Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is water, contains proteins, mineral ions, carbon dioxide, blood cells themselves. Albumin is the main protein in plasma, it functions to regulate the colloidal osmotic pressure of blood; the blood cells are red blood cells, white blood cells and platelets. The most abundant cells in vertebrate blood are red blood cells; these contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and increasing its solubility in blood. In contrast, carbon dioxide is transported extracellularly as bicarbonate ion transported in plasma. Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated.
Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune system, based on white blood cells. White blood cells help to resist parasites. Platelets are important in the clotting of blood. Arthropods, using hemolymph, have hemocytes as part of their immune system. Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.
Medical terms related to blood begin with hemo- or hemato- from the Greek word αἷμα for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen. Blood performs many important functions within the body, including: Supply of oxygen to tissues Supply of nutrients such as glucose, amino acids, fatty acids Removal of waste such as carbon dioxide and lactic acid Immunological functions, including circulation of white blood cells, detection of foreign material by antibodies Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding Messenger functions, including the transport of hormones and the signaling of tissue damage Regulation of core body temperature Hydraulic functions Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m3 close to pure water's density of 1000 kg/m3.
The average adult has a blood volume of 5 litres, composed of plasma and several kinds of cells. These blood cells consist of erythrocytes and thrombocytes. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, white cells about 0.7%. Whole blood exhibits non-Newtonian fluid dynamics. If all human hemoglobin were free in the plasma rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function effectively. One microliter of blood contains: 4.7 to 6.1 million, 4.2 to 5.4 million erythrocytes: Red blood cells contain the blood's hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals; the red blood cells are marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit, is about 45%; the combined surface area of all red blood cells of the human body would be 2,000 times as great as the body's exterior surface.
4,000–11,000 leukocytes: White blood cells are part of the body's immune system. The cancer of leukocytes is called leukemia. 200,000 -- 500,000 thrombocytes: Also called platelets. Fibrin from the coagulation cascade creates a mesh over the platelet plug. About 55% of blood is blood plasma, a fluid, the blood's liquid medium, which by itself is straw-yellow in color; the blood plasma volume totals of 2.7–3.0 liters in an average human. It is an aqueous solution containing 92% water, 8% blood plasma proteins, trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose, amino acids, fatty acids, removes waste products, such as carbon dioxide and lactic acid. Other important components include: Serum albumin Blood-clotting factors Immunoglobulins lipoprotein particles Various
Nitric oxide is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical, i.e. it has an unpaired electron, sometimes denoted by a dot in its chemical formula, i.e. ·NO. Nitric oxide is a heteronuclear diatomic molecule, a historic class that drew researches which spawned early modern theories of chemical bonding. An important intermediate in chemical industry, nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide is a signaling molecule in many physiological and pathological processes, it was proclaimed the "Molecule of the Year" in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule. Nitric oxide should not be confused with nitrous oxide, an anesthetic, or with nitrogen dioxide, a brown toxic gas and a major air pollutant. Upon condensing to a liquid, nitric oxide dimerizes to dinitrogen dioxide, but the association is weak and reversible.
The N–N distance in crystalline NO is 218 pm, nearly twice the N–O distance. Since the heat of formation of ·NO is endothermic, NO can be decomposed to the elements. Catalytic converters in cars exploit this reaction: 2 NO → O2 + N2; when exposed to oxygen, nitric oxide converts 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 water to form nitrous acid; the reaction is thought to proceed via the following stoichiometry: 4 NO + O2 + 2 H2O → 4 HNO2. Nitric oxide reacts with fluorine and bromine to form the nitrosyl halides, such as nitrosyl chloride: 2 NO + Cl2 → 2 NOCl. With NO2 a radical, NO combines to form the intensely blue dinitrogen trioxide: NO + NO2 ⇌ ON−NO2; the addition of a nitric oxide moiety to another molecule is referred to as nitrosylation. Nitric oxide reacts with acetone and an alkoxide to a diazeniumdiolate or nitrosohydroxylamine and methyl acetate: This reaction, discovered around 1898, remains of interest in nitric oxide prodrug research.
