Growth Hormone Flashcards
what is the effect of growth hormone on urinary nitrogen and serum urea?
GH is anabolic (building) hormone - therefore, increases nitrogen RETENTION (decreased urinary nitrogen) + LOWERS serum urea
where is growth hormone receptor most prominent?
liver, cartilage, muscle, fat, kidney
how can growth hormone affect body fluid status?
GH promotes Na+ reabsorption in the kidney —> increased total body fluid
describe the effects of growth hormone on fat and glycogen metabolism, respectively
GH promotes lipolysis, mainly in visceral fat, to increase availability of glycerol and FFA for muscle work
GH shunts metabolism from glycogenolysis to FFA metabolism to acetyl CoA for ATP - thus supports conservation of glycogen stores and decreases cellular uptake of glucose
what is the only proglycemic anabolic hormone?
growth hormone - preserves plasma glucose by
1) blocking glucose uptake by skeletal muscle (promotes insulin resistance)
2) shunting metabolism from glucose to FFA oxidation
acts as counter-modulator to the catabolic actions of glucocorticoids in skeletal muscle (prevents utilization of muscle amino acids for ATP production)
what is the purpose of IGF and GH binding proteins (IGFBPs and GHBPs, respectively)?
circulating isoforms of truncated IGF and GH receptors produced by liver
carrier proteins, extend the half-life of circulating GH and IGF-1, aid in delivery to target tissues, reduce renal clearance
which nucleus of the hypothalamus secretes growth hormone releasing hormone (GHRH)?
ventromedial nucleus
what is the effect of dopamine on growth hormone?
dopamine stimulates growth hormone secretion from somatotrophs of anterior pituitary
which amino acids (2) stimulate growth hormone release?
high protein meals and amino acids arginine and lysine stimulate GH release
what is the effect of alpha2 vs beta2 adrenergic activation on growth hormone secretion?
alpha2 adrenergic receptors stimulates GH
beta2 adrenergic receptors are coupled to release of somatostatin, thus down-regulate GH secretion
approximately 85% of daily growth hormone production is attributed to…
… its circadian rhythm - there is an increase in GH secretion during the first hours of sleep (REM), probably in response to hypoglycemic state
that is why it’s so important for growing kids to get their sleep!!
how is suppression testing used to measured serum growth hormone?
remember GH is tricky to measure because it is secreted in pulsatile waves
in suppression testing, patient is given oral glucose and blood GH is drawn at timed intervals
failure to lower GH below 2ng/ml indicates loss of negative feedback and is considered a positive test for excessive GH secretion
what is the reference standard for making a diagnosis of adult growth hormone deficiency?
remember GH is tricky to measure because it is secreted in pulsatile waves
to detect deficiency, you need to try to induce GH secretion - this can be done with insulin, which causes hypoglycemia and subsequent GH secretion
insulin induced hypoglycemia is reference standard
