Hematopoiesis Blood cell formation Occurs in red bone marrow

Hematopoiesis Hemocytoblast differentiation: Lymphoid stem Myeloid stem c

Figure 10.4 Hematopoiesis

Formation of Erythrocytes Unable to divide, grow, or synthesize proteins Wear out in 100 to 120 days When worn out, RBCs are eliminated by phagocytes in the spleen or liver Lost cells are replaced by division of hemocytoblasts in the red bone marrow

Control of Erythrocyte Production Erythropoietin Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood

Control of Erythrocyte Production Figure 10.5 Reduced O 2 levels in blood Stimulus: Decreased RBC count, decreased availability of O 2 to blood, or increased tissue demands for O 2 Increased O 2 - carrying ability of blood Erythropoietin stimulates Kidney releases erythropoietin Enhanced erythropoiesis Red bone marrow More RBCs Normal blood oxygen levels Imbalance

Formation of White Blood Cells and Platelets Controlled by hormones Colony stimulating factors (CSFs) and interleukins prompt bone marrow to generate leukocytes Thrombopoietin

Hemostasis Stoppage of bleeding resulting from a break in a blood vessel Hemostasis involves three phases Vascular spasms Platelet plug formation Coagulation (blood clotting)

Hemostasis Vascular spasms Vasoconstriction – spasms

Hemostasis Platelet plug formation Collagen fibers are exposed Platelets become “ sticky ” and cling to fibers

Hemostasis Figure 10.6, step 3 Injury to lining of vessel exposes collagen fibers; platelets adhere Platelet plug forms Collagen fibers Platelets Step 1: Vascular Spasms Step 2: Platelet Plug Formation

Hemostasis Figure 10.6, step 4 Injury to lining of vessel exposes collagen fibers; platelets adhere Platelet plug forms Platelets release chemicals that attract more platelets to the site and make nearby platelets sticky Collagen fibers Platelets PF 3 from platelets Calcium and other clotting factors in blood plasma Tissue factor in damaged tissue Step 1: Vascular Spasms Step 2: Platelet Plug Formation +

Hemostasis Figure 10.6, step 7 Platelets release chemicals that attract more platelets to the site and make nearby platelets sticky PF 3 from platelets Calcium and other clotting factors in blood plasma Formation of prothrombin activator Prothrombin Fibrinogen (soluble) Fibrin (insoluble) Thrombin Tissue factor in damaged tissue Phases of coagulation (clotting cascade) +

Hemostasis Coagulation Injured tissues release tissue factor (TF) PF 3 (a phospholipid) interacts with TF Prothrombin activator converts prothrombin to thrombin (an enzyme)

Hemostasis Coagulation (continued)

Hemostasis Figure 10.7

Hemostasis Blood usually clots within 3 to 6 minutes The clot remains as endothelium regenerates The clot is broken down after tissue repair