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Platelet1 - Hemostasis Hemostasis is the homeostatic...

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Platelets In contrast to the number of erythrocytes per uL , platelets number about 250,000/uL. Although this number is smaller, they are still essential for survival, as platelets are responsible for hemostasis . Specifically, platelets serve a number of functions: they aid in vascular constriction , platelet plug formation, and coagulation . They are also important in tissue repair, WBC recruitment and dissolution of clots. Thrombopoiesis During thrombopoiesis , hemocytoblasts that express receptors for thrombopoietin differentiate into megakaryoblasts. Thrombopoietin stimulates these cells to repeatedly replicate their DNA without dividing, resulting in a megakaryocyte that remains in the red bone marrow. Infoldings of the megakaryocyte cytoplasm split off cell fragments that enter the bloodstream as platelets. Platelets are essentially small envelopes of cell membrane surrounding cytoplasm and granules . Platelets circulate for about 10 days and some are stored in the spleen to be released as needed.
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Unformatted text preview: Hemostasis Hemostasis is the homeostatic mechanism that prevents the loss of blood due to trauma or other damage to blood vessels. It is effective in small vessels, although larger vessels may require medical intervention to prevent serious damage or death. The three stages of homeostasis are vascular spasm , platelet plug formation and coagulation . (See Figure 5). Figure 5 Vascular Spasm Vascular spasms promote the prompt constriction of a broken blood vessel. Several stimuli cause this constriction. Pain receptors not only signal to the brain that damage has occurred, but also to the smooth muscle layer of the damaged vessel to cause constriction. This type of stimulation may only last a few minutes; more long-lasting constriction is chemically stimulated. Platelets respond to endothelin released by damaged endothelial cells and release serotonin , which is a potent vasoconstrictor. The vascular spasm stage of hemostasis allows time for the other two mechanisms to work....
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