National Physical Therapy Examination (NPTE) Practice Exam

What chemical is stimulated to act as a vasoconstrictor in response to decreased arterial pressure?

1. Angiotensin

2. Epinephrine

3. Norepinephrine

4. Histamine

The correct answer is: Angiotensin

Angiotensin is a key player in the body's response to decreased arterial pressure. When blood pressure drops, the kidneys detect this decrease and release renin, an enzyme that catalyzes the conversion of angiotensinogen, a protein produced by the liver, into angiotensin I. Angiotensin I is subsequently converted into angiotensin II by an enzyme called ACE (angiotensin-converting enzyme) primarily in the lungs. Angiotensin II acts as a potent vasoconstrictor, narrowing blood vessels and thereby increasing blood pressure. Additionally, it stimulates the adrenal glands to release aldosterone, which promotes sodium and water retention, further assisting in raising blood pressure. This biological pathway illustrates how angiotensin directly contributes to the body's mechanism for restoring blood pressure to normal levels through vasoconstriction and fluid retention. In contrast, while epinephrine and norepinephrine also play roles in vasoconstriction and responding to changes in blood pressure, they are primarily released in response to stress or the "fight-or-flight" response, rather than directly in response to decreased arterial pressure. Histamine, on the other hand, is generally involved in inflammatory responses and leads to vasodilation rather than vasoconstriction.