Pituitary Physiology (5/15) Flashcards Preview

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Flashcards in Pituitary Physiology (5/15) Deck (60):
1

Describe post pit development

The posterior pituitary (neurohypophysis) develops as an evagination of the ventral hypothalamus. From neural crest cells.

2

Describe ant pit dev

The anterior pituitary (adenohypophysis) is formed from evagination of pharyngeal ectoderm, which initially forms a duct called Rathke’s pouch and later fills in and closes. Develops over weeks 5-20

3

What TFs guide cellular differentiation during dev

Transcription factors that guide this process include Prop-1 and Pit-1. Inactivating mutations in these transcription factors will cause deficiencies in pituitary hormones.

4

List the 5 ant pit cell types

1. Somatotrope
2. Thyrotrope
3. Lactotrope
4. Gonadotrope
5. Corticotrope

5

What does somatotrope produce?

Growth hormone (GH)

6

What does thryrotrope produce?

Thyrotropin (TSH)

7

What does lactotrope produce?

Prolactin (PRL)

8

What does gonadotrope produce?

LH and FSH

9

What does corticotrope produce?

Adrenocorticotropin (ACTH)

10

What are the 3 main groups of ant pit hormones?

1. Glycoprotein hormones (TSH, LH, FSH, share alpha unit)

2. ACTH (comes from POMC)

3. GH and Prolactin (struc homology, can both activate prolactin receptor)

11

What does LH do?

Stimulates production and secretion of testosterone, preps uterus for implantation of fertilized ovum, stimulates ovulation

12

What does FSH do?

Stimulates egg and sperm production, stim estrogen synthesis

13

What does TSH do?

Stim secretion of thyroid hormones by thyroid gland and regulates thyroid cell proliferation and survival

14

What does ACTH do?

Stim synthesis and secretion of cortisol/adrenal cortex steroids by cortex of adrenal gland and proliferation and survival of adrenal cortex cells

No ACTH: atrophic adrenals
XS ACTH: hypertrophic adrenals

15

What does prolactin do?

Initiates milk production

16

What does human growth hormone do?

Stim growth and other effects post natally. Stimulates secretion of IGF-1 from the liver and other organs which is responsible for GH's anabolic effects. Stimulates lipid and CHO metabolism

17

Which hormones have the same alpha subunit?

TSH, LH, FSH

18

What does loss of feedback regulation cause?

Pituitary trophic hormone hypersec and hyperplasia of pit cells like in severe hypothyroidism or hypoadrenalism

19

How do hypothalamic hormones get to the anterior pituitary?

Via the hypothalamic-pituitary portal system

Note: the portal system has two consecutive capillary beds. First carries hormones to the ant pit and does not reach the systemic circulation. Second carries hormones away from the ant pit and reaches systemic circulation

20

What are two rhythms in endocrinology?

Circadian (daily), most common

Ultradian (bursts, like GnRH)

21

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

Anterior pituitary...loss of negative feedback regulation

22

Describe CRH/ACTH system

Hypothal-->CRH (neg to hypothal)-->ant pit-->ACTH (neg on ant pit and hypothal)-->adrenal gland-->Cortisol (neg on ant pit and hypothal)

23

What are the extraadrenal actions of ACTH?

Stimulate lipolysis and inc skin pigmentation

24

What stimulates ACTH release?

CRH, stress, hypoglycemia, anxiety, depression, alpha and beta adrenergic agonists

25

What pattern does ACTH get released normally?

Diurnal: peaks just before awakening with pulsatility

26

What inhibits ACTH?

Cortisol

27

To look for a deficiency in ACTH, when would you measure it?

Highest in the morning normally, measure then to see if its low

28

To look for excess in ACTH, when would you measure it?

Lowest at night normally, measure to see if its high

29

How do we measure hypothalamic hormones in the blood?

We don't ! It doesn't get to the systemic circulation

30

Someone wakes up stressed at 1am, what is their cortisol profile?

High ACTH and cortisol

31

Someone is sleeping at 1am, what is their cortisol profile?

Lower ACTH and Cortisol

32

Describe the growth hormone feedback loop

Hypothal-->GHRH (inhib hypothal) and Somatostatin (inhibits ant pit and hypothal)-->ant pit-->GH-->Liver-->IGF1 (inhibits ant pit and hypothal)

33

What is GHRH

Stimulatory hypothalamic hormone that is stim for somatotropes

34

What kind of rhythm is GHRH released in?

Episodic

35

What is GHRH release stimulated by/

Hypoglycemia, dietary protein, exercise

36

What is GHRH inhibited by?

IGF1 and GH

37

Is somatostatin confined to ant pit?

No also has receptors elsewhere like GI and pancreas, hypothalamus

38

What does somatostatin do?

Opposes GHRH action-inhibits GH release. Also inhibits TSH, PRL in pit and glucagon/insulin in panc

39

What somatostatin analogs are FDA approved?

Octreotide and Lantreotide

40

What is GH's rhythm and half life?

Pulatilie with a short half life of 6-20 min

41

What regulates the amplitude and freq of GH release

Age, gender, nutrition, sleep, body composition, stress, exercise

42

What does GH stimulate and how?

Stimulates post natal growth via indirect effects of IGF1

43

If you suspect excessive production of GH. What lab measurement would you order 1st

IGF1

44

What physiologic process will lead to decrease in GH production?

-reduction in GHRH secretion
-Inc in somatostatin
-Inc in IGF1

45

What inhibits prolactin?

Dopamine and dopamine agonists

46

Waht does prolactin do?

Negatively regulates LH and FSH via hypothalamus (GnRH) and stimulates milk production

47

Describe the prolactin axis

Hypothal-->PRFs, dopamine (neg to ant pit)-->ant pit-->Prl (neg to hypothal)-->mammary gland

Also stimulating to ant pit is E2 from the ovary

Neural stimulus also goes from mammary gland to hypothalamus

48

What hormone does prolactin stimulate?

NONE, does not stimulate a hormone and not a subject to feedback

49

What stimulates prolactin?

Breast stimulation, stress, estrogen, sleep, dopamine antag, TRH

50

Where is prolactin secreted from?

Lactotropes

51

What physiologic process can explain amenorrhea in a nursing woman?

High prolactin negatively regulates hypothalamic pituitary gonadal axis

52

What is more impt the concentration or pulsatility of GnRH?

Pulsatility and pulse freq are critical with greater freq and amplitude in puberty

Pulsatile infusion stim LH and FSH sec

Constant infusion inhibits LH and FSH sec to suppress gonadal fxn

53

What does high FSH, high LH, and low estrogen signal?

Menopause

54

What does TRH do?

Stim release of TSH and prolactin

55

What does TSH do?

TSH stimulates the conversion of T4-->T3. Responsive to intracellular T3 levels, when T3 is high, TRH receptors dec and thus response of thyrotrope to TRH decreases and thus TSH decreases

56

Describe the thyroid axis

Hypothal--> somatostatin (neg to ant pit) and TRH-->Ant pit-->TSH--->T4->T3 (neg regulate ant pit and hypothal)

57

What lab changes are expected when there is excessive production of TH (thyroxin) by overactive thyroid gland?

Low TSH, high thyroxin

58

What is the only axis in which the hypothalamus is primarily inhibitory?

Prolactin regulation by hypothalamus is primarily inhibitory

59

What are the two inhibitory hypothalamic factors?

Somatostatin and dopamine

60

Hormone activity depends on what?

quantity present and mode of release (impt for lab tests)