Nitric oxide can react directly with sodium methoxide, forming sodium formate and nitrous oxide. Nitric oxide reacts with transition metals to give complexes called metal nitrosyls; the most common bonding mode of nitric oxide is the terminal linear type. Alternatively, nitric oxide can serve as a one-electron pseudohalide. In such complexes, the M−N−O group is characterized by an angle between 120° and 140°; the NO group can bridge between metal centers through the nitrogen atom in a variety of geometries. In commercial settings, nitric oxide is produced by the oxidation of ammonia at 750–900 °C with platinum as catalyst: 4 NH3 + 5 O2 → 4 NO + 6 H2OThe uncatalyzed endothermic reaction of oxygen and nitrogen, effected at high temperature by lightning has not been developed into a practical commercial synthesis: N2 + O2 → 2 NO In the laboratory, nitric oxide is conveniently generated by reduction of dilute nitric acid with copper: 8 HNO3 + 3 Cu → 3 Cu2 + 4 H2O + 2 NOAn alternative route involves the reduction of nitrous acid in the form of sodium nitrite or potassium nitrite: 2 NaNO2 + 2 NaI + 2 H2SO4 → I2 + 4 NaHSO4 + 2 NO 2 NaNO2 + 2 FeSO4 + 3 H2SO4 → Fe23 + 2 NaHSO4 + 2 H2O + 2 NO 3 KNO2 + KNO3 + Cr2O3 → 2 K2CrO4 + 4 NOThe iron sulfate route is simple and has been used in undergraduate laboratory experiments.
So-called NONOate compounds are used for nitric oxide generation. Nitric oxide concentration can be determined using a chemiluminescent reaction involving ozone. A sample containing nitric oxide is mixed with a large quantity of ozone; the nitric oxide reacts with the ozone to produce oxygen and nitrogen dioxide, accompanied with emission of light: NO + O3 → NO2 + O2 + hνwhich can be measured with a photodetector. The amount of light produced is proportional to the amount of nitric oxide in the sample. Other methods of testing include electroanalysis, where ·NO reacts with an electrode to induce a current or voltage change; the detection of NO radicals in biological tissues is difficult due to the short lifetime and concentration of these radicals in tissues. One of the few practical methods is spin trapping of nitric oxide with iron-dithiocarbamate complexes and subsequent detection of the mono-nitrosyl-iron complex with electron paramagnetic resonance. A group of fluorescent dye indicators that are available in acetylated form for intracellular measurements exist.
The most common compound is 4,5-diaminofluorescein. Nitric oxide reacts with the hydroperoxy radical to form nitrogen dioxide, which can react with a hydroxyl radical to produce nitric acid: ·NO + HO2•→ •NO2 + •OH ·NO2 + •OH → HNO3Nitric acid, along with sulfuric acid, contribute acid rain deposition. Furthermore, ·NO participates in ozone layer depletion. In this process, nitric oxide reacts with stratospheric ozone to form O2 and nitrogen dioxide: ·NO + O3 → NO2 + O2As seen in the Concentration Measurement section, this reaction is utilized to measure concentrations of ·NO in control volumes; as seen in the Acid deposition section, nitric oxide can transform into nitrogen dioxide. Symptoms of short-term nitrogen dioxide exposure include nausea and headache. Long-term effects could include impaired respiratory function. NO is a gaseous signaling molecule, it is a key vertebrate biological messenger. It is
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head close to the sensory organs for senses such as vision; the brain is the most complex organ in a vertebrate's body. In a human, the cerebral cortex contains 14–16 billion neurons, the estimated number of neurons in the cerebellum is 55–70 billion; each neuron is connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. Physiologically, the function of the brain is to exert centralized control over the other organs of the body; the brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows coordinated responses to changes in the environment.
Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain. The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. Recent models in modern neuroscience treat the brain as a biological computer different in mechanism from an electronic computer, but similar in the sense that it acquires information from the surrounding world, stores it, processes it in a variety of ways; this article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates. It deals with the human brain insofar; the ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context.
The most important is brain disease and the effects of brain damage, that are covered in the human brain article. The shape and size of the brain varies between species, identifying common features is difficult. There are a number of principles of brain architecture that apply across a wide range of species; some aspects of brain structure are common to the entire range of animal species. The simplest way to gain information about brain anatomy is by visual inspection, but many more sophisticated techniques have been developed. Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, sliced apart for examination of the interior. Visually, the interior of the brain consists of areas of so-called grey matter, with a dark color, separated by areas of white matter, with a lighter color. Further information can be gained by staining slices of brain tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations.
