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88-451: It has often been described as a gigantic flying snake which produced strange whistling sounds, while its gaze could paralyze an intended victim and permit it to suck its blood . It has often been reported as the cause of blood being sucked from one's sheep. The creature can be eliminated by a machi (Mapuche herbal healer). The name "Piuchén" is also used as the vernacular for the common vampire bat species Desmodus rotundus , which can be

176-531: A blood component whose function (along with the coagulation factors ) is to react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot . Platelets have no cell nucleus ; they are fragments of cytoplasm derived from the megakaryocytes of the bone marrow or lung, which then enter the circulation. Platelets are found only in mammals, whereas in other vertebrates (e.g. birds , amphibians ), thrombocytes circulate as intact mononuclear cells . One major function of platelets

264-731: A blood bank . There are many different blood types in humans, the ABO blood group system , and the Rhesus blood group system being the most important. Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, so crossmatching is done to ensure that a compatible blood product is transfused. Other blood products administered intravenously are platelets, blood plasma, cryoprecipitate, and specific coagulation factor concentrates. Many forms of medication (from antibiotics to chemotherapy ) are administered intravenously, as they are not readily or adequately absorbed by

352-574: A blood transfusion, because the metabolism of transfused red blood cells does not restart immediately after a transfusion. In modern evidence-based medicine , bloodletting is used in management of a few rare diseases, including hemochromatosis and polycythemia . However, bloodletting and leeching were common unvalidated interventions used until the 19th century, as many diseases were incorrectly thought to be due to an excess of blood, according to Hippocratic medicine. English blood ( Old English blod ) derives from Germanic and has cognates with

440-701: A multitude of microthrombi of similar composition to that in physiological immunothrombosis — fibrin, platelets, neutrophils and NETs. Platelets rapidly deploy to sites of injury or infection, and potentially modulate inflammatory processes by interacting with leukocytes and secreting cytokines , chemokines , and other inflammatory mediators. Platelets also secrete platelet-derived growth factor (PDGF). Platelets modulate neutrophils by forming platelet-leukocyte aggregates (PLAs). These formations induce upregulated production of αmβ2 ( Mac-1 ) integrin in neutrophils. Interaction with PLAs also induces degranulation and increased phagocytosis in neutrophils. Platelets are

528-426: A pH below 7.35 is too acidic , whereas blood pH above 7.45 is too basic. A pH below 6.9 or above 7.8 is usually lethal. Blood pH, partial pressure of oxygen (pO 2 ) , partial pressure of carbon dioxide (pCO 2 ) , and bicarbonate (HCO 3 ) are carefully regulated by a number of homeostatic mechanisms , which exert their influence principally through the respiratory system and the urinary system to control

616-676: A receptor for IgG's constant fragment (Fc). When activated and bound to IgG opsonised bacteria, platelets release reactive oxygen species (ROS), antimicrobial peptides, defensins , kinocidins and proteases , killing the bacteria directly. Platelets also secrete proinflammatory and procoagulant mediators such as inorganic polyphosphates or platelet factor 4 (PF4), connecting innate and adaptive immune responses. Spontaneous and excessive bleeding can occur because of platelet disorders. This bleeding can be caused by deficient numbers of platelets, dysfunctional platelets, or platelet densities over 1 million/microliter. (The excessive numbers create

704-777: A relative von Willebrand factor deficiency due to sequestration.) Bleeding due to a platelet disorder or a coagulation factor disorder can be distinguished by the characteristics and location of the bleeding. Platelet bleeding involves bleeding from a cut is prompt and excessive, but can be controlled by pressure; spontaneous bleeding into the skin which causes a purplish stain named by its size: petechiae , purpura , ecchymoses ; bleeding into mucous membranes causing bleeding gums, nose bleed, and gastrointestinal bleeding; menorrhagia; and intraretinal and intracranial bleeding. Excessive numbers of platelets, and/or normal platelets responding to abnormal vessel walls, can result in venous thrombosis and arterial thrombosis . The symptoms depend on

