Which two hormones are central to the classical RAAS pathway?

• A. Adrenaline and noradrenaline
• B. Antidiuretic hormone and renin
• C. Angiotensin II and aldosterone
• D. Calcitonin and parathyroid hormone

Answer: (C)

The key idea is the action sequence of the RAAS, where two main hormonal signals drive the response to low blood pressure or low blood volume: angiotensin II and aldosterone. When blood pressure drops, renin is released and starts a cascade that converts angiotensinogen to angiotensin I, which is then turned into angiotensin II. Angiotensin II has direct effects to raise pressure by constricting blood vessels and by prompting the adrenal cortex to release aldosterone. Aldosterone, in turn, acts on the kidneys to reabsorb sodium (and with it water), increasing blood volume and pressure. Together, angiotensin II and aldosterone are the principal effectors that restore balance in the classical RAAS pathway. Renin is essential as the initiator, but it’s an enzyme, not a hormone, so the core hormonal duo is angiotensin II and aldosterone.