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49 Circulatory Systems: Pumps, Vessels, and Blood • In open circulatory systems, the blood or circulating fluid is not kept separate from the tissue fluid. • The most simple systems squeeze tissue fluid through and around intercellular spaces. • Arthropods, mollusks, and other invertebrates utilize this type of circulatory system. 49 Circulatory Systems: Pumps, Vessels, and Blood • A closed circulatory system keeps the blood and tissue fluid separate. • One or more muscular hearts and a branching network of vessels (the vascular system) move the blood. • There are different types. In-Text Art, p. 943(1) In-Text Art, p. 943(3) In-Text Art, p. 944(1) In-Text Art, p. 944(2) 49 Vertebrate Circulatory Systems • The four-chambered hearts of birds and mammals completely separate the pulmonary and systemic circuits. • The advantages of separate circuits are: Oxygenated and deoxygenated blood cannot mix. Gas exchange is maximized because the lungs receive only blood with low O2 and high CO2 content. In-Text Art, p. 945 Figure 49.3 The Human Heart and Circulation (Part 2) 49 The Human Heart: Two Pumps in One • The right atrium receives blood from the superior and inferior vena cavas. • From the right atrium, blood goes to the right ventricle. • The right ventricle sends blood through the pulmonary artery to the lung. • Pulmonary veins return oxygenated blood to the left atrium. • From the left atrium, blood goes to the left ventricle. • The left ventricle sends blood through the aorta to the body and the capillary beds. • Blood returns to the right atrium via veins. Figure 49.7 The Heartbeat Figure 49.10 Anatomy of Blood Vessels (Part 1) Figure 49.13 One-Way Flow 49 Blood: A Fluid Tissue • Blood is connective tissue: it consists of living cells within an extracellular matrix. • The fluid matrix is called plasma. • The cellular components of blood are the red blood cells (erythrocytes), the white blood cells (leukocytes), and the platelets (cell fragments). Figure 49.15 The Composition of Blood 49 Blood: A Fluid Tissue • Most of the cells in blood are erythrocytes. • At maturity they are biconcave, flexible discs packed with hemoglobin. • The hemoglobin carries O2, and the flexible shape of the cell lets them squeeze through narrow capillaries. 49 Blood: A Fluid Tissue • Bone marrow makes about 2 million red blood cells per second. • Each red blood cell lives about 120 days and then breaks down. • The spleen serves as a reservoir for old blood cells that have been squeezed and ruptured. The cell remnants are then broken down by macrophages. 49 Blood: A Fluid Tissue • Cell damage leads to conversion of an inactive enzyme in the blood, prothrombin, to its active form, thrombin. • Thrombin causes a plasma protein, fibrinogen, to polymerize, forming fibrin threads. • These threads form a meshwork to seal the damaged vessel and provide a base for scar tissue. Figure 49.16 Blood Clotting (Part 2) 49 Blood: A Fluid Tissue • Plasma contains gases, ions, nutrients, proteins, hormones, and other chemicals. • Nutrient molecules in plasma include glucose, amino acids, lipids, lactic acid, and cholesterol. • Circulating proteins include albumin, antibodies, hormones, and carrier molecules.