792-494: A result of turning on the GPIIb/IIIa receptor, allowing these receptors to bind with vWF or fibrinogen . Each platelet has around 60,000 of these receptors. When any one or more of at least nine different platelet surface receptors are turned on during activation, intraplatelet signaling pathways cause existing GpIIb/IIIa receptors to change shape — curled to straight — and thus become capable of binding. Since fibrinogen

880-549: A similar range of meanings in all other Germanic languages (e.g. German Blut , Swedish blod , Gothic blōþ ). There is no accepted Indo-European etymology. Robin Fåhræus (a Swedish physician who devised the erythrocyte sedimentation rate ) suggested that the Ancient Greek system of humorism , wherein the body was thought to contain four distinct bodily fluids (associated with different temperaments), were based upon

968-428: A sixth step, wound repair . Platelets participate in both innate and adaptive intravascular immune responses. In addition to facilitating the clotting process, platelets contain cytokines and growth factors which can promote wound healing and regeneration of damaged tissues. The term thrombocyte (clot cell) came into use in the early 1900s and is sometimes used as a synonym for platelet; but not generally in

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1056-423: Is blood plasma , a fluid that is the blood's liquid medium, which by itself is straw-yellow in color. The blood plasma volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human. It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins , and trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose , amino acids , and fatty acids (dissolved in

1144-449: Is a rod-like protein with nodules on either end capable of binding GPIIb/IIIa, activated platelets with exposed GPIIb/IIIa can bind fibrinogen to aggregate. GPIIb/IIIa may also further anchor the platelets to subendothelial vWF for additional structural stabilisation. Classically it was thought that this was the only mechanism involved in aggregation, but three other mechanisms have been identified which can initiate aggregation, depending on

1232-585: Is a system for analysing platelet function in which citrated whole blood is aspirated through a disposable cartridge containing an aperture within a membrane coated with either collagen and epinephrine or collagen and ADP. These agonists induce platelet adhesion, activation and aggregation, leading to rapid occlusion of the aperture and cessation of blood flow termed the closure time (CT). An elevated CT with EPI and collagen can indicate intrinsic defects such as von Willebrand disease , uremia , or circulating platelet inhibitors. A follow-up test involving collagen and ADP

1320-596: Is also stored in the Weibel-Palade bodies of the endothelial cells and secreted constitutively into the blood. Platelets store vWF in their alpha granules. When the endothelial layer is disrupted, collagen and VWF anchor platelets to the subendothelium. Platelet GP1b-IX-V receptor binds with VWF; and GPVI receptor and integrin α2β1 bind with collagen. The intact endothelial lining inhibits platelet activation by producing nitric oxide , endothelial- ADPase , and PGI 2 (prostacyclin). Endothelial-ADPase degrades

1408-461: Is arterial or venous blood). Most of it (about 70%) is converted to bicarbonate ions HCO − 3 by the enzyme carbonic anhydrase in the red blood cells by the reaction CO 2 + H 2 O → H 2 CO 3 → H + HCO − 3 ; about 7% is dissolved in the plasma; and about 23% is bound to hemoglobin as carbamino compounds. Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However,

1496-418: Is associated with a large number of beliefs. One of the most basic is the use of blood as a symbol for family relationships through birth/parentage; to be "related by blood" is to be related by ancestry or descendence, rather than marriage. This bears closely to bloodlines , and sayings such as " blood is thicker than water " and " bad blood ", as well as " Blood brother ". Blood is given particular emphasis in

1584-403: Is associated with activation of the coagulation cascade , with resultant fibrin deposition and linking (secondary hemostasis). These processes may overlap: the spectrum is from a predominantly platelet plug, or "white clot" to a predominantly fibrin, or "red clot" or the more typical mixture. Berridge adds retraction and platelet inhibition as fourth and fifth steps, while others would add

1672-440: Is bright red, because carbon monoxide causes the formation of carboxyhemoglobin . In cyanide poisoning, the body cannot use oxygen, so the venous blood remains oxygenated, increasing the redness. There are some conditions affecting the heme groups present in hemoglobin that can make the skin appear blue – a symptom called cyanosis . If the heme is oxidized, methemoglobin , which is more brownish and cannot transport oxygen,

