Biomedical Engineering Reference
In-Depth Information
FIGURE 8-2
The
cardiovascular
system.
spread to contractile cells via gap junctions. A dense network of blood vessels surrounds
the heart and supplies the respiring cardiac tissues with essential oxygen and nutrients and
also removes metabolic waste products. The heart's role as a pumping device is considered
in more detail later in this chapter.
There are three main types of blood vessels:
• Arteries—the afferent blood vessels that carry blood away from the heart
• Veins—the efferent blood vessels that return blood to the heart
• Capillaries—narrow, thin-walled blood vessels that form networks within the
tissues
As shown in Figure 8-2, arteries branch and diverge as the distance from the heart
increases. Smaller and smaller divisions are formed that eventually terminate in capillaries.
By contrast, capillaries merge to form veins and further converge into successively larger
blood vessels as the distance back toward the heart decreases. Capillary networks are the
site of gas, nutrient, and waste exchange between the blood and the respiring tissues.
8.2
THE HEART AS A PUMP
The heart can be considered a pair of pumps folded together to form a single unit, as shown
in Figure 8-3:
•
The right half of the heart pumps blood only to the lungs. Deoxygenated blood
enters the right atrium through the superior and inferior vena cavae and then out
from the right ventricle into the pulmonary arteries at low pressure (25 mm Hg).
