Lecture 13: Pituitary Physiology Flashcards
What are the two enzymes involved in adenohypophysis development that we need to remember?
Prop 1 and Pit-1
What is Prop 1?
One of the enzymes that is involved embryological development of the anterior pituitary
Precursor to Pit-1 and eventually forms the “tropes” of the anterior pituitary
What is Pit-1?
One of the enzymes that is involved embryological development of the anterior pituitary
A produce ot prop 1 and forms “tropes” of anterior pituitary
A mutation in Prop 1 will lead to decreased production of which pituitary hormone?
LH, FSH, FSH, PRL and TSH
Good kush and alcohol
What are the 3 groups of anterior pituitary hormones?
- Glycoprotein hormones (TSH, LH, FSH)
- ACTH
- from large molecule POMC
- Growth hormone and prolactin
- structural homology
- both can activate prolactin receptor
What is the function of GH?
Stimulates secretion of IGF-1 from lliver and other organs which is responsible for GH’s anabolic effects. Stimulates lipid and CHO metabolism
What is POMC?
Pro-opiomelanocortin
Cleaved to form ACTH
Which hormones share same alpha subunit in structure?
TSH, LH, FSH
What stimulates CRH?
- physical stress
- emotional stress
- hypoglycemia
- cold exposure
- pain
What is the hallmark of feedback regulation for adenohypophysis?
The secretion of hormones from target glands will suppress the release of pituitary and hypothalamic hormones
Negative feedback
What happens when you lose feedback inhibition?
Clinically, loss of feedback inhibition by target hormones results in pituitary trophic hormone hypersecretion and HYPERPLASIA of pituitary cells as seen in severe hypothyroidism or hypoadrenalis
What is a ultradian rhythm?
Bursts (spikes, pulses) of hormone secretion
Can be superimposed on circadian rhythms
Seen in reproduction
Hypothyroidism caused by thyroid gland destruction can lead to hypertrophy of which gland?
Anterior pituitary gland
If you lose organ, then you get anterior pituitary hypertrophy
What laboratory picture is expected in a patient with excessive cortisol production by an adrenal tumor?
Cortisol high ACTH low
Why is CRH not mentioned?
Because it is not measured
Most of it gets taken up in portal system
If you are measuring cortisol insufficiency, when do you measure cortisol?
Measure cortisol when it is supposed to be HIGHEST
If you are measuring hypercortisolemia, when do you measure cortisol?
Measure cortisol when it is supposed to be LOWEST
Student is studying for a test at 1am. What is his cortisol profile at this time?
Cortisol high, ACTH high
The same student is asleep at 1 am the following night. What is cortisol profile?
ACTH low cortisol low
What is GHRH inhibited by?
GH and IGF1
What is GHRH stimulated by?
- hypoglycemia
ii. exercise
iii. dietary protein
Which physiologic process will lead to decrease in GH production?
- Reduction in GHRH secretion
- Increase in somatostatin (negative feedback)
- Increase in IGF-1 (negative feedback)
What are the key characteristics of somatostatin?
- opposes GHRH action by inhibiting GH
- receptors in hypothalamus, GI tract, pancreas
- inhibits TSH and prolactin in pituitary
- inhibits glucagon and insulin in pancreas
- Octreotide and lantreotide are approved analogs of somatostatin
What does somatostatin inhibit in anterior pituitary?
- GH
- TSH
- Prolactin
You suspect excessive production of growth hormone. What laboratory measurement will you order first?
IGF-1
You CANNOT read the serum of GH
NEVER CHECK GH
What is the effect of dopamine on prolactin?
Dopamine INHIBITS prolactin
What is the effect of estrogen on prolactin?
Estrogen stimulates prolactotrophes
What is the only example of positive feedback in the HP-hormone Axis?
GnRH, FSH, LH and estrogen (estrogen is both stimulatory and inhibitory)
What is the effect of prolactin on the gonadal axis?
Negatively regulates secretion of LH and FSH
What is different about the prolactin axis?
It is under constant INHIBITION from the hypothalamus in the form of dopamine
Only when there is suckling or estrogen does the hypothalamus send out prolactin releasing factors
What physiologic process can explain amonorrhea in a nursing woman?
High prolactin negatively regulates HPG axis
Why do we treat prolactinemia in men?
To encourage gonadal growth
What does pulsatile infusion of GnRH do?
Stimulates LH and FSH secretion
What does constant infusion of GnRH do?
Inhibits LH and FSH
What lab picture is characteristic of physiologic menopause?
Estrogen low, LH and FSH high
What lab changes are expected in case of excessive thyroid hormone production?
Thyroxine high, TSH low
What does hormone activity depend on?
Hormone activity depends on both the quantity present, and its mode of release (pulsatile vs. constant)
-remember when ordering laboratory test
