Q. What is an evolutionary explanatory hypothesis for the secretion by the heart of a hormone that regulates the renal function? Which is that hormone?

The renal regulator hormone secreted by the heart is the atrial natriuretic factor or ANF. The ANF increases the excretion of sodium in the nephron tubules causing less resorption of water more urinary volume and thus lowering the blood pressure. The atrial natriuretic factor is secreted when there is a raise of the length of the heart muscle fibers in response to high blood pressure. The ANF is a natural antihypertensive substance since the health of the heart depends largely upon the stability of the normal blood pressure the evolution should have preserved the atrial natriuretic factor to allow information from the heart to be an additional mechanism for the renal control of the blood pressure.