H2 - Hypothalamic control of Pit Gland

Question 1

Hypothalamo-hypohyseal portal system

- describe the connection between neurohormones and the anterior lobe

Answer 1

1. Blood enters the median eminence thru the superior hypophyseal arteries
   (capillary plexus #1)
2. Nerve terminals of hypothalmic n. terminate @ cap plexus
   - their neurohormones are released into capillary bed
3. Neurohormones are then transported via portal system to 2nd capillary plexus in anterior lobe

Question 2

Why is it important that the plexus in the anterior pit has an easy access to the released hypothalamic hormones?

Answer 2

1. Anterior Pit lies outside the BBB
2. Hormones secreted by the hypothalamic neurons reach the anterior lobe relatively undiluted and at higher [ ] than if they were released into general circulation
3. Hypothalamic hormones act on a local rather than distant target

(If portal sys is severed or AP is transplanted elsewhere, secretion of AP hormones will no longer be subject to nl hypothalamic control.)

Question 3

Are hypothalamic hormones peptides, catecholamines or steroids?
- exceptions?

Answer 3

Peptides

- except DA (catecholamine)

Question 4

Name what these Hypothalamic Hs are associated with in the Ant Pit.

• Thyrotropin releasing H (TRH)
• Gonadotropin releasing H (GnRH)
• Corticotropin releasing H (CRH)

Answer 4

Thyrotropin releasing H (TRH)
↑ TSH, ↑PRL

Gonadotropin releasing H (GnRH)
↑LH, ↑FSH

Corticotropin releasing H (CRH)
↑POMC, ↑ACTH

Question 5

Name what these Hypothalamic Hs are associated with in the Ant Pit.

Growth Hormone releasing H (GHRH)

Somatostatin (GH inhibiting H, GIH)

Prolactin inhibiting factor (PIH)

Answer 5

Growth Hormone releasing H (GHRH)
↑GH

Somatostatin (GH inhibiting H, GIH)
↓GH, ↓ TSH

Prolactin inhibiting factor (PIH)
↓PRL

Question 6

What Hypothalamic H stimulates and what inhibits GH secretion

Answer 6

Growth hormone releasing factor (GHRH)
- stimulates

Somatostatin (GIH)
- inhibits

Question 7

Just as for NT release, hormone secretion from hypothalamic neurons is ______

Answer 7

Ca2+ dependent

*appropriate stim of hypothalamic neuron → AP → Ca2+ entry via VGCC → hormone release from sec. vesicles

Question 8

Gs
Gi
Gq

Answer 8

Gs and Gi both act on Adenylyl cyclase
- Gs → AC → Converts ATP to cAMP → PKA → ↑ Ca2+ (heart

Gq acts on PLC
→ converts PIP2 to IP3 + DAG
- IP3 → ↑ [Ca2+] sm contraction
- DAG → PKC

Question 9

Which endocrine hormones act via cAMP signaling pathway (Gs, Gi)?

Answer 9

FLAT ChAMP (321)

FSH
LH
ACTH
TSH
CRH
hCG
ADH
MSH
PTH

Calcitonin
Glucagon
GHRH

Question 10

Which endocrine hormones act via IP3 (Gq)

Answer 10

GOAT HAG (321)

GnRH
Oxytocin
ADH
TRH
Histamine
Angiotensin II
Gastrin

Question 11

What secretory cells do these hypothalamic neurons act on in the ANTERIOR pituitary?
TRH
GnRH
GHRH
Somatostatin
CRH
PIH (DA)
PRF (TRH)

Answer 11

TRH → thyrotroph

GnRH → gonadotroph

GHRH → somatotroph

Somatostatin →somatotroph

CRH → corticotroph

PIH (DA) → lactotroph

PRF (TRH) → lactotroph

Question 12

Describe what happens to Ant. Pituitary H:
TRH → thyrotroph

GnRH → gonadotroph

GHRH → somatotroph

Somatostatin →somatotroph

CRH → corticotroph

PIH (DA) → lactotroph

PRF (TRH) → lactotroph

Answer 12

TRH → thyrotroph → ↑TSH

GnRH → gonadotroph → ↑LH + FSH

GHRH → somatotroph → ↑ GH

Somatostatin → somatotroph → ↓GH

CRH → corticotroph → ↑ACTH

PIH (DA) → lactotroph → ↓PRL

PRF (TRH) → lactotroph → ↑PRL

Question 13

What hormone is a POMC derivative?

Answer 13

ACTH

too much ACTH + MSH (byproduct) can cause hyperpigmentation in Addison’s disease

Question 14

GH and ACTH have circadian rhythms, when are they active?

Answer 14

GH secretion is elevated shortly after sleep onset

ACTH is highest during early morning
- released by AP in response to stress → cortisol prod + release by adrenal cortex

Question 15

Posterior pituitary H are produced in the hypothalamus in which two nuclei?

Answer 15

1. Supraoptic nucleus

2. Paraventricular nucleus

Question 16

The supraoptic nucleus and paraventricular nucleus have neurons that extend into the posterior pituitary.
- name them and where they extend into

Answer 16

1. Magnocellular neurons → pars nervosa (infundibular process)
   - makes ADH and Oxytocin as large prohormones
2. Parvocellular neurons → median eminence (close to endings of hypothalamic neurons that produce Ant Pit regulating Hs)

Question 17

Some of the posterior pituitary Hormones can reach the anterior lobe where they can have some fxns (thanx to the parvocellular neurons)
- give 1 example

Answer 17

ADH secreted by Post Pit → act on corticotrophs to ↑ ACTH prod. → cortisol release → inhibit ADH fxn in kidney and release at hypothalamus

Question 18

Neurophysins

Answer 18

Carrier proteins:

Ships ADH and oxytocin to posterior pituitary from magnocellular neurons in hypothalamus
*prohormones are packaged as vesicles and are released with Ca2+ influx

Question 19

ADH is secreted in response to? Fxn?

Answer 19

1. ↑ plasma osmolarity
2. ↓ BP

• acts on cells of renal tubule and collecting ducts to alter water permeability and conserve water
• @ ↑ [ ] ADH acts as a powerful presser and ↑ BP

Question 20

Two kinds of ADH receptors

Answer 20

V1: coupled to Gq → PLC → mediates vasopressive action of ADH

V2: coupled to Gs → cAMP pathway regulates effects of ADH on GFR in kidney