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Growth hormone is essential to normal human growth and development, and its secretion is tightly regulated via a feedback control system involving the hypothalamus, the pituitary gland, and the peripheral tissues. Which of the following is a stimulus for the secretion of growth hormone?

(A) Hypoglycemia
(B) Obesity
(C) Pregnancy
(D) Somatomedin excess
(E) Somatostatin therapy
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(A) Hypoglycemia
In addition to being necessary to normal human growth and development, GH is critical in the stress response to starvation. GH is released in response to hypoglycemia and acts directly to decrease glucose uptake by cells and increase lipolysis, resulting in an increase in blood sugar levels.

Answer B is incorrect. GH secretion is not stimulated by obesity, but rather is reduced by this condition.

Answer C is incorrect. Pregnancy is not a stimulus for GH secretion. Rather, GH secretion decreases in pregnancy.

Answer D is incorrect. Somatomedins, or in- sulin-like growth factors, are secreted by the liver in response to GH and mediate the metabolic changes necessary for growth and development. These intermediaries also act on the hypothalamus and the anterior pituitary via a negative feedback mechanism to reduce GH secretion.

Answer E is incorrect. Somatostatin is not a stimulus for GH secretion but rather is a component of the negative feedback system that regulates GH secretion. Somatostatin is secreted by the hypothalamus in response to stimulation by insulin-like growth factors/somatomedins and acts on the anterior pituitary to reduce GH secretion. Somatostatin may be used clinically to control the diarrhea associated with carcinoid syndrome or VIPomas.