The endocrine glands react to demands for increased hormone production by an increase in their functional size and their weight. Thus, the thyroid, the adrenal, and the parathyroid glands are known to enlarge demonstrably in the syndromes associated with their increased hormone production. The pituitary, too, is generally considered to react in this manner, and increased pituitary size has been reported, for example, in primary myxedema and following adrenalectomy for Cushing's syndrome: in both instances there is presumably a compensatory increase in tropic hormone output by the pituitary—thyroid stimulating hormone in the first, adrenocorticotrophic hormone in the second. Evidence of a correlation between decreasing size and reduced hormone output can be seen in steroid-treated patients where a diminution in pituitary size—associated with decreased tropic hormone release—may well be the rule.
These examples of reactive changes in pituitary size and weight in the human could be challenged; pituitary size increase in
Fand SB, Ehmann CW, Buscaglia AJ, Messineo L. Nuclear Studies in Human Pituitary Glands of Varying Weights. JAMA. 1967;199(8):563–566. doi:10.1001/jama.1967.03120080097017
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