It is possible to examine the microstructure of brain tissue using a microscope, to trace the pattern of connections from one brain area to another. The brains of all species are composed of two broad classes of cells: neurons and glial cells. Glial cells come in several types, perform a number of critical functions, including structural support, metabolic support and guidance of development. Neurons, are considered the most important cells in the brain; the property that makes neurons unique is their ability to send signals to specific target cells over long distances. They send these signals by means of an axon, a thin protoplasmic fiber that extends from the cell body and projects with numerous branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body; the length of an axon can be extraordinary: for example, if a pyramidal cell of the cerebral cortex were magnified so that its cell body became the size of a human body, its axon magnified, would become a cable a few centimeters in diameter, extending more than a kilometer.
These axons transmit signals in the form of electrochemical pulses called action potentials, which last less than a thousandth of a second and travel along the axon at speeds of 1–100 meters per second. Some neurons emit action potentials at rates of 10–100 per second in irregular patterns. Axons transmit signals to other neurons by means of specialized junctions called synapses. A single axon may make as many as several thousand synaptic connections with other cells; when an action potential, traveling along an axon, arrives at a synapse, it causes a chemical called a neurotransmitter to be released. The neurotransmitter binds to receptor molecules in the membrane of the target cell. Synapses are the key functional elements of the brain; the essential function of the brain is cell-to-cell communication, synapses are the points at which communication occurs. The human brain has been estimated to contain 100 trillion synapses; the functions of these synapses are diverse: some are excitatory.
In medicine, a pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the neck, wrist, at the groin, behind the knee, near the ankle joint, on foot. Pulse is equivalent to measuring the heart rate; the heart rate can be measured by listening to the heart beat by auscultation, traditionally using a stethoscope and counting it for a minute. The radial pulse is measured using three fingers; this has a reason: the finger closest to the heart is used to occlude the pulse pressure, the middle finger is used get a crude estimate of the blood pressure, the finger most distal to the heart is used to nullify the effect of the ulnar pulse as the two arteries are connected via the palmar arches. The study of the pulse is known as sphygmology. Claudius Galen was the first physiologist to describe the pulse; the pulse is an expedient tactile method of determination of systolic blood pressure to a trained observer.
Diastolic blood pressure is non-palpable and unobservable by tactile methods, occurring between heartbeats. Pressure waves generated by the heart in systole move the arterial walls. Forward movement of blood occurs when the boundaries are compliant; these properties form enough to create a palpable pressure wave. The heart rate may be lesser than the pulse rate depending upon physiologic demand. In this case, the heart rate is determined by auscultation or audible sounds at the heart apex, in which case it is not the pulse; the pulse deficit is determined by simultaneous palpation at the radial artery and auscultation at the PMI, near the heart apex. It may be present in case of atrial fibrillation. Pulse velocity, pulse deficits and much more physiologic data are and simplistically visualized by the use of one or more arterial catheters connected to a transducer and oscilloscope; this invasive technique has been used in intensive care since the 1970s. The rate of the pulse is observed and measured by tactile or visual means on the outside of an artery and is recorded as beats per minute or BPM.
The pulse may be further indirectly observed under light absorbances of varying wavelengths with assigned and inexpensively reproduced mathematical ratios. Applied capture of variances of light signal from the blood component hemoglobin under oxygenated vs. deoxygenated conditions allows the technology of pulse oximetry. Normal pulse rates at rest, in beats per minute: The pulse rate can be used to check overall heart health and fitness level. Lower is better, but bradycardias can be dangerous. Symptoms of a dangerously slow heartbeat include loss of energy and fainting. A normal pulse is regular in force. An irregular pulse may be due to sinus arrhythmia, ectopic beats, atrial fibrillation, paroxysmal atrial tachycardia, atrial flutter, partial heart block etc. Intermittent dropping out of beats at pulse is called "intermittent pulse". Examples of regular intermittent pulse include pulsus bigeminus, second-degree atrioventricular block. An example of irregular intermittent pulse is atrial fibrillation.
