What is the function of ANP in the body?

Atrial natriuretic peptide (ANP) plays a critical role in regulating blood pressure and fluid balance in the body. When the heart's atria are stretched due to increased blood volume, ANP is released as a response. This peptide acts primarily to reduce blood pressure and blood volume through several mechanisms.

Firstly, ANP promotes natriuresis, which is the excretion of sodium in the urine. By encouraging the kidneys to eliminate sodium, water follows due to osmosis, leading to a decrease in blood volume. A reduction in blood volume consequently lowers blood pressure.

Additionally, ANP helps to inhibit the renin-angiotensin-aldosterone system (RAAS), a hormonal system that usually promotes sodium retention and vasoconstriction. By counteracting the effects of this system, ANP effectively contributes to the regulation of blood pressure.

In summary, the primary function of ANP in the body is to reduce blood pressure and blood volume, making this the correct answer.