Final answer:
The hormone ANP is secreted from the atria of the heart when increased blood volume causes these chambers to stretch. It promotes the excretion of sodium and water through the kidneys and inhibits renin and aldosterone, thereby decreasing blood volume and pressure.
Step-by-step explanation:
The hormone ANP is secreted from the atria as increasing blood volume stretches this chamber. The heart possesses endocrine cells in the walls of the atria that specifically respond to increased blood volume by releasing the hormone atrial natriuretic peptide (ANP).
ANP acts on the kidneys to facilitate the excretion of sodium (Na+) and water, which leads to a reduction in blood volume and pressure. It also inhibits the secretion of renin and aldosterone, which further helps in reducing fluid retention in the body. The atrial cells produce ANP when they are stretched due to an increase in blood volume, signaling the kidneys to aid in balancing fluid levels and maintaining healthy blood pressure.