Essentials of Anatomy and Physiology

Regulation of Blood Pressure—intrinsic
mechanisms and nervous mechanisms
Intrinsic Mechanisms

1. The heart—responds to increased venous return by
   pumping more forcefully (Starling’s law), which
   increases cardiac output and BP.


2. The kidneys—decreased blood flow decreases
   filtration, which decreases urinary output to pre-
   serve blood volume. Decreased BP stimulates the
   kidneys to secrete renin, which initiates the renin-
   angiotensin mechanism (Table 13–3 and Fig.
   13–12) that results in the formation of angiotensin
   II, which causes vasoconstriction and stimulates
   secretion of aldosterone.

Nervous Mechanisms (see Fig. 13–13)

1. Heart rate and force—see also Chapter 12.


2. Peripheral resistance—the medulla contains the
   vasomotor center, which consists of a vasoconstric-
   tor area and a vasodilator area. The vasodilator area
   brings about vasodilation by suppressing the vaso-
   constrictor area. The vasoconstrictor area main-
   tains normal vasoconstriction by generating several
   impulses per second along sympathetic vaso-
   constrictor fibers to all arteries and veins. More
   impulses per second increase vasoconstriction and
   raise BP; fewer impulses per second bring about
   vasodilation and a drop in BP.

The Vascular System 317

REVIEW QUESTIONS

1. Describe the structure of the three layers of the
   walls of arteries, and state the function of each
   layer. Describe the structural differences in these
   layers in veins, and explain the reason for each dif-
   ference. (p. 292)


2. Describe the structure and purpose of anasto-
   moses, and give a specific example. (pp. 292–293)


3. Describe the structure of capillaries. State the
   process by which each of the following is
   exchanged between capillaries and tissue fluid:
   nutrients, oxygen, waste products, and carbon
   dioxide. (pp. 293–295)


4. State the part of the body supplied by each of the
   following arteries: (pp. 297, 300)
   a. Bronchial
   b. Femoral
   c. Hepatic
   d. Brachial
   e. Inferior mesenteric
   f. Internal carotid
   g. Subclavian
   h. Intercostal


5. Describe the pathway of blood flow in hepatic por-
   tal circulation. Use a specific example to explain the
   purpose of portal circulation. (pp. 301, 304)


6. Begin at the right ventricle and describe the path-
   way of pulmonary circulation. Explain the purpose
   of this pathway. (p. 296)
   7. Name the fetal structure with each of the follow-
   ing functions: (pp. 303–305)
   a. Permits blood to flow from the right atrium to
   the left atrium
   b. Carries blood from the placenta to the fetus
   c. Permits blood to flow from the pulmonary
   artery to the aorta
   d. Carry blood from the fetus to the placenta
   e. Carries blood from the umbilical vein to the
   inferior vena cava
   8. Describe the three mechanisms that promote
   venous return when the body is vertical.
   (pp. 307–308)
   9. Explain how the normal elasticity of the large
   arteries affects both systolic and diastolic blood
   pressure. (p. 309)


7. Explain how Starling’s law of the heart is involved
   in the maintenance of blood pressure. (p. 307)


8. Name two hormones involved in the maintenance
   of blood pressure, and state the function of each.
   (p. 309)


9. Describe two different ways the kidneys respond
   to decreased blood flow and blood pressure.
   (p. 311)


10. State two compensations that will maintain blood
    pressure after a small loss of blood. (p. 309)


11. State the location of the vasomotor center and
    name its two parts. Name the division of the