What is the role of angiotensin II in the cardiovascular system?

The role of angiotensin II in the cardiovascular system primarily involves its function as a potent vasoconstrictor. When angiotensin II is released, it constricts blood vessels, which significantly increases the resistance that the heart must overcome to pump blood. This direct vasoconstriction elevates blood pressure, making it a critical component of blood pressure regulation, especially during states of low blood volume or low blood pressure—such as dehydration or hemorrhage.

Angiotensin II also stimulates the release of aldosterone, a hormone that promotes sodium and water retention by the kidneys. This leads to an increase in blood volume, further contributing to increased blood pressure.

While other choices mention vasodilation, heart rate, and immune response, they do not accurately represent the main action of angiotensin II, which is the promotion of vasoconstriction. Its primary purpose in the cardiovascular system is to restore and maintain blood pressure and volume, especially during hypotensive events.