49 circulatory systems: pumps, vessels, and blood in open circulatory systems, the blood or...
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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.
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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.
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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.