血小板

Platelets

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.

或稱凝血細胞，為一盤狀結構，直徑2 - 4 µm，哺乳動物血液成分之一，具有重要的血液凝固作用，無核，無DNA，但含活性酶和線粒體。為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損表面，血小板數(shù)為平均每立方米250000，由紅骨髓細胞中巨核細胞斷裂而成。血小板生成由血小板生成素和調節(jié)性淋巴細胞控制。有1/3血小板在脾臟，其余2/3存在于循環(huán)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.

血小板的作用與血液凝固有關。血小板具有粘附和凝集力，因此，它能夠閉合血管中的小傷口，阻止出血。血小板粘附在受損血管的膠原上，快速釋放ADP，進而激發(fā)血栓烷A2的合成。血栓烷A2是一種很有效的前列腺素，可促成血小板凝集和局部血管收縮。并釋放出也血小板膜相關的纖維蛋白原、V和VIII因子、鈣離子和血小板磷脂（PF-3)。并通過凝集血小板釋放其他物質，如血小板球蛋白、PF-4有絲分裂因子（如血小板衍生的生長因子)、凝血酶敏感素、ADP、血清素鈣離子等。醫(yī).學全.在.線網(wǎng)站52667788.cn

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.

血小板增多提示脫水或生成細胞的骨髓的刺激，血小板減少可能表明免疫系統(tǒng)衰竭、藥物反應、B12或葉酸缺乏。血小板數(shù)量減少可致病人易于出血，有時甚至是無損傷性出血。造成低血小板計數(shù)的原因包括自身免疫疾病、化療、白血病、病毒感染及藥物。

Platelet Ranges

血小板范圍

Normal Adult Range: 130 - 400 thous/mcl

成人正常：130-400 ×109 /L

Optimal Adult Reading: 265×109

成人最佳：265×109

Higher ranges are found in children, newborns and infants.

兒童、新生兒及嬰兒血小板計數(shù)較高。