Vascular System

Vascular System

After studying this chapter, readers should be able to

1. Distinguish the structures and functions of various blood vessels.

2. Explain the difference between pulmonary and systemic vessels.

3. Define blood flow, blood pressure, and resistance.

4. Describe the effects of the sympathetic and parasympathetic nervous systems on the blood vessels.

5. Describe the factors that influence blood pressure and explain how blood pressure is regulated.

6. List the major arteries that supply the head and abdomen.

7. Identify the main arteries and veins of the lower limbs.

8. List the major veins that carry blood away from the lower limbs.

9. Describe the hepatic portal system.

10. Define pulse pressure and list locations on the body surface where the pulse can be detected

Overview

Blood moves on a continual basis through the heart, arteries and their smaller branches, capillaries, thesmaller vein branches, and then the veins themselves, returning back to the heart. The blood vessels con-strict, relax, and pulsate as they conduct blood and other substances to the body tissues. All body tissues require circulation to survive. FIGURE 19-1 shows the relationship between various blood vessels in the body.

 The five general classes of blood vessels in the cardiovascular system are the arteries, arterioles, capillar-ies, venules, and veins. In total, the blood vessels of an average human adult, if stretched out, are about 60,000 miles in length. Arteries are very strong elastic vessels that are able to carry blood away from the heart under high pressure. They subdivide into thinner tubes that give rise to branched, finer arterioles. Terms used to describe the subdivision of arteries include “fork,” “branch,” and “diverge.” In the systemic circuit, the arteries carry only oxygenated blood, whereas the veins carry only deoxygenated blood. In the pulmonary­circuit, the reverse is true. In a fetus, there are unique umbilical vessels that have differing roles of their arteries and veins.

For children and adults, the arterioles lead to the capillaries, which are the only blood vessels that closely contact tissue cells and serve the needs of the cells. The extremely thin capillary walls allow most exchanges that occur between blood and tissue cells. When oxygenated blood leaves the alveolar capillaries, it enters the venules, which eventually unite to form larger blood vessels, transporting blood to the pulmonary veins. The veins become larger as they proceed to the extremely large veins emptying into the heart. Terms used to describe the uniting of veins include “merge,” “converge,” and “join.” The pulmonary circuit is completed by the four pulmonary veins, two from each lung, that empty into the left atrium to complete the pulmonary circuit.