Which of the following factors can cause blood pressure to drop to normal levels?
A. Kidneys’ excretion of sodium only.
B. Kidneys’ retention of sodium and water.
C. Kidneys’ excretion of sodium and water.
D. Kidneys’ retention of sodium and excretion of water
Correct Answer: C. Kidneys’ excretion of sodium and water
The kidneys respond to a rise in blood pressure by excreting sodium and excess water. This response ultimately affects systolic pressure by regulating blood volume. The renin-angiotensin-aldosterone system is an essential regulator of arterial blood pressure. The system relies on several hormones that act to increase blood volume and peripheral resistance.
Option A: In response to acute changes in blood pressure, the body responds through the baroreceptors located within blood vessels. Baroreceptors are a form of mechanoreceptor that become activated by the stretching of the vessel. This sensory information is conveyed to the central nervous system and used to influence peripheral vascular resistance and cardiac output.
Option B: The antidiuretic hormone produced in the hypothalamus makes its way down the pituitary stalk to the posterior pituitary where it is kept in reserve for release in response to the above-listed triggers. ADH mainly functions to increase free water reabsorption in the collecting duct of the nephrons within the kidney, causing an increase in plasma volume and arterial pressure.
Option D: Angiotensin II has many functions to increase arterial pressure, including increased sodium reabsorption within the kidney tubules. The increased sodium reabsorption from the kidney tubules results in passive reabsorption of water through osmosis; this causes an increase in blood volume and arterial pressure.
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