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QUESTIONS

DIRECTIONS: Choose the one best response to each question.

Production of which of the following hormones would be most impaired by lesions that affect the pituitary stalk or hypothalamus?

A. Adrenocorticotrophic hormone

B. Growth hormone

C. Oxytocin

D. Prolactin

E. Thyroid-stimulating hormone

The answer is C. (Chap. 371) The pituitary gland weighs ~600 mg and is located within the sella turcica ventral to the diaphragma sella; it consists of anatomically and functionally distinct anterior and posterior lobes. The bony sella is contiguous to vascular and neurologic structures, including the cavernous sinuses, cranial nerves, and optic chiasm (Figure IX-1). Thus, expanding intrasellar pathologic processes may have significant central mass effects in addition to the endocrinologic impact. The posterior pituitary is supplied by the inferior hypophyseal arteries. In contrast to the anterior pituitary, the posterior lobe is directly innervated by hypothalamic neurons (supraopticohypophyseal and tuberohypophyseal nerve tracts) via the pituitary stalk. Thus, posterior pituitary production of vasopressin (antidiuretic hormone) and oxytocin is particularly sensitive to neuronal damage by lesions that affect the pituitary stalk or hypothalamus.

FIGURE IX-1

Diagram of hypothalamic-pituitary vasculature. The hypothalamic nuclei produce hormones that traverse the portal system and impinge on anterior pituitary cells to regulate pituitary hormone secretion. Posterior pituitary hormones are derived from direct neural extensions.

During lactation, increased levels of prolactin hormone result in all of the following EXCEPT:

A. Anovulation

B. Decreased levels of estrogen

C. Increased gonadal steroidogenesis

D. Shortened luteal phase of menstrual cycle

E. Suppressed gonadotrophin-releasing hormone levels

The answer is C. (Chap. 371) Prolactin (PRL) acts to induce and maintain lactation, decrease reproductive function, and suppress sexual drive. These functions are geared toward ensuring that maternal lactation is sustained and not interrupted by pregnancy. PRL inhibits reproductive function by suppressing hypothalamic gonadotropin-releasing hormone and pituitary gonadotropin secretion and by impairing gonadal steroidogenesis in both women and men. In the ovary, PRL blocks folliculogenesis and inhibits granulosa cell aromatase activity, leading to hypoestrogenism and anovulation. PRL also has a luteolytic effect, generating a shortened, or inadequate, luteal phase of the menstrual cycle.

A 45-year-old man reports to his primary care physician that his wife has noted coarsening of his facial features over several years. In addition, he reports low libido ...

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