1760-407: Is circulated around the body through blood vessels by the pumping action of the heart . In humans, blood is pumped from the strong left ventricle of the heart through arteries to peripheral tissues and returns to the right atrium of the heart through veins . It then enters the right ventricle and is pumped through the pulmonary artery to the lungs and returns to the left atrium through

1848-480: Is dangerous to health, and severe hypoxia (saturations less than 30%) may be rapidly fatal. A fetus , receiving oxygen via the placenta , is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), so fetuses produce another form of hemoglobin with a much higher affinity for oxygen ( hemoglobin F ) to function under these conditions. CO 2 is carried in blood in three different ways. (The exact percentages vary depending whether it

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1936-426: Is formed. In the rare condition sulfhemoglobinemia , arterial hemoglobin is partially oxygenated, and appears dark red with a bluish hue. Veins close to the surface of the skin appear blue for a variety of reasons. However, the factors that contribute to this alteration of color perception are related to the light-scattering properties of the skin and the processing of visual input by the visual cortex , rather than

2024-436: Is free to bind oxygen, and fewer oxygen molecules can be transported throughout the blood. This can cause suffocation insidiously. A fire burning in an enclosed room with poor ventilation presents a very dangerous hazard, since it can create a build-up of carbon monoxide in the air. Some carbon monoxide binds to hemoglobin when smoking tobacco. Blood for transfusion is obtained from human donors by blood donation and stored in

2112-461: Is in equilibrium with lymph , which is continuously formed in tissues from blood by capillary ultrafiltration. Lymph is collected by a system of small lymphatic vessels and directed to the thoracic duct , which drains into the left subclavian vein , where lymph rejoins the systemic blood circulation. Blood circulation transports heat throughout the body, and adjustments to this flow are an important part of thermoregulation . Increasing blood flow to

2200-444: Is initiated either by immune cells by activating their pattern recognition receptors (PRRs), or by platelet-bacterial binding. Platelets can bind to bacteria either directly through thrombocytic PRRs and bacterial surface proteins, or via plasma proteins that bind both to platelets and bacteria. Monocytes respond to bacterial pathogen-associated molecular patterns (PAMPs), or damage-associated molecular patterns (DAMPs) by activating

2288-570: Is known as the Haldane effect , and is important in the transport of carbon dioxide from the tissues to the lungs. A rise in the partial pressure of CO 2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the Bohr effect . Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin binds most of the hydrogen ions as it has a much greater affinity for more hydrogen than does oxyhemoglobin. In mammals, blood

2376-436: Is mixed with saline and a platelet agonist in a single-use cuvette with two pairs of electrodes. The increase in impedance between the electrodes as platelets aggregate onto them, is measured and visualized as a curve. In light transmission aggregometry (LTA), platelet-rich plasma is placed between a light source and a photocell . Unaggregated plasma allows relatively little light to pass through. After adding an agonist,

2464-515: Is oxygenated and dark red when it is deoxygenated . Medical terms related to blood often begin with hemo- , hemato- , haemo- or haemato- from the Greek word αἷμα ( haima ) 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

2552-493: Is produced predominantly by the liver , while hormones are produced by the endocrine glands and the watery fraction is regulated by the hypothalamus and maintained by the kidney . Healthy erythrocytes have a plasma life of about 120 days before they are degraded by the spleen , and the Kupffer cells in the liver. The liver also clears some proteins, lipids, and amino acids. The kidney actively secretes waste products into

2640-442: Is the chemical motor that pulls the invaginated OCS out of the interior of the platelet, like turning pants pockets inside out, creating the dendrites. This process is similar to the mechanism of contraction in a muscle cell . The entire OCS thus becomes indistinguishable from the initial platelet membrane as it forms the "fried egg". This dramatic increase in surface area comes about with neither stretching nor adding phospholipids to

