Hypothalamic Control of the Pituitary Gland Flashcards Preview

DEMS: Unit III > Hypothalamic Control of the Pituitary Gland > Flashcards

Flashcards in Hypothalamic Control of the Pituitary Gland Deck (16):
1

Mechanism of hypothalamic-pituitary communication

  • The hypothalamo-hypophysial portal system connects the hypothalamus to the anterior pituitary
  • Hormones are carried in this tiny portal system.
    • local release restricts the amount of blood exposed to the released hormone
    • thus the hypothalamic hormones don’t get diluted by the time they reach the anterior pituitary.  
  • This allows for very tiny amounts to be released to reach the anterior pituitary in high concentrations.

2

Hypothalamic hormones that regulate anterior pituitary fxn

  • Thyroid Releasing Hormone (TRH)
  • Corticotropin Releasing Hormone (CRH)
  • Growth Hormone Releasing Hormone (GHRH)
  • Somatostatin (SST)
  • Prolactin Inhibiting Hormone (PIH)*
    • PIH = Dopamine (DA)
  • Gonadotroph Releasing Hormone (GnRH)

3

Thyroid releasing hormone (TRH): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • Receptor/cell type
    • Gq; Thyrotrophs
  • AP action
    • ↑ TSH
    • (↑ PRL)
  • Downstream
    • ↑ Thyroid Hormone from thyroid

4

Corticotropin releasing hormone (CRH): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • Receptor/cell type
    • Gs; Corticotrophs
  • AP action
    • ACTH
  • Downstream
    • ↑ Cortisol from adrenal cortex

5

Growth Hormone releasing hormone (GHRH): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • receptor/cell type
    • Gs; Somatotrophs
  • AP action
    • ↑ GH
  • Downstream
    • Acts alone

6

Somatostatin (SST): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • receptor/cell type
    • Gi; Somatotrophs.
  • AP action
    • ↓ GH
  • Downstream
    • Acts alone

7

Prolactin Inhibiting Hormone (PIH): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • receptor/cell type
    • Gi; Lactotrophs
  • AP action
    • ↓ PRL
  • Downstream
    • Binds cytokine receptor, causes dimerization → activation of JAK/STAT →  gene expression.
    • ~300 effects
    • Mammary gland →  mammogenesis, lactogenesis, and galactoporesis.
  • Under normal circumstances, prolactin is inhibited.

8

Gonadotropin Releasing Hormone (GnRH): Ant. Pituitary Receptor/Cell type + AP action + downstream action

  • receptor/cell type
    • Gq; Gonadotrophs.
  • AP action
    • ↑ LH + ↑ FSH
  • Downstream
    • ↑ Estrogen and Progesterone

9

One sentence summary of mechanism hormone communication from hypothalamus ==> anterior pituitary

Stimulus-dependent (AP arrival) secretion of hypothalamic hormones is analagous to neurotransmitter release (just switch hormone for NT), and is thus calcium-dependent secretory vesicle release.

 

10

Principles of hormone release from hypothalamic neurons

  • Calcium dependent exocytosis (same mechanism as neurotransmitter release)
  • Pulsatile release (plasma shows spikes)
  • Endogenous pacemakers regulate pulsatile secretion
  • Pulsatile secretion of hypothalamic hormone signals pituitary secretion, e.g. pulse of GnRH precedes LH pulse
  • Circadian rhythms of secretion (GH high after bedtime, ACTH high in early a.m.)

11

Main receptors/signal transduction mechanisms for hypothalamic hormones

  • All receptors for hypothalamus hormone are G coupled → Gs, Gi, Gq.
  • There is a lot of interaction with various receptor types and a given hormone.
  • Multiple pathways can be activated by a single hormone

12

Hypothalamus origins/connections to brain

  • Hypothalamus is derived from the third ventricle
  • receives inputs from the thalamus, limbic system (olfactory bulb, hippocampus, habenula (stalk of pineal gland), & amygdala), retina, reticular activating substance & neocortex.
  • Basically, this allows things like emotions, light, pain, etc. to affect hormone release.

13

Hypothalamic nerve terminal location & mechanism of neurohormone release

  • Nerve terminals from hypothalamic neurons terminate @ median eminence
    • secrete hormones into a capillary plexus formed by blood coming from the superior hypophyseal arteries.
  • These neurohormones ==> portal venous system into the anterior pituitary into a second capillary plexus.
  • This is all outside of the blood brain barrier.

 

14

Posterior pituitary hormones synthesis location + cell types

  • Posterior pituitary hormones (ADH & oxytocin) are synthesized in the supraoptic nucleus and paraventricular nucleus which have two cell types:
  • Magnocellular neurons terminate in pars nervosa; make both ADH & oxytocin
  • Parvocellular neurons terminate at median eminence, thus hormones can be taken up into the portal system and affect the anterior pituitary (e.g., CRH can ↑ ACTH).

15

Characteristics of type 1 feedback loop control of hypothalamic hormone release

  • Type 1 feedback loop → Hormone is regulated variable
  • Negative feedback loop: most common, regulated variable is plasma conc. of hormone. Often times excess hormone inhibits further production of itself by acting upstream. (e.g. T4 inhibits Thyrotrophs)
  • Positive feedback loop: rare, ends with expulsion of something (like a baby, w/oxytocin)

16

Characteristics of type 2 feedback loop control of hypothalamic hormone release

  • Type 2 feedback loop → Plasma concentration of a metabolite or mineral,
  • e.g., blood glucose - when it drops, glucagon is secreted, when it increases, insulin is secreted