Pituitary Physiology Flashcards
What are 3 categories you can put ant. pit. hormones into based on structure?
Glycoproteins: FSH, LH, and TSH.
Part of large molecule, POMC: ACTH.
…similar structure: GH and PRL.
2 genes to remember in pituitary development? What happens in they’re missing?
Prop-1 and Pit-1.
If missing, patient has hypopituitism.
Important (but simple): What effect does target endocrine gland hormone secretion have on hormone secretion from the pituitary and hypothalamus?
Target gland hormones provide negative feedback to the hypothalamus and pituitary.
So when the target endocrine gland stops working, what happens to the pituitary?
Hyperplasia and hypersecretion of hormones to try to stimulate target gland.
What defines a portal system?
Two consecutive capillary beds.
also the capillary bed through which the ant. pit. receives hypothalamic hormones is “quite fenestrated”
Two types of secretion rhythms to remember?
Circadian - e.g. cortisol.
Ultradian - pulsatile, eg. GnRH
Hypothyroidism caused by thyroid gland destruction would lead to hypertrophy of which gland?
The ant. pit., trying to make more TSH.
How is ACTH produced?
As part of a larger molecule, POMC.
What else, notably, does POMC contain?
melanotropins, which stimulate skin pigmentation (and lipolysis)
Main inhibitor of ACTH release?
Cortisol.
When do you measure cortisol levels when trying to see if someone is deficient in it?
In the morning- 8am-ish, when it should be highest.
When do you measure cortisol when determining if someone has an excess?
Late at night, when there should be very little. (usually done at home with cheek swab, for convenience)
What will cortisol and ACTH levels be like when someone has a cortisol-secreting adrenal tumor?
Cortisol high, ACTH low (due to neg. feedback).
You’re studying for a test at 1am (and stressed out about it). What will ACTH and cortisol levels be like?
ACTH and cortisol will both be high.
The point made was that stress can override circadian rhythms.
3 ways to increase GH releasing hormone (GHRH)?
Hypoglycemia, dietary protein, exercise.
What are 2 factors that the hypothalamus releases in the growth hormone axis?
GHRH - stimulates GH release
Somatostatin - inhibits GH release
What is the main source of negative feedback for GH release to the ant. pit. and hypothalamus?
IGF-1
GH only gives negative feedback to the hypothalamus
What are 5 things that somatostatin inhibits (the release of?)?
In the pituitary: GH, PRL, and TSH.
In the pancreas: Insulin and glucagon.
2 FDA-approved somatostatin analogues?
Octreotide
Lantreotide
How do you measure GH levels in a person?
Usually one measures IGF-1, as GH has a short half-life and pulsatile secretion - random measurement wouldn’t reflect actual levels.
What’s unusual about feedback in the prolactin axis? What provides suppression?
The end product (milk) doesn’t provide negative feedback.
PRL is suppressed by dopamine from the hypothalamus.
Note that this is the one axis where the hypothalamus inhibits secretion instead of stimulating it.
What overrides dopamine inhibition of PRL release?
Prolactin Releasing Factors (PRFs) from the hypothalamus.
What are some ways to stimulate PRL release?
Breast stimulation, estrogen, dopamine antagonists, sleep, TRH
What regulatory activity does PRL itself have?
Inhibits FSH and LH release. (recall that this causes reduced fertility while nursing, but isn’t an effective form of birth control)
3-4 things that provide negative feedback in the Hypothalamic-Pituitary-Gonadal axis?
Testosterone/progesterone
Inhibin
Estrogen
Review: What’s the effect of constant infusion of GnRH?
Suppression of FSH and LH release. Recall that that GnRH secretion must be pulsatile to be effective.
Review: Why does the peak in E2 precede the peak in LH before ovulation?
E2 switches to having a positive feedback role -> drives spike in LH (and FSH) at ovulation.
What do FSH, LH, and estrogen levels look like normal menopause? Why?
FSH and LH are high, estrogen is low.
This is because menopause is ovarian “failure” (how about “retirement”?), not a change in pituitary/hypothalamus function.
What extra effect does TRH have at high levels?
TRH at high levels stimulates PRL release.
What provides negative feedback to the thyrotropes in the Hypothalamic-Pituitary-Thyroid axis? How?
T3, mainly, by downregulating TRH receptors on thyrotropes in the ant. pit., leading to less TSH release.
(Somatostatin from hypothalamus also is inhibitory. And the arrows suggest T3/T4 also provide neg. feedback to the hypothal.)