The degree of expansion displayed by artery during diastolic and systolic state is called volume. It is known as amplitude, expansion or size of pulse. A weak pulse signifies narrow pulse pressure, it may be due to low cardiac output, valvular heart disease etc. A bounding pulse signifies high pulse pressure, it may be due to low peripheral resistance, increased cardiac output, increased stroke volume, decreased distensibility of arterial system. The strength of the pulse can be reported: 0 = Absent 1 = Barely palpable 2 = Easily palpable 3 = Full 4 = Aneurysmal or bounding pulse Also known as compressibility of pulse, it is a rough measure of systolic blood pressure. It corresponds to diastolic blood pressure. A low tension pulse, the vessel is impalpable between beats. In high tension pulse, vessels feel rigid between pulse beats. A form or contour of a pulse is palpatiory estimation of arteriogram. A rising and falling pulse is seen in aortic regurgitation. A slow rising and falling pulse is seen in aortic stenosis.
Comparing pulses and different places gives valuable clinical information. A discrepant or unequal pulse between left and right radial artery is observed in anomalous or aberrant course of artery, coarctation of aorta, dissecting aneurysm, peripheral embolism etc. An unequal pulse between upper and lower extremities is seen in coarctation to aorta, block at bifurcation of aorta, dissection of aorta, iatrogenic trauma and arteriosclerotic obstruction. A normal artery is not palpable after flattening by digital pressure. A thick radial artery, palpable 7.5–10 cm up the forearm is suggestive of arteriosclerosis. In coarctation of aorta, femoral pulse may be delayed as compared to radial pulse
Organs are groups of tissues with similar functions. Plant and animal life relies on many organs. Organs are composed of main tissue, "sporadic" tissues, stroma; the main tissue is that, unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, connective tissues. The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer. Functionally-related organs cooperate to form whole organ systems. Organs exist in most multicellular organisms. In single-celled organisms such as bacteria, the functional analogue of an organ is known as an organelle. In plants there are three main organs. A hollow organ is an internal organ that forms a hollow tube, or pouch such as the stomach, intestine, or bladder. In the study of anatomy, the term viscus is used to refer to an internal organ, viscera is the plural form. 79 organs have been identified in the human body. In biology, tissue is a cellular organizational level between complete organs.
A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant morphology. Classical tools for studying tissues include the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis. Two or more organs working together in the execution of a specific body function form an organ system called a biological system or body system.
The functions of organ systems share significant overlap. For instance, the nervous and endocrine system both operate via the hypothalamus. For this reason, the two systems are studied as the neuroendocrine system; the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Common organ system designations in plants includes the differentiation of root. All parts of the plant above ground, including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system. Animals such as humans have a variety of organ systems; these specific systems are widely studied in human anatomy. Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart and blood vessels. Digestive system: digestion and processing food with salivary glands, stomach, gallbladder, intestines, colon and anus. Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid and adrenals, i.e. adrenal glands.
Excretory system: kidneys, ureters and urethra involved in fluid balance, electrolyte balance and excretion of urine. Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, adenoids and spleen. Integumentary system: skin and nails of mammals. Scales of fish and birds, feathers of birds. Muscular system: movement with muscles. Nervous system: collecting and processing information with brain, spinal cord and nerves. Reproductive system: the sex organs, such as ovaries, fallopian tubes, vulva, testes, vas deferens, seminal vesicles and penis. Respiratory system: the organs used for breathing, the pharynx, trachea, bronchi and diaphragm. Skeletal system: structural support and protection with bones, cartilage and tendons; the study of plant organs is referred to as plant morphology, rather than anatomy – as in animal systems.
Organs of plants can be divided into reproductive. Vegetative plant organs include roots and leaves; the reproductive organs are variable. In flowering plants, they are represented by the flower and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions of plants, the reproductive organs are called strobili, in Lycopodiophyta, or gametophores in mosses; the vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis, while the reproductive organs are essential in reproduction. However, if there is asexual vegetative reproduction, the vegetative organs are those that create the new generation of plants. Many societies have a system for organ donation, in which a living or deceased donor's organ is transplanted into a person with a failing organ; the transplantation of larger solid organs requires immunosuppression to prevent organ rejection or graft-versus-host disease.
