Endocrine regulation · USMLE Step 1

Which of the following endocrine regulation scenarios illustrates a ‘short-loop’ negative feedback mechanism?

  1. Thyroid hormone inhibiting hypothalamic TRH release
  2. Cortisol inhibiting both CRH and ACTH release
  3. Pituitary hormone inhibiting hypothalamic releasing hormone secretion
  4. Pancreatic insulin inhibiting glucagon secretion
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Correct answer: Pituitary hormone inhibiting hypothalamic releasing hormone secretion

Short-loop negative feedback refers to a pituitary hormone acting back on the hypothalamus to inhibit secretion of its releasing hormone — matching 'pituitary hormone inhibiting hypothalamic releasing hormone secretion.' Thyroid hormone or cortisol inhibiting the hypothalamus/pituitary are long-loop feedback, and insulin inhibiting glucagon is local paracrine regulation within the pancreas, not a short-loop axis mechanism.

Difficulty: Medium Question 15 of 23

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