MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
An individual sustains a severe injury that results in significant blood loss. In response to the decreased blood volume and pressure, the kidneys release a hormone that initiates a cascade of events to restore blood pressure and fluid balance. Which hormone is primarily released by the kidneys in this immediate response?
- AAldosterone
- BAngiotensin II
- CRenin
- DAntidiuretic Hormone (ADH)
Show answer & explanationAnswer & explanation
Correct answer: C. Renin
In response to decreased blood pressure and volume, the juxtaglomerular cells in the kidneys release renin. Renin then initiates the renin-angiotensin-aldosterone system (RAAS) which ultimately leads to increased blood pressure and fluid retention.
Why the other options are wrong
- A. Aldosterone is released by the adrenal cortex later in the RAAS pathway, stimulated by Angiotensin II, not directly by the kidney in the initial response.
- B. Angiotensin II is a powerful vasoconstrictor and stimulant for aldosterone release, but it is produced from angiotensinogen by the action of renin and ACE, not directly released by the kidney.
- D. ADH is released by the posterior pituitary in response to increased plasma osmolarity or significant blood volume decrease, but renin is the primary initial hormone from the kidney in this cascade.
Renin-Angiotensin-Aldosterone System (RAAS)
A hormone system that regulates blood pressure and fluid balance. When blood pressure or volume drops, the kidneys release renin, which initiates a cascade leading to the production of Angiotensin II and Aldosterone.
- Renin is released by kidney juxtaglomerular cells.
- Renin converts angiotensinogen to Angiotensin I.
- ACE converts Angiotensin I to Angiotensin II.
- Angiotensin II causes vasoconstriction and Aldosterone release.
- Aldosterone promotes Na+ and water reabsorption in kidneys.
Memory trick: Renin Rushes: When blood pressure drops, Renin Rushes out of the kidney!