The most important factor in regulating the caliber of blood vessels, which determines resistance to flow, is:
A. Hormonal secretion
B. Independent arterial wall activity.
C. The influence of circulating chemicals
D. The sympathetic nervous system
Correct Answer: D. The sympathetic nervous system
The autonomic nervous system exerts influence over the organ systems of the body to upregulate and downregulate various functions. The two aspects of the ANS operate as opposing functions that act to achieve homeostasis. The sympathetic nervous system, also known as the “fight or flight” system, increases energy expenditure and inhibits digestion.
Option A: Hormones of the endocrine system are a vast topic with numerous hormones involved, affecting virtually every organ in the human body. Human physiological processes such as homeostasis, metabolic demand, development, and reproduction are all possible because of hormones and the processes mediated by their actions.
Option B: A major role of large arteries is to dampen the pressure oscillations resulting from intermittent LV ejection, which transforms highly pulsatile flow and pressure into a pattern of more continuous flow in peripheral tissues and organs. During systole, roughly 40% to 50% of stroke volume is forwarded directly to peripheral tissues, whereas the remainder is stored in the distended aorta and central arteries. Approximately 10% of the energy produced by the heart is diverted for the distension of arteries and “stored” in the walls.
Option C: The microcirculation deserves special attention since it is across the walls of these vessels that the exchange of oxygen, among other substances, takes place. Furthermore, the arterioles, also known as the “resistance” vessels, are the primary site for control of blood flow. Thus, the blood vessels of the microcirculation play important roles in both the convective (arterioles) and diffusive (capillaries) transport of oxygen.
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