Which process is a function of the kidney hormones? (Renin-angiotensin system)

• A. Prostaglandin increases blood flow and vascular permeability.
• B. Bradykinin regulates intrarenal blood flow via vasodilation or vasoconstriction.
• C. Renin raises blood pressure because of angiotensin and aldosterone secretion.
• D. Erythropoietin promotes calcium absorption in the gastrointestinal tract.

Answer: (C)

The key idea here is how kidney hormones regulate blood pressure through the renin-angiotensin system. When the kidneys sense low blood pressure or low sodium delivery, they release renin. Renin starts a cascade: it converts angiotensinogen to angiotensin I, which is turned into angiotensin II. Angiotensin II is a strong vasoconstrictor and also stimulates aldosterone release from the adrenal cortex. Aldosterone promotes sodium (and water) reabsorption in the distal nephron, increasing blood volume and pressure. So renin raises blood pressure by kickstarting angiotensin II and aldosterone actions, which is exactly what the statement conveys.

Other listed substances play different roles (prostaglandins modulate renal blood flow, bradykinin affects intrarenal flow but isn’t the main hormonal driver of this BP pathway, and erythropoietin mainly stimulates red blood cell production rather than calcium absorption in the gut).