2728-463: Is the process. Structurally the platelet can be divided into four zones, from peripheral to innermost: Circulating inactivated platelets are biconvex discoid (lens-shaped) structures, 2–3 μm in greatest diameter. Activated platelets have cell membrane projections covering their surface. In a first approximation, the shape can be considered similar to oblate spheroids , with a semiaxis ratio of 2 to 8. This approximation can be used to model

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2816-464: Is to clump together to stop acute bleeding. This process is complex, as more than 193 proteins and 301 interactions are involved in platelet dynamics. Despite much overlap, platelet function can be modeled in three steps: Thrombus formation on an intact endothelium is prevented by nitric oxide , prostacyclin , and CD39 . Endothelial cells attach to the subendothelial collagen by von Willebrand factor (VWF), which these cells produce. VWF

2904-520: Is to contribute to hemostasis : the process of stopping bleeding at the site of interrupted endothelium . They gather at the site and, unless the interruption is physically too large, they plug the hole. First, platelets attach to substances outside the interrupted endothelium: adhesion . Second, they change shape, turn on receptors and secrete chemical messengers : activation . Third, they connect to each other through receptor bridges: aggregation . Formation of this platelet plug (primary hemostasis)

2992-450: Is used to indicate if the abnormal CT with collagen and EPI was caused by the effects of acetyl sulfosalicylic acid (aspirin) or medications containing inhibitors. The PFA-100 is highly sensitive to von Willebrand disease, but is only moderately sensitive to defects in platelet function. Low platelet concentration is called thrombocytopenia , and is due to either decreased production or increased destruction. Elevated platelet concentration

3080-561: The Islamic , Jewish , and Christian religions, because Leviticus 17:11 says "the life of a creature is in the blood." This phrase is part of the Levitical law forbidding the drinking of blood or eating meat with the blood still intact instead of being poured off. Platelet Platelets or thrombocytes (from Ancient Greek θρόμβος ( thrómbos )  'clot' and κύτος ( kútos )  'cell') are

3168-520: The PI3K/Akt pathway during a first wave of aggregation, leading to thrombin generation and PAR‐1 activation, which evokes a second wave of aggregation. Platelet activation begins seconds after adhesion occurs. It is triggered when collagen from the subendothelium binds with its receptors ( GPVI receptor and integrin α2β1) on the platelet. GPVI is associated with the Fc receptor gamma chain and leads via

3256-529: The acid–base balance and respiration, which is called compensation. An arterial blood gas test measures these. Plasma also circulates hormones transmitting their messages to various tissues. The list of normal reference ranges for various blood electrolytes is extensive. Human blood is typical of that of mammals, although the precise details concerning cell numbers, size, protein structure , and so on, vary somewhat between species. In non-mammalian vertebrates, however, there are some key differences: Blood

3344-912: The circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells , and transports metabolic waste products away from those same cells. Blood is composed of blood cells suspended in blood plasma . Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains proteins , glucose , mineral ions , and hormones . The blood cells are mainly red blood cells (erythrocytes), white blood cells (leukocytes), and (in mammals) platelets (thrombocytes). The most abundant cells are red blood cells. These contain hemoglobin , which facilitates oxygen transport by reversibly binding to it, increasing its solubility. Jawed vertebrates have an adaptive immune system , based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in

3432-405: The clotting of blood. 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, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Blood is bright red when its hemoglobin

3520-428: The erectile tissue in the penis and clitoris . Another example of a hydraulic function is the jumping spider , in which blood forced into the legs under pressure causes them to straighten for a powerful jump, without the need for bulky muscular legs. Hemoglobin is the principal determinant of the color of blood ( hemochrome ). Each molecule has four heme groups, and their interaction with various molecules alters

3608-482: The pulmonary veins . Blood then enters the left ventricle to be circulated again. Arterial blood carries oxygen from inhaled air to all of the cells of the body, and venous blood carries carbon dioxide, a waste product of metabolism by cells , to the lungs to be exhaled. However, one exception includes pulmonary arteries, which contain the most deoxygenated blood in the body, while the pulmonary veins contain oxygenated blood. Additional return flow may be generated by

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3696-479: The urine . About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the hemoglobin . About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species. Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O 2 per gram hemoglobin, which increases

