If the kidneys sense reduced renal blood flow, as can happen with reduced blood pressure, they secrete renin into the blood, where it reacts with angiotensinogen to produce angiotensin I, which is converted to angiotensin II by angiotensin converting enzyme (ACE). Both angiotensin I and II are vasoconstrictors. Angiotensin II additionally leads to the production of aldosterone by the adrenal cortex, which in turn leads to an increase in blood volume.