Blood clotting mechanisms

Blood platelets are key players in the blood-clotting mechanism. These tiny fragments of cytoplasm are shed into the circulation from the surface of megakaryocytes located in the bone marrow. When the lining of a blood vessel is injured, activated platelets release clotting factors, adhere to each other and to damaged surfaces, and send out numerous filopodia. The shape changes that occur in activated platelets are the result of actin polymerization. Before activation, there are no microfilaments because profilin binds to G-actin and prevents its polymerization. After activation, profilin dissociates from G-actin, and bundles and networks of F-actin filaments rapidly appear within the platelet. 

This sort of control is usually achieved by either covalent modification (phosphorylation or de phosphorylation as in glycogen metabolism) or by proteolytic cleavage (e.g. activation of digestive enzymes in the gut, or blood clotting mechanism. 

Adverse reactions may include the following Fever porphyria dysuria gout hepatic reaction nausea vomiting anorexia thrombocytopenia and sideroblastic anemia with erythroid hyperplasia vacuolation of erythrocytes increased serum iron concentration adverse effects on blood clotting mechanisms mild arthralgia and myalgia hypersensitivity reactions including rashes, urticaria, pruritus fever acne photosensitivity porphyria dysuria interstitial nephritis. 

PRECURSOR. In biological systems, an intermediate compound or molecular complex present in a living organism which, when activated physiochemically, is converted to a specific functional substance. Sometimes the prefix pro is used to indicate that a compound in question plays the role of a precursor. Examples from the history of vitamin and other essential chemical developments include ergosterol (pro-vitamin D2), which is activated by ultraviolet radiation to form vitamin D carotene (provitamin A) is a precursor of vitamin A prothrombin forms thrombin upon activation in the blood-clotting mechanism. 

Laskey, R.A., Honda, B.M., Mills, A.D., Finch, J.T. (1978). Nucleosomes are assembled by an acidic protein which binds histones and transfers them to DNA. Nature (London) 275,416-420. Lederberg, J. Tatum, E.L. (1946). Gene recombination in E. coli. Nature (London) 158, 558. Macfarlane, R.G. (1964). An enzyme cascade in the blood clotting mechanism and its function as a biochemical amplifier. Nature (London) 202,498-499. 

MacFarlane RG, An enzyme cascade in the blood clotting mechanism and its function as a biochemical amplifier. Nature 1964 202 498-499. 

The mode of action of the coumarin anticoagulants involves blocking the regeneration of reduced vitamin K and induces a state of functional vitamin K deficiency, thus interfering with the blood-clotting mechanism (178). 

DEFICIENCY Vitamin K among other things, is important in the blood clotting mechanism. Deficiency results in hemorrhages (especially in newborns—... 

Searcy RL, Simms NM, Foreman JA, Bergquist LM. Evaluation of the blood-clotting mechanism in tetra-cychne-treated patients. Antimicrobial Agents Chemother 1964 10 179-83. 

The ubiquitous occurrence of proteinases is accompanied by a similar distribution of fairly specific proteins that inhibit these enzymes. In normal health, there is a delicate balance between the levels of enzymes and their macromolecular inhibitors. This balance is particularly important in the blood-clotting clot-lysis scheme. Since the total volume of blood in the adult human body is only about 5 1, a massive response is required in the event of an injury that results in a rapid haemorrhage. Some positive feedback is present in the blood-clotting mechanism in order to achieve this rapid response, but clearly this must be sensitively controlled by endogenous inhibitors if a thrombosis is not to occur. 

Vitamins and K2 exist in nature and are essential to the animal for their effect on the blood-clotting mechanism. While 2-methylnaphthoquinone itself and its related derivatives having isoprenoid side chains in position 3 also promote blood coagulation in varying degrees, coenzyme Q10 shows no activity in the blood-coagulating mechanism. Coenzyme Q10, also called ubiquinone because of its ubiquitous occurrence in animal tissues, is important in its own right, since it plays an essential role in oxidative phosphorylation. As in the case of the vitamin K series, the size of the isoprenoid side chain does not appear to be critical with respect to the oxidative phosphorylation activity of the coenzyme Q series. 

McFarlane, R.G., An Enzyme Cascade in the Blood Clotting Mechanism, and its Function as a Biochemical Amplifier. Nature 1964, 202, 498-499. 

Phospholipids are involved in enzyme action, and transport of triglycerides through the liver, in addition they have a role in electron transport and oxidative phosphorylation and in blood-clotting mechanisms. Recent evidence suggests they play a role in the functions of DNA. 

Platelet A short-hved fragment of large cells called megakaryocytes, important component of the blood-clotting mechanism. 

Esnouf, M., Macfarlane, R. Enzymology and the blood clotting mechanism. Advanc. Enzymol. 30, 255-315 (1968)... 

Thrombocyte count and function is normal with the exception of the case of WoHNLiCH (1949), in which the diagnosis of ACD is not certain. A bleeding tendency or specific abnormalities of the blood clotting mechanism have not been reported. Findings from bone marrow biopsies will be reported in the section on pathology (see page 344). 

Ninety-nine per cent of the calcium is in the bones and teeth. The calcium in bones serves not only as a structural component but as a reserve store which can be mobilized for maintenance of serum calcium concentration. The small amount of calcium in serum and in other body fluids has important functions, particularly in neuromuscular excitability and probably also in the blood-clotting mechanism. 

A substance that interferes with one or more of the processes in the blood clotting mechanism. Such agents may be useful in preventing the formation of unwanted clots, and in the breaking up of such clots once they have formed. 

Vitamin K is needed primarily for the blood-clotting mechanism that prevents bleeding to death from cuts and wounds or internal bleeding. Vitamin K is found naturally in plants and can be produced by bacteria in the intestine. The best dietary sources are leafy green vegetables, such as spinach, sprouts, broccoli and cauliflower. Lower levels are found in liver, lean meat, cow milk, egg yolk and whole-wheat products. 

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