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BLOOD. RBCs. Figure 12-68. The availability of dietary iron can be a limiting factor in erythropoiesis, so storage and recycling mechanisms are highly developed in humans, as protection from anemia. Figure 12-69. Erythropoiesis is hormonally regulated:
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Figure 12-68 The availability of dietary iron can be a limiting factor in erythropoiesis, so storage and recycling mechanisms are highly developed in humans, as protection from anemia.
Figure 12-69 Erythropoiesis is hormonally regulated: decreased oxygen delivery to the kidney causes the secretion of erythropoietin, which activates receptors in bone marrow, leading to an increase in the rate of erythropoiesis.
Figure 12-70 The major forms of “cells” in the blood. Among these, only the leukocytes are true cells with nuclei.
Figure 12-71 Stem cells in the bone marrow constitute an important precursor of many of the formed components in the blood.
Figure 12-72 Signaling mediates responses to damage in a blood vessel: collagen is a “magnet for platelets,” which then become one of the sources of signals that alter blood flow and initiate the steps of clot formation at the affected site.
Figure 12-73 Signaling mediates responses to damage in a blood vessel: adjacent endothelial cells are a source of signals that influence platelet aggregation and alter blood flow and clot formation at the affected site.
Figure 12-76 Knowledge that thrombin plays a central role in clotting has generated detailed studies of the possible pathways resulting in its formation: the extrinsic pathway is the more important of the two under most circumstances.
Figure 12-77 The liver plays a critical role in producing and modifying blood-borne proteins, including those used in the clotting pathway. Moreover, bile salts from the liver facilitate the absorption of lipids in the diet, including vitamin K, which is required for the synthesis of prothrombin.
Figure 12-78 In an uninjured vessel, thrombin bound to thrombomodulin activates protein C, which blocks the clotting response.
Figure 12-79 Following tissue repair, fibrin clots are dissolved in a process mediated by plasmin; synthetic plasminogen activators can be used immediately after a stroke or heart attack to help dissolve clots and restore blood flow.
