The Cardiovascular System: Blood Vessels 455 Figure 19.1 A. B. C.
The Correct Answer and Explanation is:
Correct Answers for Figure 19.1:
- A. Artery
- B. Vein
- C. Capillary
Explanation
Figure 19.1 illustrates the structural differences among the three main types of blood vessels in the cardiovascular system: arteries, veins, and capillaries. Understanding these differences is crucial to comprehending how blood is transported throughout the body.
A. Artery
The first image (A) shows a vessel with a thick muscular and elastic wall. Arteries must withstand and regulate the high pressure generated by the heart as it pumps blood. Their walls are composed of three layers: the innermost tunica intima, the middle tunica media (which is especially thick with smooth muscle and elastic fibers), and the outer tunica externa. This thick wall maintains blood pressure and allows for the elastic recoil necessary during the cardiac cycle.
B. Vein
The second image (B) displays a vessel with a thinner tunica media and a wider lumen compared to arteries. Veins return blood to the heart under low pressure, so they do not need thick walls. They often contain valves (seen in the drawing) to prevent the backflow of blood, especially in the limbs. The thinner muscle layer allows veins to act as blood reservoirs, holding much of the body’s blood volume at any given time.
C. Capillary
The third image (C) shows a single-layered vessel — the capillary. Capillaries consist of only the tunica intima, which is made up of a single layer of endothelial cells. This thin structure allows for the efficient exchange of gases (like oxygen and carbon dioxide), nutrients, and wastes between the blood and surrounding tissues. Capillaries are the smallest blood vessels and form vast networks called capillary beds that penetrate tissues to ensure every cell is near a blood supply.
In summary, arteries are built for high pressure, veins for low pressure and volume return, and capillaries for exchange. Their structure directly reflects their function in the circulatory system.
