Chapter 16

Blood is an interesting tissue, with blood cells and cell fragments that forms one of the two extracellular compartments. Exchange between the plasma and interstitial fluid takes place only in the capillaries. Bulk flow of blood through the body depends on the pressure gradient created by the heart. At the same time, high pressure in the blood vessels poses a danger should the wall of a vessel rupture. Collectively, the cellular and protein components of blood carry out hemostasis and coagulation to protect against excessive blood loss. Blood cells are also essential for oxygen transport and defense, as you will learn in later chapters. 16.1 Plasma and the Cellular Elements of Blood 1. Blood is the circulating portion of the extracellular compart-ment. (p. 511) 2. Plasma, the liquid matrix of blood, is composed mostly of water, with dissolved proteins, organic molecules, ions, and dissolved gases. (p. 511; Fig. 16.1) 3. The plasma proteins include albumins, globulins, and the clotting protein fibrinogen. They function in blood clotting, defense, and as hormones, enzymes, or carriers for different sub-stances. (p. 511) 4. The cellular elements of blood are red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. Platelets are fragments of cells called megakaryocytes. (p. 513; Fig. 16.1) 5. Blood contains five types of white blood cells: (1) lymphocytes, (2) monocytes, (3) neutrophils, (4) eosinophils, and (5) basophils. (p. 513; Fig. 16.1) 16.2 Blood Cell Production 6. All blood cells develop from a pluripotent hematopoietic stem cell. (p. 513; Fig. 16.2) 7. Hematopoiesis begins early in embryonic development and con-Linues throughout a person's life. Most hematopoiesis takes place in the bone marrow. (p. 513; Fig. 16.4) 8. Colony-stimulating factors and other cytokines control white blood cell production. Thrombopoietin regulates the growth and maturation of megakaryocytes. Red blood cell production is regulated primarily by erythropoietin. (p. 515) 16.3 Red Blood Cells 9. Mature mammalian red blood cells are biconcave disks lacking a nucleus. They contain hemoglobin, a red oxygen-carrying pigment. (p. 517; Fig. 16.5) 10. Hemoglobin synthesis requires iron in the diet. Iron is transported in the blood on transferrin and stored mostly in the liver on the protein ferritin. (p. 517; Fig. 16.6) 11. When hemoglobin is broken down, some heme groups are converted into bilirubin, which is incorporated into bile and excreted. Elevated bilirubin concentrations in the blood cause jaundice. (p. 519; Fig. 16.6) 16.4 Platelets 12. Platelets are cell fragments filled with granules containing clotting proteins and cytokines. Platelets are activated by damage to vascular endothelium. (p. 522; Fig. 16.7) 16.5 Hemostasis and Coagulation 13. Hemostasis begins with vasoconstriction and the formation of a platelet plug. (p. 523; Fig. 16.8) 14. Exposed collagen triggers platelet adhesion and platelet aggregation. The platelet plug is converted into a clot when reinforced by fibrin. (p. 523; Fig. 16.8) 15. In the last step of the coagulation cascade, fibrin is made from fibrinogen through the action of thrombin. (p. 525; Fig. 16.10) 16. As the damaged vessel is repaired, plasmin trapped in the platelet plug dissolves fibrin (fibrinolysis) and breaks down the clot. (p. 525; Fig. 16.11) 17. Platelet plugs are restricted to the site of injury by prostacyclin in the membrane of intact vascular endothelium. Anticoagulants limit the extent of blood clotting within a vessel.