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Platelets derive from multipotent marrow stem cells. Megakaryocyte and platelet production is regulated by thrombopoietin, a hormone produced in the kidneys and liver. Each megakaryocyte produces between 1,000 and 3,000 platelets during its lifetime. An average of 10 11 platelets are produced daily in a healthy adult.
In a typical set of rules, a platelet donor must weigh at least 50 kg (110 lb) and have a platelet count of at least 150 x 10 9 /L (150,000 platelets per mm³). [2] One unit has greater than 3×10 11 platelets. Therefore, it takes 2 liters of blood having a platelet count of 150,000/mm³ to produce one unit of platelets.
They circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots. Platelets release thread-like fibers to form these clots. The normal range (99% of population analyzed) for platelets is 150,000 to 450,000 per cubic millimeter. [6] If the number of platelets is too low, excessive bleeding can occur.
The blood cells are mainly red blood cells (erythrocytes), white blood cells (leukocytes), and (in mammals) platelets (thrombocytes). [3] The most abundant cells are red blood cells. [4] These contain hemoglobin, which facilitates oxygen transport by reversibly binding to it, increasing its solubility. [5]
Low levels of platelets in turn may lead to prolonged or excessive bleeding. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients and a third of surgical patients. [3] A normal human platelet count ranges from 150,000 to 450,000 platelets/microliter (μL) of blood. [4]
Platelets are regulators of hemostasis and thrombosis. Platelets become active in the blood following vascular injury. Vascular injury causes platelets to stick to the cellular matrix that is exposed under the endothelium, form a platelet plug, and then form a thrombus. Platelets are essential in the formation of an occlusive thrombus and are ...
High platelet counts can occur in patients with polycythemia vera (high red blood cell counts), and is an additional risk factor for complications. [ citation needed ] A very small number of people report symptoms of erythromelalgia , a burning sensation and redness of the extremities that resolves with cooling, or aspirin or both.
Aggregation of thrombocytes (platelets). Platelet-rich human blood plasma (left vial) is a turbid liquid. Upon addition of ADP, platelets are activated and start to aggregate, forming white flakes (right vial) Hemostasis occurs when blood is present outside of the body or blood vessels.