HRR: growth hormone Flashcards
Where is growth hormone made?
In somatotrophs in the anterior pituitary
What is the most important hormone required for growth?
Pituitary growth hormone
What are tropic hormones?
Pituitary hormones
What does GHRH do?
Regulate GH release via pulsatile release
Where is GHRH made?
Neurons in the arcuate nucleus
What does GHRH promote?
Somatotroph differentiation, GH synthesis/secretion, growth
How does GHRH promote GH release?
Binds its receptor on the somatotroph and increases GH mRNA transcription and thus synthesis of GH
What does somatostatin do?
It inhibits GH secretion by inhibiting GHRH arcuate neurons in the hypothalamus and blunts GH responses to GHRH at the pituitary
Where is somatostatin made?
The paraventricular nucleus
How does IGF-1 impact GH secretion?
It inhibits GHRH neurons and stimulates somatostatin neurons in the hypothalamus and inhibits GHRH stimulated GH release at the pituitary
How can GH impact its own release?
In high levels, it feeds back to the hypothalamus and binds GH receptors on somatostatin neurons to limit GH release
Describe ghrelin in relation to GH.
It is a growth hormone secretagogue, meaning its effects are similar to GHRH; they increase GH release
What receptor does ghrelin use?
GHSR
Where is most ghrelin made?
In the stomach! Some is made in the pituitary
Describe the effects of ghrelin.
It is released during fasting and promotes food intake
How do GH and ghrelin impact each other?
Their effects are additive!
When are the greatest increases in GH?
At night after the onset of sleep
What happens to pulsatility of GH as we age?
Frequency and amplitude of the pulsatility decrease; it peaks around puberty and declines after that
When is a single GH blood sample useful in diagnosis?
Literally never. Daytime levels are normally extremely low
What causes IGF-1 production?
GH engages its receptors, often at the liver, leading to signaling pathways and causing synthesis of IGF-1
What is the major site of IGF synthesis?
The liver
How does IGF-1 impact glucose uptake?
It increases the uptake of glucose! It can bind and stimulate insulin receptors to stimulate glucose uptake
Compare actions of GH and IGF-1.
They’re really similar. Sometimes it’s hard to biologically tell which hormone did what
How do GH and IGF impact bones?
Increases linear bone growth! Without it the growth plates are narrow, and cartilage production is low.
Cells in the growth plates of bones contain what hormone receptors?
Androgen, estrogen, testosterone, GH, IGF-1
How does estrogen impact bone?
It is protective and increases stability
How does GH impact blood glucose?
Increases it; it increases gluconeogenesis in the liver and decreases glucose uptake in fat/muscle
What does exercise do to GH?
Increases it
What may be associated with GH deficiency?
Abnormal metabolism (lower basal metabolic rate), abnormal body composition (increased body fat), suboptimal physical performance (it is performance enhancing!!)
What causes Gigantism?
Excess GH prior to puberty
What causes dwarfism?
GH deficiency prior to puberty
What might a child with GH deficiency look like?
Smaller stature, smaller limbs, smaller trunk, immature face, “baby fat”
What causes acromegaly?
Excess GH after puberty, usually due to a pituitary tumor
What might someone with acromegaly look like?
Mandibular prominence, nasal soft tissue enlargement, thickening of hands and feet, prominent forehead. It’ll alter the bone structure, which shouldn’t happen after puberty
What does hypoglycemia do to GH?
Increases it
What do amino acids do to GH?
Increases it
What does puberty do to GH?
Increases it
What does ghrelin do to GH?
Increases it
What does somatostatin do to GH?
Decreases it
What does somatomedin do to GH?
Decreases it
