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Chapter 21 Questions: 21, 38, 48, 50, 58
21. What areas of the3 body are supplied by the paired arteries that branch from the abdominal aorta? The unpaired arteries? Name the three major unpaired branches.
The paired visceral branches of the abdominal aorta supply the kidneys, the adrenal glands, and the gonads. The parietal arteries of the abdominal aorta supply the diaphragm and the abdominal wall. Three major unpaired branches exist: the celiac trunk, the superior mesenteric artery, and the inferior mesenteric artery. Each has several major branches supplying the abdominal organs.
38. Define vascular compliance. Do veins or arteries have a greater compliance?
Vascular compliance is the tendency for blood vessel volume to increase as the blood pressure increases. The more easily the vessel wall stretches, the greater its compliance. Veins have a greater compliance. Veins act as storage areas, or reservoirs, for blood because their large compliance allows them to hold much more blood than other areas of the vascular system.
48. How do blood volume and venous tone affect cardiac output?
If blood volume is increased because of a rapid transfusion, the amount of blood flow to the heart through the veins increases. A rapid loss of a large volume of blood decreases venous return to the heart, which decreases the preload and cardiac output. Increased sympathetic stimulation increases venous tone by causing constriction which forces the large venous volume to flow toward the heart. This increase in venous volume results in an increase in cardiac volume. A decrease in sympathetic stimulation results in less venous tone and less return to the heart causing decreased cardiac output.
50. Explain how vasodilator substances and nutrients are involved with local control of blood flow. What is vasomotion? What is auto regulation of local blood flow?
As the rate of metabolism increases in a tissue, blood flow through its capillary increases as well. Vasodilator substances are produced as the rate of metabolism increases. The vasodilator substances then diffuse from the tissues supplied by the capillary and cause vasodilation. Several chemicals, including carbon dioxide, lactic acid, adenosine, adenosine monophosphate, adenosine diphosphate, endothelium-derived relaxation factor, potassium ions, and hydrogen ions, cause vasodilation, and they increase the concentration of the extracellular fluid as the rate of metabolism in tissues increases. Smooth muscle cells relax as a response to a lack of oxygen and other nutrients, resulting in vasodilation. Vasomotion is the periodic contraction and relaxation of the precapillary sphincters resulting in cyclic fluctuation of blood flow through the capillaries. The maintenance of blood flow by tissues is called auto regulation, which causes blood flow through tissues to remain relatively constant.


58. Where are the chemoreceptor for carbon dioxide, pH, and oxygen located? Describe what happens when oxygen levels in the blood decrease.
Chemoreceptors are located in the carotid and aortic bodies. When oxygen availability decreases in the chemoreceptor cells, the frequency of action potentials increases and stimulates the vasomotor center, resulting in increased vasomotor tone. This increase tone cause an increase in venous blood pumped to the heart, resulting in an increased cardiac output.