3784-516: The CO 2 bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of allosteric effects on the hemoglobin molecule, the binding of CO 2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels

3872-767: The NETosis and phagocytosis. Platelets also participate in chronic inflammatory disease, such as synovitis or rheumatoid arthritis . Platelets are activated by collagen receptor glycoprotein IV (GPVI). Proinflammatory platelet microvesicles trigger constant cytokine secretion from neighboring fibroblast-like synoviocytes , most prominently Il-6 and Il-8 . Inflammatory damage to the surrounding extracellular matrix continuously reveals more collagen, maintaining microvesicle production. Activated platelets are able to participate in adaptive immunity , interacting with antibodies . They are able to specifically bind IgG through FcγRIIA ,

3960-436: The activation of a tyrosine kinase cascade finally to the activation of PLC-gamma2 ( PLCG2 ) and more calcium release. Tissue factor also binds to factor VII in the blood, which initiates the extrinsic coagulation cascade to increase thrombin production. Thrombin is a potent platelet activator, acting through Gq and G12. These are G protein-coupled receptors and they turn on calcium-mediated signaling pathways within

4048-483: The actual color of the venous blood. Skinks in the genus Prasinohaema have green blood due to a buildup of the waste product biliverdin . Substances other than oxygen can bind to hemoglobin; in some cases, this can cause irreversible damage to the body. Carbon monoxide, for example, is extremely dangerous when carried to the blood via the lungs by inhalation, because carbon monoxide irreversibly binds to hemoglobin to form carboxyhemoglobin, so that less hemoglobin

4136-426: The bacteria. Although thrombosis, blood coagulation in intact blood vessels, is usually viewed as a pathological immune response, leading to obturation of lumen of blood vessel and subsequent hypoxic tissue damage, in some cases, directed thrombosis, called immunothrombosis, can locally control the spread of an infection. The thrombosis is directed in concordance of platelets, neutrophils and monocytes . The process

4224-445: The binding of these coagulation factors. In addition to interacting with vWF and fibrin, platelets interact with thrombin, Factors X, Va, VIIa, XI, IX, and prothrombin to complete formation via the coagulation cascade. Human platelets do not express tissue factor . Rat platelets do express tissue factor protein and carry both tissue factor pre-mRNA and mature mRNA. Platelet aggregation begins minutes after activation, and occurs as

4312-473: The blood or bound to plasma proteins), and removes waste products, such as carbon dioxide , urea , and lactic acid . Other important components include: The term serum refers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin and immunoglobulins . Blood pH is regulated to stay within the narrow range of 7.35 to 7.45, making it slightly basic (compensation). Extra-cellular fluid in blood that has

4400-475: The body, including: Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m , very close to pure water's density of 1000 kg/m . The average adult has a blood volume of roughly 5 litres (11 US pt) or 1.3 gallons, which is composed of plasma and formed elements . The formed elements are the two types of blood cell or corpuscle – the red blood cells , (erythrocytes) and white blood cells (leukocytes), and

4488-422: The cell fragments called platelets that are involved in clotting. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%. Whole blood (plasma and cells) exhibits non-Newtonian fluid dynamics . One microliter of blood contains: 45 ± 7 (38–52%) for males 42 ± 5 (37–47%) for females Oxygenated: 98–99% Deoxygenated: 75% About 55% of blood

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4576-429: The connection between thrombocytes and immune cells. The platelet cell membrane has receptors for collagen. Following rupture of the blood vessel wall, platelets are exposed and adhere to the collagen in the surrounding tissue. As hemostasis is a basic function of thrombocytes in mammals, it also has its uses in possible infection confinement. In case of injury, platelets, together with the coagulation cascade, provide

4664-489: The coupled Gs protein to increase adenylate cyclase activity and increases the production of cAMP, further promoting the efflux of calcium and reducing intracellular calcium availability for platelet activation. ADP on the other hand binds to purinergic receptors on the platelet surface. Since the thrombocytic purinergic receptor P2Y12 is coupled to Gi proteins, ADP reduces platelet adenylate cyclase activity and cAMP production, leading to accumulation of calcium inside

