Hypothalamic Adenohypophyseal Axis Flashcards
What produces GH
Somatotrophs
2nd msgr gonadotroph
PLC
2nd msgr thyrotroph
PLC
Corticotroph 2nd messenger
AC
somatotroph 2nd messenger
AC
lactotroph 2nd messenger
decrease AC, increase K, decrease Ca
what are the catecholamines
dopamine, epi, norepi
what hormones are cleaved from POMC mRNA?
ACTH and MSH; also beta endorphin and beta lipotropin
what is secreted from the arcuate nucleus
MSH, dopamine, GHRH, somatostatin
what is secreted from supraoptic nucleus
oxytocin, ADH (mostly)
what is secreted from preoptic nucleus
GnRH
what is secreted from periventricular nucleus
somatostatin
what is secreted from paraventricular nucleus
oxytocin (mostly), ADH, TRH, CRH
what do beta endorphins do
systemically reduce stress and maintain homeostasis locally amygdala (memory, emotion, pain perception) and hypothalamus (homeostasis)
what is substance P
neurotransmitter involved in pain responses
what are endorphins
released by the pituitary gland in order to block pain perception
what do endorphins bind to
bind to opiate receptors located on the presynaptic membrane and block the release of substance P
what causes release of melanin
melanocytes are stimulated by MSH (facilitated by UV light)
what is released by the anterior pituitary
ACTH/MSH, TSH, LH, FSH, prolactin
what cells release TSH
thyrotrophs
what cells release FSH and LH
gonadotrophs
what cells release GH
somatotrophs
what cells release prolactin
lactotrophs
what cells release POMC hormones
corticotrophs
cell type majority in anterior pituitary
somatotrophs – GH
metabolism of growth hormone
liver
metabolism of prolactin
kidney
primary function of GH
systemic increase in body weight, size, length, protein synthesis, mitosis
half life of GH
10min is 1-5ng/ml unbound
half life of prolactin
15-20min, 10ng/ml unbound
primary function of prolactin
milk synthesis, breast development, osmoregulation, poss carb metabolism
when is GH released
primarily at night, rhythmically
what stimulates GH?
GHRH
- hypoglycemia
- decrease in FFA
- increase in arginine
- fasting or decreased calories
- ghrelin
- REM sleep
- stress/exercise
- puberty
- sex hormones (testosterone)
what inhibits GH
GHIH
- hyperglycemia
- increase in FFA
- increase in GH
- increase in somatostatin that is from the anterior pituitary
how does GHRH stimulate GH release
binds to Gs, stimulates AC, increase cAMP, stimulate PKA, P proteins stimulate GH mRNA, GH released
how does GHIH inhibit GH release
GHIH binds to Gi which inhibits AC
what regulates growth hormone secretion?
- negative feedback from GHRH to hypothalamus
- negative feedback from somatomedins (insulin like GF) to anterior pituitary
- positive signal from somatomedins to hypothalamus to release somatostatin
- positive signal from GH to hypothalamus to release somatostatin
what hormone is secreted by the liver?
insulin like growth factor (IGF) is stimulated by GH and released by the liver
describe the IGF receptor
85% similar to insulin receptor, is a tyrosine kinase domain
what is the growth hormone signal transduction pathway
tyrosine kinase JAK STAT MAPK pathway
action of GH on liver
liver to produce somatomedins (IGF) to
- cartilage and bone (growth)
- muscle and other organs (protein synthesis and growth)
action of GH on adipose
lipolysis and release of FFA
does GH directly act on bone and muscle/organs?
indirectly through liver
action of GH on most other tissues
decreased glucose utilization
what occurs with hyposecretion of GH
before puberty: pituitary dwarfism
unrelated to GH: non pituitary dwarfism
what occurs with hypersecretion of GH
before puberty: gigantism
after: acromegaly
what occurs in achondroplasia?
fibroblast growth factor receptor problem – cannot contribute to production of collagen, short bone and cartilage
what occurs in laron dwarfism
GH receptor mutation
what is the blood response to insulin
decreased blood glucose, FFA, AA
blood response to glucagon
increased blood glucose and FFA, decreased AA (kinda)
blood response to GH
- increased blood glucose (decreased organ utilization)
- increased FFA (increased lipolysis and increased release of FFA from adipose)
- decreased AA (increased protein synthesis and growth)
which hormones use AC and cAMP?
- ACTH
- LH
- FSH
- TSH
- ADH (v2)
- hCG
- MSH
- CRH
- calcitonin
- PTH
- glucagon
- beta 1 and 2 receptors
- GHRH (both cAMP and IP3/DAG)
which hormones use IP3/PLC
- GnRH
- TRH
- GHRH (both cAMP and IP3/DAG)
- angiotensin II
- ADH (v1)
- oxytocin
- alpha 1 receptors
which hormones use steroid hormone mechanism?
- glucocorticoids
- estrogen
- progesterone
- testosterone
- aldosterone
- 1-25 dihydroxycholecalciferol
- thyroid hormones
what hormones use tyrosine kinase mechanism?
- insulin
2. IGF-1
what hormones use cGMP
- ANP
- endothelial derived relaxing factor
- NO
when is prolactin released?
all during the night
what stimulates prolactin
pregnancy, estrogen, nursing, TRH (pharmacological dose), dopamine antagonist
**no true hypothalamic stimulator of prolactin
what inhibits prolactin
dopamine (PIH), dopamine agonists, GHIH, GnRH associated peptide (GAP), prolactin
what does dopamine do with prolactin
lowers cAMP and Calcium
how is prolactin regulated
prolactin directly stimulates release of dopamine from hypothalamus which inhibits its release from AP.
TRH positively affects prolactin release.
trace the stimulus of suckling to lactation
- suckling starts. is sensed.
- sensory info sent to hypothalamus
- hypothalamus releases oxytocin to PP, prolactin to AP.
- oxytocin causes milk ejection
- prolactin causes milk production
how does prolactin cause milk production
binds to receptor that causes cytoplasmic tyrosine kinase chain. impacts mRNA synthesis that makes enzymes for lactose synthesis, enzymes for lipid synthesis, and casein.
describe hyposecretion of prolactin
hypolactogenesis
difficulty producing milk
what happens in hypersecretion of prolactin
- amenorrhea
- galactorrhea (milk flow not associated with childbirth/nursing)
- witch’s milk - milk excreted from infant
what could cause galactorrhea?
elevated TSH or TRH
