Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 273 of 367 Age-related changes in blood vessels may be associated with arteriosclerosis: the inelastic walls of arteries become less tolerant of sudden pressure increases, which can lead to an aneurysm, whose rupture may (depending on the vessel) cause a stroke, myocardial infarction, or massive blood loss;calcium salts can be deposited on weakened vascular walls, increasing the risk of a stroke or myocardial infarction; and thrombi can form at atherosclerotic plaques. 20.17 Chapter Twenty Review Arteries, arterioles, capillaries, venules, and veins differ in size, structure, and functional properties: • Blood travels through a network of arteries, veins, and capillaries. All chemical and gaseous exchange between blood and interstitial fluid occurs across capillary walls. • Arteries and veins form an internal distribution system through which the heart propels blood. Arteries branch regularly, decreasing in size until they become arterioles. From the arterioles, blood goes into capillary networks. Blood flowing from the capillaries goes into small venules before entering larger veins. • The walls of arteries and veins have three layers: the innermost tunica intima, the tunica media, and the outermost tunica externa. • In general, the walls of arteries are thicker than those of veins. Arteries constrict when blood pressure does not distend them; veins constrict very little. The endothelial lining cannot contract, so when constriction occurs, the lining of an artery is thrown into folds. 20.15 Fetal Circulation in the Heart and Great Vessels One of the most interesting aspects of circulatory development reflects the differences between the life of an embryo or fetus and that of an infant. Throughout embryonic and fetal lives, the lungs are collapsed; after delivery, the newborn infant must be able to receive oxygen from inspired air rather than across the placenta. Although the interatrial and interventricular septa develop early in fetal life, the interatrial partition remains functionally incomplete until birth. 20.16 Aging Aging affects the blood, heart, and blood vessels. The capabilities of the cardiovascular system gradually decline. As you age, your cardiovascular system undergoes the following major changes: • Age-related changes in blood may include a decreased hematocrit; constriction or blockage of peripheral veins by a thrombus (stationary blood clot), which can become detached, pass through the heart, and become wedged in a small artery (commonly in the lungs), causing pulmonary embolism; and pooling of blood in the leg veins because valves are not working effectively. • Age-related changes in the heart include a reduction in maximum cardiac output; changes in the activities of nodal and conducting cells; a reduction in the elasticity of the cardiac (fibrous) skeleton; progressive atherosclerosis that can restrict coronary circulation; and replacement of damaged cardiac muscle cells by scar tissue. •