4752-413: The digestive tract. After severe acute blood loss, liquid preparations, generically known as plasma expanders, can be given intravenously, either solutions of salts (NaCl, KCl, CaCl 2 etc.) at physiological concentrations, or colloidal solutions, such as dextrans, human serum albumin , or fresh frozen plasma. In these emergency situations, a plasma expander is a more effective life-saving procedure than

4840-431: The exact color. Arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group. Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen during blood donation and when venous blood samples are taken. This is because the spectrum of light absorbed by hemoglobin differs between the oxygenated and deoxygenated states. Blood in carbon monoxide poisoning

4928-483: The exterior. Bound and activated platelets degranulate to release platelet chemotactic agents to attract more platelets to the site of endothelial injury. Granule characteristics: As shown by flow cytometry and electron microscopy , the most sensitive sign of activation, when exposed to platelets using ADP, are morphological changes. Mitochondrial hyperpolarization is a key event in initiating morphology changes. Intraplatelet calcium concentration increases, stimulating

5016-455: The extrinsic pathway of coagulation. Neutrophils facilitate the blood coagulation by NETosis , while platelets facilitate neutrophils' NETosis. NETs bind tissue factor, binding the coagulation centers to the location of infection. They also activate the intrinsic coagulation pathway by providing its negatively charged surface to the factor XII. Other neutrophil secretions, such as proteolytic enzymes which cleave coagulation inhibitors, also bolster

5104-552: The first line of defense by forming a blood clot. Hemostasis and host defense were thus intertwined in evolution. For example, in the Atlantic horseshoe crab (estimated to be over 400 million years old), the only blood cell type, the amebocyte , facilitates both the hemostatic function and the encapsulation and phagocytosis of pathogens by means of exocytosis of intracellular granules containing bactericidal defense molecules. Blood clotting supports immune function by trapping

5192-400: The hydrodynamic and optical properties of a population, as well as to restore the geometric parameters of individual measured platelets by flow cytometry . More accurate biophysical models of platelet surface morphology that model its shape from first principles, make it possible to obtain a more realistic platelet geometry in a calm and activated state. The fundamental function of platelets

5280-433: The interplay between the microtubule/actin filament complex. The continuous changes in shape from the unactivated to the fully activated platelet are best seen via scanning electron microscopy . The three steps along this path are named early dendritic , early spread, and spread . The surface of the unactivated platelet looks similar to the surface of the brain–a wrinkled appearance from numerous shallow folds that increase

5368-455: The largest source of soluble CD40L which induces production of reactive oxygen species (ROS) and upregulate expression of adhesion molecules, such as E-selectin , ICAM-1 , and VCAM-1 , in neutrophils, activates macrophages and activates cytotoxic response in T and B lymphocytes . Mammalian platelets lacking nucleus are able to conduct autonomous locomotion. Platelets are active scavengers, scaling walls of blood vessels and reorganising

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5456-530: The lungs is still roughly 75% (70 to 78%) saturated. Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions. Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia). Sustained hypoxia (oxygenation less than 90%),

5544-407: The movement of skeletal muscles , which can compress veins and push blood through the valves in veins toward the right atrium . The blood circulation was famously described by William Harvey in 1628. In vertebrates, the various cells of blood are made in the bone marrow in a process called hematopoiesis , which includes erythropoiesis , the production of red blood cells; and myelopoiesis ,

5632-464: The observation of blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile"). In general, Greek thinkers believed that blood

5720-410: The origin of the legend. This article relating to a myth or legend from Argentina is a stub . You can help Misplaced Pages by expanding it . This article relating to a myth or legend from Chile is a stub . You can help Misplaced Pages by expanding it . This article about a legendary creature is a stub . You can help Misplaced Pages by expanding it . Blood Blood is a body fluid in

5808-433: The other to form the final fibrin-crosslinked thrombus. Collagen-mediated GPVI signalling increases the platelet production of thromboxane A2 (TXA2) and decreases the production of prostacyclin . This occurs by altering the metabolic flux of platelet's eicosanoid synthesis pathway, which involves enzymes phospholipase A2 , cyclo-oxygenase 1 , and thromboxane-A synthase . Platelets secrete thromboxane A2, which acts on

