Blood Figs and Innate Immune(7 pages)
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Blood Figs and Innate Immune
- Lecture number:
- Lecture Note
- University of Southern California
- Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 30 Current Lecture Hematopoiesis Blood cells come from the bone marrow. Red bone marrow, in fetal life, create red blood cells. After birth, however, most red bone marrow converts to yellow bone marrow, except for a few of the long bones(pelvis, etc.), which retain the ability to make red blood cells. The rest of the bone marrow is yellow bone marrow, which is used in fat storage. You have various levels of commitment of stem cells(top left): pluripotent hematopoietic stem cells, which proliferate and become uncommitted stem cells, which become committed to give rise to certain mature blood types but remain stem cells, and continue to proliferate. One of the daughter cells then becomes fully committed, becoming a progenitor of a full cell – these are NOT stem cells, they mature into mature cell types. Neutrophils are shown, as are RBC’s and a megakaryocyte, which stays in the bone marrow and buds off platelets. Can see a monocyte, which will give rise to a macrophage. The hematopoiesis of these different cell types is controlled by hematopoietic cytokines (hormones of the immune system). One example is erythropoietin, which stimulates the production of erythrocytes. Another is thrombopoietin, which stimulates the megakaryocytes and therefore the platelets to develop, and then there are a variety of cytokines called colony stimulating factors, or interleukines, and they stimulate all the blood cell types in different ratios. They are produced in prestigious numbers – the most abundant blood cells are the erythrocytes (have a life span of 90-120 days, after which they are destroyed, so there is a substantial production of RBC’s all the time). The cell type being produced at the highest rate are the neutrophils. They have a life span of a few hours, so they must be produced rapidly. Hemostasis The viscosity of the blood can’t be too high, or it can’t flow freely. And it definitely should not clot – if it clots incorrectly then resistance would go up greatly and problems would ensue. But it also has to be able to clot to stop leaks. Hemostasis, the cessation of bleeding, is a five step process: 1.) Vasoconstriction 2.) Platelet plug formation 3.) Coagulation 4.) Tissue repair 5.) Thrombolysis The process begins with damage to the wall of the blood vessel. The damage to any smooth muscle cells that happen to be in the vessel is going to cause vasoconstriction, which will minimize blood loss in that area. (left hand path) Blood is normally only in contact with the endothelium, except when the vessel is damaged. Two abundant proteins in the layers of the blood vessel wall outside the lumen are collagen and tissue factor. The exposure of collagen and tissue factor to platelets is going to trigger clotting. Tissue factor is also known as coagulation or clotting factor three, or thromboplastin. When platelets contact collagen, they bind to them by means of integrins, which are membrane proteins that bind to certain 3 amino acid sequences in extracellular ...
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