The kidney does this by secreting the proteolytic enzyme renin . Renin acts on angiotensinogen , a plasma protein, splitting off a fragment containing 10 amino acids called angiotensin I . I producing the octapeptide angiotensin II . Angiotensin II Constricts the walls of arterioles closing down capillary beds. Stimulates the adrenal cortex to release aldosterone .
Aldosterone causes the kidneys to reclaim more sodium and thus water.
Increases the strength of the heartbeat. All of these actions lead to an increase in blood pressure . The Heart A rise in blood pressure stretches the atria of the heart. ANP is a peptide of 28 amino acids. The net effect of these actions is to reduce blood pressure by reducing the volume of blood volume in the system.