5896-419: The oxygen is consumed; afterwards, venules and veins carry deoxygenated blood back to the heart. Under normal conditions in adult humans at rest, hemoglobin in blood leaving the lungs is about 98–99% saturated with oxygen , achieving an oxygen delivery between 950 and 1150 ml/min to the body. In a healthy adult at rest, oxygen consumption is approximately 200–250 ml/min, and deoxygenated blood returning to

5984-413: The platelet activator ADP . Resting platelets maintain active calcium efflux via a cyclic AMP -activated calcium pump. Intracellular calcium concentration determines platelet activation status, as it is the second messenger that drives platelet conformational change and degranulation. Endothelial prostacyclin binds to prostanoid receptors on the surface of resting platelets. This event stimulates

6072-504: The platelet by inactivating the cAMP calcium efflux pump. The other ADP-receptor P2Y1 couples to Gq that activates phospholipase C-beta 2 ( PLCB2 ), resulting in inositol 1,4,5-trisphosphate (IP3) generation and intracellular release of more calcium. This together induces platelet activation. Endothelial ADPase degrades ADP and prevents this from happening. Clopidogrel and related antiplatelet medications also work as purinergic receptor P2Y12 antagonists . Data suggest that ADP activates

6160-441: The platelet membrane. Platelet activation causes its membrane surface to become negatively charged. One of the signaling pathways turns on scramblase , which moves negatively charged phospholipids from the inner to the outer platelet membrane surface. These phospholipids then bind the tenase and prothrombinase complexes, two of the sites of interplay between platelets and the coagulation cascade. Calcium ions are essential for

6248-447: The platelet's own thromboxane receptors on the platelet surface (hence the so-called "out-in" mechanism), and those of other platelets. These receptors trigger intraplatelet signaling, which converts GPIIb/IIIa receptors to their active form to initiate aggregation . Platelets contain dense granules , lambda granules, and alpha granules . Activated platelets secrete the contents of these granules through their canalicular systems to

6336-406: The platelet, overcoming the baseline calcium efflux. Families of three G proteins (Gq, Gi, G12) operate together for full activation. Thrombin also promotes secondary fibrin-reinforcement of the platelet plug. Platelet activation in turn degranulates and releases factor V and fibrinogen , potentiating the coagulation cascade. Platelet plugging and coagulation occur simultaneously, with each inducing

6424-409: The platelets aggregate, increasing light transmission, which is detected by a photocell. Whole blood impedance aggregometry (WBA) measures the change in electrical impedance between two electrodes when platelet aggregation is induced by an agonist. Whole blood lumiaggregometry may increase the test sensitivity to impairment of platelet granule secretion. The PFA-100 (Platelet Function Assay — 100)

6512-501: The population average between 250,000 and 260,000 cells per mm (equivalent to per microliter), but the typical laboratory accepted normal range is between 150,000 and 400,000 cells per mm or 150–400 × 10 per liter. On a stained blood smear , platelets appear as dark purple spots, about 20% of the diameter of red blood cells. The smear reveals size, shape, qualitative number, and clumping . A healthy adult typically has 10 to 20 times more red blood cells than platelets. Bleeding time

6600-452: The process. In case of imbalance throughout the regulation of immunothrombosis, this process can become aberrant. Regulatory defects in immunothrombosis are suspected to be a major factor in pathological thrombosis in forms such as disseminated intravascular coagulation (DIC) or deep vein thrombosis . DIC in sepsis is a prime example of both the dysregulated coagulation process as well as an undue systemic inflammatory response, resulting in

6688-505: The production of white blood cells and platelets. During childhood, almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs. In addition, during childhood, the thymus gland, found in the mediastinum , is an important source of T lymphocytes . The proteinaceous component of blood (including clotting proteins)

