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.

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.