Chemistry Practice Question

During a workup to rule out secondary causes of hypertension, a 51 year old male is found to have a normal CBC and chemistry panels, and elevated aldosterone and renin levels. The causative lesion is most likely located in which of the following locations?

Show Answer and Explanations

Renal artery — Correct answer

Correct. The patient has secondary hyperaldosteronism. Restricted blood flow to the kidney, such as from atherosclerotic plaque deposition in the renal artery, or from fibromuscular hyperplasia, causes increased renin secretion from the juxtaglomerular apparatus. Juxtaglomerular apparatus tumors can also release renin. Renin converts angiotensinogen to angiotensin I, and ACE in the lungs converts angiotensin I to angiotensin II, which increases the blood pressure by vasoconstriction and increases aldosterone secretion from the adrenal cortex.

Adrenal cortex.

Incorrect. Aldosterone is secreted from the adrenal cortex (predominantly the zona glomerulosa - from outside to inside the layers of the cortex are "GFR" - zona glomerulosa, zona fasciculata, zona reticularis). Primary hyperaldosteronism is caused by adrenal lesions such as adrenal hyperplasia or an adrenal adenoma. The aldosterone will be high, and the renin level will be low.

Pituitary

Incorrect. Hypernatremia, hypovolemia and the renin-angiotensin system stimulate the posterior pituitary to release ADH, which upregulates aquaporins in the renal tubules to conserve free water. This is not generally a cause of hypertension, and excess ADH would cause hyponatremia.

Brainstem

Incorrect. The brainstem contains most of the structures which increase fluid intake by stimulating thirst. A lesion here would not result in the findings in the question stem.

Duodenum

Incorrect. A duodenal lesion would not result in the findings in the question stem.

Summary