Which of the following increases due to the action of angiotensin II?

Angiotensin II plays a crucial role in the regulation of blood pressure and fluid balance within the body. One of its primary functions is to increase blood volume. It does this by promoting the reabsorption of sodium in the kidneys. When sodium is reabsorbed, water follows passively due to osmotic forces, leading to an increase in blood volume. This increase in blood volume, in turn, raises blood pressure, which is essential for maintaining adequate blood flow to organs.

Additionally, angiotensin II stimulates the release of aldosterone from the adrenal glands, further enhancing sodium reabsorption and potassium excretion in the kidneys. The action of angiotensin II also leads to increased thirst, adding to fluid intake, which supports the increase in blood volume.

While changes in heart rate, sodium excretion, and venous return may occur in response to the overall regulatory effects of the renin-angiotensin system, the most direct and specific outcome of angiotensin II action is the increase in blood volume. This is a critical adaptation for ensuring sufficient perfusion pressure in times of low blood pressure or blood volume, protecting the body's tissues and organs from ischemia.