20.6b Renin-Angiotensin System

What is the renin-angiotensin system?

A hormonal system that regulates blood pressure and blood volume.

What does the liver produce in this system?

Angiotensinogen.

What is angiotensinogen?

An inactive protein released into the blood.

When do the kidneys release renin?

In response to low blood pressure or sympathetic activity.

What enzyme do the kidneys release?

Renin.

What does renin do?

It converts angiotensinogen to angiotensin I.

What enzyme converts angiotensin I to angiotensin II?

Angiotensin-converting enzyme (ACE).

Where is ACE primarily located?

In capillaries of the lungs.

What is angiotensin II?

A hormone that raises blood pressure.

How does angiotensin II affect blood vessels?

It acts as a vasoconstrictor.

What is the effect of vasoconstriction on blood pressure?

It increases resistance and raises blood pressure.

How does angiotensin II affect thirst?

It stimulates the thirst center.

How does increased thirst affect blood pressure?

It increases fluid intake and blood volume.

How does angiotensin II affect the kidneys?

It decreases urine formation.

Why does decreasing urine formation increase blood pressure?

More fluid is retained in the blood.

Which hormones are stimulated by angiotensin II?

ADH and aldosterone.

What do ADH and aldosterone do?

They reduce urine output and increase blood volume.

What is the overall effect of angiotensin II, ADH, and aldosterone?

They increase blood pressure by increasing volume and resistance.