release myosin from actin, ATP hydrolysis within the myosin will cause it to bind to actin again to repeat the cycle. The combined effect of the power strokes causes the muscle to contract. The wide variety of genes found throughout the eukaryotic phyla were named according to different schemes as they were discovered. The nomenclature can therefore be somewhat confusing when attempting to compare the functions of proteins within. Skeletal muscle myosin, the most conspicuous of the myosin superfamily due to its abundance in muscle fibers, was the first to be discovered and this protein makes up part of the sarcomere and forms macromolecular filaments composed of multiple myosin subunits. Similar filament-forming myosin proteins were found in muscle, smooth muscle
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Dephosphorylation
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Dephosphorylation is the removal of a phosphate group from an organic compound by hydrolysis. It is a reversible post-translational modification, dephosphorylation and its counterpart, phosphorylation, activate and deactivate enzymes by detaching or attaching phosphoric esters and anhydrides. A notable occurrence of dephosphorylation is the conversion of ATP to ADP, dephosphorylation employs a type of hydrolytic enzyme, or hydrolase, which cleave ester bonds. The prominent hydrolase subclass used in dephosphorylation is phosphatase, phosphatase removes phosphate groups by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group. The reversible phosphorylation-dephosphorylation reaction occurs in every physiological process, making proper function of protein phosphases necessary for organism viability, because protein dephosphorylation is a key process involved in cell signalling, protein phosphatases are implicated in conditions such as cardiac disease, diabetes, and Alzheimers disease. The discovery of dephosphorylation came from a series of experiments examining the enzyme phosphorylase isolated from rabbit skeletal muscle. In 1955, Edwin Krebs and Edmond Fischer used radiolabeled ATP to determine that phosphate is added to the residue of phosphorylase to convert it from its b to a form via phosphorylation. Subsequently, Krebs and Fischer showed that this phosphorylation is part of a kinase cascade, finally, after purifying the phosphorylated form of the enzyme, phosphorylase a, from rabbit liver, ion exchange chromatography was used to identify phosphoprotein phosphatase I and II. Edwin Krebs and Edmond Fischer won the 1992 Nobel Prize in Physiology or Medicine for the discovery of reversible protein phosphorylation, phosphorylation involves the covalent modification of the hydroxyl with a phosphate group through the nucleophilic attack of the alpha phosphate in ATP by the oxygen in the hydroxyl. Dephosphorylation involves removal of the group through a hydration reaction by addition of a molecule of water and release of the original phosphate group. Both processes are reversible and either mechanism can be used to activate or deactivate a protein, phosphorylation of a protein produces many biochemical effects, such as changing its conformation to alter its binding to a specific ligand to increase or reduce its activity. Phosphorylation and dephosphorylation can be used on all types of substrates, such as proteins, enzymes, membrane channels, signaling molecules. The sum of these processes is referred to as phosphoregulation, the deregulation of phosphorylation can lead to disease. During the synthesis of proteins, polypeptide chains, which are created by ribosomes translating mRNA, the dephosphorylation of proteins is a mechanism for modifying behavior of a protein, often by activating or inactivating an enzyme. Components of the protein synthetic apparatus also undergo phosphorylation and dephosphorylation, as part of postranslational modifications, phosphate groups may be removed from serine, threonine, or tyrosine. As such, pathways of signal transduction depend on sequential phosphorylation and dephosphorylation of a wide variety of proteins. ATP4− + H2O --> ADP3− + HPO42− + H+ Adenosine triphosphate, or ATP, in a spontaneous dephosphorylation reaction 30.5 kJ/mol is released, which is harnessed to drive cellular reactions. Overall, nonspontaneous reactions coupled to the dephosphorylation of ATP are spontaneous and this is important in driving oxidative phosphorylation
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Myosin-light-chain phosphatase
