血小板

　　Or thrombocyte; a disk-shaped structure, 2 to 4 µm in diameter, found in the blood of mammals and important for its role in blood coagulation; platelets lack a nucleus and DNA but contain active enzymes and mitochondria. They are the smallest of the formed elements in blood with a very fragile membrane; they tend to adhere to uneven or damaged surfaces. They average about 250,000 per cubic millimeter of blood and are formed in the red bone marrow by fragmentation of megakaryocytes. Platelet production is controlled by a hormone, thrombopoietin, and regulatory lymphocytes. At any given time about one-third of the total blood platelets can be found in the spleen; the remaining two-thirds are in the circulating blood.

　　或称凝血细胞，为一盘状结构，直径2 - 4 µm，哺乳动物血液成分之一，具有重要的血液凝固作用，无核，无DNA，但含活性酶和线粒体。为血液中最小的有形成分，粘膜易碎。血小板易于粘附在凹凸不平或破损表面，血小板数为平均每立方米250000，由红骨髓细胞中巨核细胞断裂而成。血小板生成由血小板生成素和调节性淋巴细胞控制。有1/3血小板在脾脏，其余2/3存在于循环血液中。

　　The functions of platelets are related to the clotting of blood. Because of their adhesion and aggregation capabilities platelets can occlude small breaks in blood vessels and prevent the escape of blood. Platelets which have adhered to exposed collagen in damaged vessels release ADP in milliseconds which in turn initiates the synthesis of thromboxane A2, a very potent prostaglandin which causes platelet aggregation and localized vasoconstriction. Fibrinogen, factors V and VIII, calcium ions, platelet phospholipid (PF-3), associated with the platelet membrane are also released. Substances contained within the platelet granules such as thromboglobulin, heparin neutralizing activity (PF-4) mitogens such as platelet derived growth factor, thrombospondin, ADP, serotonin and calcium ions are also released by aggregated platelets.（form www.med66.com ）

　　血小板的作用与血液凝固有关。血小板具有粘附和凝集力，因此，它能够闭合血管中的小伤口，阻止出血。血小板粘附在受损血管的胶原上，快速释放ADP，进而激发血栓烷A2的合成。血栓烷A2是一种很有效的前列腺素，可促成血小板凝集和局部血管收缩。并释放出也血小板膜相关的纤维蛋白原、V和VIII因子、钙离子和血小板磷脂（PF-3）。并通过凝集血小板释放其他物质，如血小板球蛋白、PF-4有丝分裂因子（如血小板衍生的生长因子）、凝血酶敏感素、ADP、血清素钙离子等。

　　Elevated levels suggest dehydration or stimulation of the bone marrow where the cells are produced and decreased levels may indicate an immune system failure, drug reactions, B12 or folic acid deficiency. Low numbers of platelets can make a person vulnerable to bleeding, sometimes even without injury occurring. Causes of low platelet counts include autoimmune diseases, chemotherapy, leukaemia, viral infections and some medicines.

　　血小板增多提示脱水或生成细胞的骨髓的刺激，血小板减少可能表明免疫系统衰竭、药物反应、B12或叶酸缺乏。血小板数量减少可致病人易于出血，有时甚至是无损伤性出血。造成低血小板计数的原因包括自身免疫疾病、化疗、白血病、病毒感染及药物。 医 学教 育网

　　Platelet Ranges

　　血小板范围

　　Normal Adult Range: 130 - 400 thous/mcl

　　成人正常：130-400 ×109 /L

　　Optimal Adult Reading: 265×109

　　成人最优：265×109

　　Higher ranges are found in children, newborns and infants.

　　儿童、新生儿及婴儿血小板计数较高。