Pituitary Gland Flashcards
Anterior pituitary lobe
Adenohypophysis
Posterior pituitary lobe
Neurohypophysis
3 Pathways that regulate pituitary gland
- Hypothalamic inputs
- Feedback effects of circulating hormones
- Paracrine/autocrine secretions of circulating hormones
CRH axis
CRH –> ACTH –> adrenal
GnRH axis
GnRH –> FSH/LH –> gonads
TRH axis
TRH –> TSH –> thyroid
GHRH axis
GHRH –> GH –> liver +
Dopamine axis
Dopamine –> PRL –> breast
How are hormones transported from Hypothalamus to anterior pituitary?
median eminence –> Portal blood of portal stalk
Hypothalamic releasing hormones
Stim release of stored pituitary hormones
Stim synth of pituitary hormones
Tiny
Short plasma half lives
Corticotropin Releasing Hormone (CRH)
Stim synth & release of ACTH (corticotropin) from corticotroph cells (and POMC)
Half life 6-10 min and 40-50 min (biphasic)
Effects on ACTH potentiated by ADH & Angiotensin II
Gonadotropin Releasing Hormone (GnRH)
Stim synth & release of LH & FSH from gonadotroph cells
Half life 2-4 min
Dopamine
Inhibitory fx to dec prolactin synth & release from lactotroph cells
Thyrotropin Releasing Hormone (TRH)
Stim synth & release of TSH from thyrotroph cells
Half life 6 min
Also stim prolactin release at high []
Somatostatin (STT)
Inhib of GH synth & release from somatotroph cells
Also inhib TSH
Half life 2-3 min
Growth Hormone Releasing Hormone (GHRH)
Stim secretion & release of growth hormone from somatotroph cells
Half life 3-7 min
Ant Pituitary hormone general facts
Larger molecules
Made in troph cells
Systemic release
Which of the main ant pituitary hormones does not stim peripheral hormone secretion?
PRL
Dopamine
(-) by Dopamine
(+) by estrogen & TRH
Hyperprolactinemia
Inhib gonadotropin secretion
Causes galatorrheaC
Can be caused by psych meds, nipple stim, prolactinomas, idiopathic
GH regulation
GHRH (+)
SST (-)
Ghrelin (+)
B-ad antag (+)
A-ad ag (+)
Insulin-like Growth Factor-1 (IGF-1)
Synth/secreted by liver (& others) in response to GH
Mediates many GH effects
Binds to IGF-1R & insulin-R to stim mitogenic & growth effects
Where does IGF-1 exert endocrine effects
Bone
Cartilage
Muscle
SST secretion stim by:
GH (+)
IGF-1 (+)
How does SST (-) on GH?
SST-R are Gi coupled on GPCR –> dec cAMP
Ghrelin
Stim GH secretion directly & in synergy w GHRH
Fasting (+)
What feedback loops monitor ghrelin?
Hypothalamus
Stomach
Liver
GH secretion pattern
Pulsatile
GH levels difficult to interpret
2/3 of production during slow wave sleep (diurnal rhythm)
GH effects on plasma glucose
- Dec glucose uptake
- Inc hep gluconeogenesis
- Inc hep glycogenolysis
- Dec insulin sensitivity
GH effects on plasma FA
- Inc adipose lipolysis
- Inc muscle B-ox of FA in muscle
How does GH affect muscle and organs?
Promotes growth
- Inc prot synth
- Dec prot breakdown
Mitogenic effects of GH & IGF-1 on SKM
GH (via IGF-!):
Inc prot synth from bone cells
Inc bone length (children)
Inc bone width
Miscellaneous mitogenic effects of GH & IGF-1
Growth of visceral organs
Skin thickening
Miscellaneous mitogenic effects of GH
Sweat gland hyperplasia
Hair growth
Plasma calcitriol
Miscellaneous mitogenic effects of IGF-1
Hemoglobin/hematocrit action on bone marrow
Inc GFR
Symtoms of GH Deficiency
Ateleotic dwarf Dec muscle mass Thin hair Thin skin Dec counter regulatory to hypo-g
Symptoms of GH excess
Gigantism Joint problems Enlarged jaw/brow/handsds/feet Hepatomegaly Splenomegaly