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Myosin light-chain phosphatase, more commonly called myosin phosphatase, is an enzyme that dephosphorylates the regulatory light chain of myosin II. This dephosphorylation reaction occurs in muscle tissue and initiates the relaxation process of the muscle cells. Thus, myosin phosphatase undoes the muscle contraction process initiated by myosin light-chain kinase, the enzyme is composed of three subunits, the catalytic region, the myosin binding subunit, and a third subunit of unknown function. The catalytic region uses two manganese ions as catalysts to dephosphorylate the light-chains on myosin, which causes a change in the myosin. The enzyme is conserved and is found in all organisms’ smooth muscle tissue. Smooth muscle tissue is made of actin and myosin, two proteins that interact together to produce muscle contraction and relaxation. Myosin II, also known as myosin, has two heavy chains that consist of the head and tail domains and four light chains that bind to the heavy chains in the “neck” region. When the muscle needs to contract, calcium ions flow into the cytosol from the reticulum, where they activate calmodulin. MLC kinase phosphorylates the light chain at the Ser-19 residue. This phosphorylation causes a change in the myosin, activating crossbridge cycling and causing the muscle to contract. Because myosin undergoes a change, the muscle will stay contracted even if calcium. The conformational change must be undone to relax the muscle, when myosin phosphatase binds to myosin, it removes the phosphate group. Without the group, the myosin reverts to its original conformation, in which it cannot interact with the actin and hold the muscle tense, the muscle will remain in this relaxed position until myosin is phosphorylated by MLC kinase and undergoes a conformational change. Myosin phosphatase is made of three subunits, because it is so important to basic cellular functions, and because there are far fewer protein phosphatases than kinases in cells, PP1’s structure and function is highly conserved. PP1 works by using two manganese ions as catalysts for the dephosphorylation, surrounding these ions is a Y-shaped cleft with three grooves, a hydrophobic, an acidic, and a C-terminal groove. When PP1 is not bonded to any other subunit, it is not particularly specific, however, when it bonds to the second subunit of myosin phosphatase, MYPT1, this catalytic cleft changes configuration. This results in an increase in myosin specificity. Thus, it is clear that MYPT1 has great power over PP1 and myosin phosphatase
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Symporter
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A symporter is an integral membrane protein that is involved in the transport of many differing types of molecules across the cell membrane. The symporter works in the membrane and molecules are transported across the cell membrane at the same time, and is, therefore. The transporter is called a symporter, because the molecules will travel in the direction in relation to each other. This is in contrast to the antiport transporter, typically, the ion will move down the electrochemical gradient, allowing the other molecule to move against the concentration gradient. The movement of the ion across the membrane is facilitated diffusion, sGLT1 in the intestinal epithelium transports sodium ions and glucose across luminal membrane of the epithelial cells so that it can be absorbed into the bloodstream. This is the basis of oral rehydration therapy, if this symporter did not exist, individual sodium channels and glucose uniporters would not be able to transfer glucose against the concentration gradient and into the bloodstream. Na+/K+/2Cl− symporter in the loop of Henle in the tubules of the kidney transports 4 molecules of 3 different types, a sodium ion. Loop diuretics such as furosemide act on this protein, marine invertebrates use symporters to transport against strong chemical gradients. Amino acids and sugars are taken up from sea water in the presence of sodium and is driven by the NA+/K+-ATPase pump. In the roots of plants, the H+/K+ symporters are only one member of a group of several symporters/antiporters that specifically allow only one charged hydrogen ion and this group of carriers all contribute to modulate the chemiosmotic potential inside the cell. Initially H+ is pumped into the area outside the root by H+ ATPase, the reasons for this are twofold. For one, substances in nature have a tendency to move from areas of concentration to areas of low concentration. It does not aggregate, but begins to move from the highly concentrated areas to the areas of low concentration, second, large groups of predominantly positively charged or negatively charged particles will naturally repel each other. This is demonstrated by attempting to push the two poles or two negative poles of a magnet together. Depending on the strength of the magnet, the repulsion may be so strong that it is impossible to push the magnets together unless aided by machinery. Proton motive force does work on the system by bringing ions back towards the epidermis of the root or surface of a root hair along with the protons, cotransport Cotransporter Uniporter Antiporter Symporters at the US National Library of Medicine Medical Subject Headings
