AAMC FL Practice Exam

Atrial natriuretic peptide (ANP) is released primarily in response to excess blood volume. When there is an increase in blood volume, which can occur due to various factors such as high sodium intake or fluid retention, the heart's atrial cells detect this stretch or distension. This stretching stimulates the release of ANP, which plays a crucial role in regulating blood pressure and fluid balance in the body.

Once released, ANP acts to promote vasodilation, which helps lower blood pressure, and enhances renal excretion of sodium and water, thereby reducing blood volume. This physiological response helps to counteract the effects of conditions that lead to increased blood volume, making ANP a key player in the body's homeostatic mechanisms for managing cardiovascular health.

The other circumstances described, such as low blood volume or dehydration, will not trigger ANP release since these conditions would lead to opposite physiological responses aimed at conserving fluid and maintaining blood pressure. High blood pressure on its own may not directly trigger ANP unless it is accompanied by an increase in blood volume that distends the atria. Thus, the condition that most clearly initiates ANP release is excess blood volume.