Pituitary Physiology

Question 0

What are 3 categories you can put ant. pit. hormones into based on structure?

Answer 0

Glycoproteins: FSH, LH, and TSH.
Part of large molecule, POMC: ACTH.
…similar structure: GH and PRL.

Question 1

2 genes to remember in pituitary development? What happens in they’re missing?

Answer 1

Prop-1 and Pit-1.

If missing, patient has hypopituitism.

Question 2

Important (but simple): What effect does target endocrine gland hormone secretion have on hormone secretion from the pituitary and hypothalamus?

Answer 2

Target gland hormones provide negative feedback to the hypothalamus and pituitary.

Question 3

So when the target endocrine gland stops working, what happens to the pituitary?

Answer 3

Hyperplasia and hypersecretion of hormones to try to stimulate target gland.

Question 4

What defines a portal system?

Answer 4

Two consecutive capillary beds.

also the capillary bed through which the ant. pit. receives hypothalamic hormones is “quite fenestrated”

Question 5

Two types of secretion rhythms to remember?

Answer 5

Circadian - e.g. cortisol.

Ultradian - pulsatile, eg. GnRH

Question 6

Hypothyroidism caused by thyroid gland destruction would lead to hypertrophy of which gland?

Answer 6

The ant. pit., trying to make more TSH.

Question 7

How is ACTH produced?

Answer 7

As part of a larger molecule, POMC.

Question 8

What else, notably, does POMC contain?

Answer 8

melanotropins, which stimulate skin pigmentation (and lipolysis)

Question 9

Main inhibitor of ACTH release?

Answer 9

Cortisol.

Question 10

When do you measure cortisol levels when trying to see if someone is deficient in it?

Answer 10

In the morning- 8am-ish, when it should be highest.

Question 11

When do you measure cortisol when determining if someone has an excess?

Answer 11

Late at night, when there should be very little. (usually done at home with cheek swab, for convenience)

Question 12

What will cortisol and ACTH levels be like when someone has a cortisol-secreting adrenal tumor?

Answer 12

Cortisol high, ACTH low (due to neg. feedback).

Question 13

You’re studying for a test at 1am (and stressed out about it). What will ACTH and cortisol levels be like?

Answer 13

ACTH and cortisol will both be high.

The point made was that stress can override circadian rhythms.

Question 14

3 ways to increase GH releasing hormone (GHRH)?

Answer 14

Hypoglycemia, dietary protein, exercise.

Question 15

What are 2 factors that the hypothalamus releases in the growth hormone axis?

Answer 15

GHRH - stimulates GH release

Somatostatin - inhibits GH release

Question 16

What is the main source of negative feedback for GH release to the ant. pit. and hypothalamus?

Answer 16

IGF-1

GH only gives negative feedback to the hypothalamus

Question 17

What are 5 things that somatostatin inhibits (the release of?)?

Answer 17

In the pituitary: GH, PRL, and TSH.

In the pancreas: Insulin and glucagon.

Question 18

2 FDA-approved somatostatin analogues?

Answer 18

Octreotide

Lantreotide

Question 19

How do you measure GH levels in a person?

Answer 19

Usually one measures IGF-1, as GH has a short half-life and pulsatile secretion - random measurement wouldn’t reflect actual levels.

Question 20

What’s unusual about feedback in the prolactin axis? What provides suppression?

Answer 20

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.

Question 21

What overrides dopamine inhibition of PRL release?

Answer 21

Prolactin Releasing Factors (PRFs) from the hypothalamus.

Question 22

What are some ways to stimulate PRL release?

Answer 22

Breast stimulation, estrogen, dopamine antagonists, sleep, TRH

Question 23

What regulatory activity does PRL itself have?

Answer 23

Inhibits FSH and LH release. (recall that this causes reduced fertility while nursing, but isn’t an effective form of birth control)

Question 24

3-4 things that provide negative feedback in the Hypothalamic-Pituitary-Gonadal axis?

Answer 24

Testosterone/progesterone
Inhibin
Estrogen

Question 25

Review: What’s the effect of constant infusion of GnRH?

Answer 25

Suppression of FSH and LH release. Recall that that GnRH secretion must be pulsatile to be effective.

Question 26

Review: Why does the peak in E2 precede the peak in LH before ovulation?

Answer 26

E2 switches to having a positive feedback role -> drives spike in LH (and FSH) at ovulation.

Question 27

What do FSH, LH, and estrogen levels look like normal menopause? Why?

Answer 27

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.

Question 28

What extra effect does TRH have at high levels?

Answer 28

TRH at high levels stimulates PRL release.

Question 29

What provides negative feedback to the thyrotropes in the Hypothalamic-Pituitary-Thyroid axis? How?

Answer 29

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.)