Normal Growth Flashcards
another name for somatotropin
growth hormone
two hypothalamic neurohormones that regulate growth hormone
GH-inhibiting hormone and GH-releasing hormone
after what age does GH become the main factor influencing growth
about 10 months
how does hypothyroidism stunt a childs growth
thyroid hormones have a permissive effect on GH
low thyroid levels –> low GH action
how does diabetes stunt a childs growth
insulin has a permissive effect on GH and so in diabetes where insulin is low GH is underactive
what is GH used for in adults
maintenance and tissue repair
what doe GH do to cell size and cell division
stimulation cell growth and cell division
the tropic action of GH stimulates what hormone
IGF-1, insulin-like growth
factor, from the liver
what is “insulin-like” about IGF-1
it has similar structure to pro-insulin and binds to very similar receptors
how does GH and IGF-1 exist in the blood
about half free and the other half bound to carrier proteins
effect of IGF-1 on GH
negative feedback on GH through acting on GHRH and GHIH accordingly, as well as on anterior pituitary
another name for IGF-1
somatomedin C
GH and IGF-1 actions on bone growth
growth hormone makes prechondrocytes in epiphyseal plates differentiate to chondrocytes. in the process they secret IGF-1, the IGF-1 then promotes the chondrocytes to further differentiate and produce cartilage
what effect of adolescence causes the epiphyseal plates to close
sex steroid hormones
effect of GH on gluconeogenesis
increases it
effect of GH on insulin
inhibition
how does GH aid lipolysis
by making adipocytes more sensitive to lipolytic stimuli
why is GH said to be diabetogenic
because it raises blood glucose through an anti-insulin effect
what actions make GH unlike cortisol and like insulin
increasing aa uptake and protein synthesis, essentially being anabolic
what anabolic action does growth hormone not do that insulin does
increase glucose uptake
what stage of life has the highest rates of GH secretion
teenage years
what time of day is most GH released
in first two hours of sleep ( deep delta sleep)
why is 24 hour monitoring necessary to get a true picture of GH levels
because it undergoes rapid spontaneous fluctuations so a single sample may be a very poor representation
true/false IGF-1 varies with GH levels
false - they remains relatively constant despite spikes suggesting that IGF-1 has some kind of buffering ability
oestrogen, testosterone, amino acid increase, stress, delta sleep and decreased energy supply to cells all have what effect on GHRH
stimulate GHRH secretion
free fatty acids, REM sleep and cortisol all have what effect on GH secretion
inhibitory. these stimuli increase GHIH
hormone periods through gorwth
thyroid a lot in early years
Androgens and oestrogens in later
GH prominent from infancy till end
main hormones of intrauterine growth
Insulin and IGF-II
what is cretinism
hypothyroidism from birth causing reduced permissive effects on GH. They have retarded growth and retain infantile facial features
nutrition in growth
need adequate vitamins, minerals, calories and protein to support growth
what is notable about infantile growth
episodic. huge growth spurts and then nothing.
place of sex hormones in puberty
permissive to GH and so stimulate growth but then terminate growth in bones at epiphyseal plates
what happens when GH is over secreted before epiphyseal plates fuse
they just grow and grow to be really big.
Pituitary giants
what happens when GH is over secreted after the epiphyseal plates fuse
grow in ways other than in long bone, so no height increase.
but hands a feet and other flat short bones grow
what is the most common cause of excessive GH secretion
an endcrine tumour of the pituitary gland
deficiency of GHRH causes
dwarfism, can be treated with supplement GHRH
What is Laron Dwarfism
target tissues are unresponsive to GH. They get increased GH the receptors will not respond and so IGF-1 won’t be released to inhibit GH through negative feedback loop
What happens in precocious puberty
there is stimulation of GnRH and so sex hormones are secreted early and cause long bones epiphyseal plates to fuse, stunting their growth
what differs, physically, between hypothyroid children and GH deficient children
hypothyroid children are short, fat and retain infantile faces, whereas GH deficient children have normal proportions but are just small
effect on GH secretion when plasma glucose falls following insulin
GH secretion stimulated via GHRH.
GH then increases gluconeogenesis and makes insulin less effective
effect on GH secretion when plasma amino acids rise after digestion
increased aa –> GHRH secretion –> GH secretion –> increased amino acid uptake and protein synthesis
