Hypothalamic–Pituitary Control
Key facts on anterior and posterior pituitary hormones, their hypothalamic control, and target organ effects.
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Questions Covered in This Set
11 cards to master
Embryologic origin of the anterior pituitary (adenohypophysis)?
Rathke's pouch — an upward invagination of oral ectoderm; it is glandular epithelium that synthesizes its own hormones.
How does the hypothalamus communicate with the anterior pituitary?
Chemically, via the hypothalamo-hypophyseal portal system — two capillary beds in series delivering releasing/inhibiting factors at high local concentration.
What happens to pituitary hormones after stalk section?
All anterior pituitary hormones fall EXCEPT prolactin, which rises, because its dominant hypothalamic signal (dopamine) is inhibitory.
What is the posterior pituitary, structurally?
Neural tissue (downgrowth of diencephalon) — axon terminals of magnocellular neurons from the supraoptic and paraventricular nuclei; it stores but synthesizes nothing.
Name the three families of anterior pituitary hormones.
Glycoprotein (TSH, LH, FSH), somatomammotropin (GH, prolactin), and POMC-derived (ACTH).
Why can very high hCG (molar pregnancy) cause hyperthyroidism?
Glycoprotein hormones share an identical α-subunit; hCG cross-reacts with the TSH receptor since only the β-subunit confers specificity.
Why must GnRH be secreted in pulses?
Pulses every 60–90 min drive LH/FSH; continuous GnRH agonist exposure downregulates receptors and suppresses the gonads (basis of leuprolide therapy).
Why does Addison's disease cause skin hyperpigmentation?
Massive ACTH/POMC output produces MSH-related fragments that stimulate melanocytes.
Contrast direct vs indirect (IGF-1) effects of growth hormone.
Direct: anti-insulin/diabetogenic — lipolysis, decreased glucose uptake, increased hepatic glucose output. Indirect via hepatic IGF-1: chondrocyte proliferation, protein synthesis, positive nitrogen balance.
When is GH secretion greatest, and what stimulates/suppresses it?
Largest pulses during slow-wave sleep; stimulated by hypoglycemia, exercise, ghrelin, GHRH; suppressed by hyperglycemia, free fatty acids, somatostatin.
Why can primary hypothyroidism cause galactorrhea and amenorrhea?
Elevated TRH stimulates prolactin release as well as TSH.
