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Which mechanism primarily controls the secretion of pituitary hormones?

A.

Positive feedback from the adrenal medulla.

B.

Direct nerve impulses from the thalamus.

C.

Negative feedback from target organs.

D.

Blood pressure levels.

Answer and Explanation

The Correct Answer is C

A. Positive feedback from the adrenal medulla.: The adrenal medulla releases catecholamines (epinephrine/norepinephrine) and does not provide the primary control mechanism for pituitary hormone secretion.
B. Direct nerve impulses from the thalamus.: The thalamus is a relay station for sensory information and does not directly send the neural signals that regulate pituitary hormone release.
C. Negative feedback from target organs.: Target-organ hormones (e.g., cortisol, thyroid hormones, sex steroids) feed back to the hypothalamus and pituitary to decrease releasing/trophic hormone secretion, which is the principal control mechanism.
D. Blood pressure levels.: Blood pressure can influence certain endocrine responses (e.g., via RAAS) but is not the primary mechanism controlling overall pituitary hormone secretion.


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Related Questions

Correct Answer is D

Explanation

A. It directly releases cortisol into the bloodstream.:The hypothalamus does not release cortisol; cortisol is secreted by the adrenal cortex under pituitary control.
B. It secretes antidiuretic hormone (ADH) to control fluid balance.:ADH is synthesized in the hypothalamus but is stored and released from the posterior pituitary; secretion of ADH is one hypothalamic function but not the primary role in the HPA axis.
C. It inhibits the release of aldosterone from the adrenal cortex.:Aldosterone regulation is mainly via the renin–angiotensin system and potassium levels; the hypothalamus does not primarily inhibit aldosterone.
D. It secretes corticotropin-releasing hormone (CRH) to stimulate ACTH release.:The hypothalamus releases CRH, which stimulates the anterior pituitary to secrete ACTH, initiating the HPA axis cascade that leads to cortisol production.

Correct Answer is C

Explanation

A. To increase blood glucose levels directly:The hypothalamus does not directly raise blood glucose; it regulates hormones that influence this process indirectly via other glands.
B. To store and release oxytocin:Oxytocin is stored and released by the posterior pituitary, not the hypothalamus itself.
C. To secrete corticotropin-releasing hormone (CRH):The hypothalamus produces and releases CRH, which stimulates the anterior pituitary to secrete ACTH, initiating the HPA axis cascade leading to cortisol release.
D. To produce aldosterone:Aldosterone is a mineralocorticoid hormone produced by the adrenal cortex, not by the hypothalamus.

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