There is considerable interest throughout the world in creating laboratory-grown or artificial organs. The English word "organ" dates back in reference to any musical instrument. By the late 14th
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
In haemodynamics, the body must respond to physical activities, external temperature, other factors by homeostatically adjusting its blood flow to deliver nutrients such as oxygen and glucose to stressed tissues and allow them to function. Haemodynamic response allows the rapid delivery of blood to active neuronal tissues. Since higher processes in the brain occur constantly, cerebral blood flow is essential for the maintenance of neurons and other cells of the brain. In order to understand how blood is delivered to cranial tissues, it is important to understand the vascular anatomy of the space itself. Large cerebral arteries in the brain split into smaller arterioles known as pial arteries; these consist of endothelial cells and smooth muscle, as these pial arteries further branch and run deeper into the brain, they associate with glial cells, namely astrocytes and pericytes. The intracerebral arterioles and capillaries are unlike systemic arterioles and capillaries in that they do not allow substances to diffuse through them.
Endothelial cells, smooth muscle, neurons and pericytes work together in the brain order to maintain the BBB while still delivering nutrients to tissues and adjusting blood flow in the intracranial space to maintain homeostasis. As they work as a functional unit, alterations in their interactions at the cellular level can impair HR in the brain and lead to deviations in normal nervous function. Various cell types play a role in HR, including astrocytes, smooth muscle cells, endothelial cells of blood vessels, pericytes; these cells control whether the vessels are constricted or dilated, which dictates the amount of oxygen and glucose, able to reach the neuronal tissue. Astrocytes are unique in that they are intermediaries that lie between blood neurons, they are able to communicate with other astrocytes via gap junctions and have endfeet that interact with neuronal synapses. These endfeet have the ability to take up various neurotransmitters, such as norepinephrine and glutamate, perform various other functions to maintain chemical and electrical homeostasis in the neuronal environment.
Constriction has been shown in vitro to occur when NE is placed in the synapse and is taken up by astrocyte receptors. NE uptake leads to an increase in intracellular astrocyte Ca2+; when these calcium ion waves spread down the length of the astrocyte, phospholipase A is activated which in turn mobilizes arachidonic acid. These two compounds are transported to the smooth muscle and there react with cytochrome P450 to make 20-hydroxyeicosatetraenoic acid, which acts through yet to-be-determined mechanisms to induce vasoconstriction, it has been shown that agonists of metabotropic glutamate receptors increase intracellular Ca2+ to produce constriction. Dilation occurs when nitric oxide is released from endothelial cells and diffuses into nearby vascular smooth muscle. Several proposed pathways of NO-induced vasodilation have been proposed through haemodynamic investigation, it has been shown that NO inhibits 20-HETE synthesis, which may interfere with astrocytes' constriction pathways and lead to vasodilation.
It has been proposed that NO may amplify astrocyte Ca2+ influx and activate Ca2+-dependent potassium channels, releasing K+ into the interstitial space and inducing hyperpolarization of smooth muscle cells. In addition to this, it has been shown that NO stimulates increased cyclic GMP levels in the smooth muscle cells, inducing a signaling cascade that results in the activation of cGMP-dependent protein kinase and an ultimate decrease in smooth muscle Ca2+ concentration; this leads to a subsequent dilation of the blood vessel. Whether the vessels are constricted or dilated dictates the amount of oxygen and glucose, able to reach the neuronal tissue. A principal function of pericytes is to interact with astrocytes, smooth muscle cells, other intracranial cells to form the blood brain barrier and to modulate the size of blood vessels to ensure proper delivery and distribution of oxygen and nutrients to neuronal tissues. Pericytes have both adrenergic receptors. Stimulation of the latter leads to vessel relaxation, while stimulation of the cholinergic receptors leads to contraction.
Paracrine activity and oxygen availability have been shown to modulate pericyte activity. The peptides are vasoactive. Endothelial cells induce expression of endothelin-1, which leads to NO vasodilation. Experiments have demonstrated that oxygen levels alter pericyte contraction and subsequent blood vessel contraction. In vitro, high oxygen concentrations cause pericyte constriction, while high CO2 concentrations cause relaxation; this suggests that pericytes may have the ability to dilate blood vessels when oxygen is in demand and constrict them when it is in surplus, modifying the rate of blood flow to tissues depending on their metabolic activity. The haemodynamic response is rapid delivery of blood to active neuronal tissue. Complications in this response arise in acute coronary syndromes and pulmonary arterial hypertension; these complications lead to a change in the regulation of blood flow to the brain, in turn the amount of glucose and oxygen, supplied to neurons, which may have serious effects not only on the functioning of the nervous system, but functioning of all bodily systems.
Acute infections, such as community-acquired pneumonia, act as a trigger for acute coronary syndromes. ACS deals with symptoms. Due to this o