Platelets

Formation of Platelets

Formation of platelets occurs in the bone marrow. The cytokine that is key here is TPO, thrombopoietin, which regulates platelet levels. It is secreted by the liver. All hematopoietic cell lineages have a self-regenerating stem cell that subsequently replicates and divides forming more committed cell lineages. One of which is colony forming unit (CFU) GEMMK, then CFU-EMMK, then CFU-MK, colony forming unit  megakaryoctye Finally producing a megakaryoblast which has dupliacte nuclear material, 2n. Then occurs megakaryocte differentiation and finally megakaryoctes. Overall, there is proliferation and nuclear endoreplication, which is division of the nucleus and an increase in cell size. Megakaryoctes are polyploidy, which is a way to create a very large cell with a big mass. These cells release anucleated cells, termed platelets into the circulation that are involved in primary hemostasis. Which a nucleus, these cells are unable to make proteins.

Structure of Platelets

Platelets do not have a nucleus, and are the smallest cells in the blood. They do have many organelles adn storage granules. There purpose is to aggregate and block blood flow. Platelets are formed by microtubules, which coil to maintain the shape of the platelet. Theree is a dense tubular system, glycogen which are energy stores for the cell, lysosomes, mitochondria, dense bodies which contain ADP, calcium, serotonin, alpha granules which contain fibrinogen, von Willebrand factor, platelet factor 4, and a plasma membrance which was taken while budding from the megakaryocyte. When a platelet is stimulated to aggregate, is releases the contents of its storage granules, which are mentiioned above, both the dense bodies and the alpha granules.

Platelet Function

Hemostasis is the physiological response, in which stoppagge of blood flow from a cut or severed vessel by a platelet plug. Thrombosis, arterial thrombosis, white thrombi which are platelet-rich, and also venous throbosis, which are red thrombi, because they are red blood cell rich. Moreover, thromboembolism is when bits of thrombi are broken off and move downstream. Emboli are bits of thrombi that can occlude smaller vessels.

There are 3 steps in the formation of a hemostatic plug by arterial thrombus. The first step is adhesion to collagen which activates platelets and changes their shape. Secretion of granule conteents. ADP is a platelet aggregating agent, and aggregation through stimulated by these granule contents, ADP and TXA2, thromboxane A2.
Platelets do not adhere to normal vessel walls, but only recognize subendothelial structures. Fibrin can then bind to platelets to stabilize them into a platelet plug. Fibrin can then be degraded by plasmin into degradation products and dissolve a thrombus or clot.