6776-406: The scientific literature, except as a root word for other terms related to platelets (e.g. thrombocytopenia meaning low platelets). The term thrombocytes are proper for mononuclear cells found in the blood of non-mammalian vertebrates: they are the functional equivalent of platelets, but circulate as intact cells rather than cytoplasmic fragments of bone marrow megakaryocytes. In some contexts,

6864-422: The second and the third most supplied organs, with 1100 ml/min and ~700 ml/min, respectively. Relative rates of blood flow per 100 g of tissue are different, with kidney, adrenal gland and thyroid being the first, second and third most supplied tissues, respectively. The restriction of blood flow can also be used in specialized tissues to cause engorgement, resulting in an erection of that tissue; examples are

6952-489: The surface (e.g., during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss. In contrast, when the external temperature is low, blood flow to the extremities and surface of the skin is reduced and to prevent heat loss and is circulated to the important organs of the body, preferentially. Rate of blood flow varies greatly between different organs. Liver has the most abundant blood supply with an approximate flow of 1350 ml/min. Kidney and brain are

7040-487: The surface area; early dendritic , an octopus with multiple arms and legs; early spread , an uncooked frying egg in a pan, the "yolk" is the central body; and the spread , a cooked fried egg with a denser central body. These changes are all brought about by the interaction of the microtubule/actin complex with the platelet cell membrane and open canalicular system (OCS), which is an extension and invagination of that membrane. This complex runs just beneath these membranes and

7128-440: The thrombosis site. Platelet concentration in the blood (i.e. platelet count), can be measured manually using a hemocytometer , or by placing blood in an automated platelet analyzer using particle counting, such as a Coulter counter or optical methods. Most common blood testing methods include platelet count in their measurements, usually reported as PLT . Platelet concentrations vary between individuals and over time, with

7216-409: The thrombus. They are able to recognize and adhere to many surfaces, including bacteria, and can envelop them in their open canalicular system (OCP), leading to a proposal to name the process as covercytosis (OCS) rather than phagocytosis, as OCS is merely an invagination of outer plasma membrane. These platelet-bacteria bundles provide an interaction platform for neutrophils that destroy bacteria using

7304-443: The total blood oxygen capacity seventyfold, compared to if oxygen solely were carried by its solubility of 0.03 ml O 2 per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries). With the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries , where

7392-493: The velocity of blood flow (i.e. shear range). Platelets have a central role in innate immunity , initiating and participating in multiple inflammatory processes, directly binding and even destroying pathogens. Clinical data show that many patients with serious bacterial or viral infections have thrombocytopenia , thus reducing their contribution to inflammation. Platelet-leukocyte aggregates (PLAs) found in circulation are typical in sepsis or inflammatory bowel disease , showing

7480-419: The word thrombus is used interchangeably with the word clot , regardless of its composition (white, red, or mixed). In other contexts it is used to contrast a normal from an abnormal clot: thrombus arises from physiologic hemostasis, thrombosis arises from a pathologic and excessive quantity of clot. In a third context it is used to contrast the result from the process: thrombus is the result, thrombosis

7568-442: Was developed as a test of platelet function by Duke in 1910. Duke's test measured the time taken for bleeding to stop from a standardized wound in the ear lobe that was blotted every 30 seconds, considering less than 3 minutes as normal. Bleeding time has low sensitivity and specificity for mild to moderate platelet disorders and is no longer recommended for screening. In multiple electrode aggregometry , anticoagulated whole blood

7656-492: Was discovered in the year 1900 by Karl Landsteiner . Jan Janský is credited with the first classification of blood into the four types (A, B, AB, and O) in 1907, which remains in use today. In 1907 the first blood transfusion was performed that used the ABO system to predict compatibility. The first non-direct transfusion was performed on 27 March 1914. The Rhesus factor was discovered in 1937. Due to its importance to life, blood

7744-464: Was made from food. Plato and Aristotle are two important sources of evidence for this view, but it dates back to Homer's Iliad . Plato thinks that fire in our bellies transform food into blood. Plato believes that the movements of air in the body as we exhale and inhale carry the fire as it transforms our food into blood. Aristotle believed that food is concocted into blood in the heart and transformed into our body's matter. The ABO blood group system

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