hormonal control of growth Flashcards
effects of GH
increased protein synthesis
increased amino acid transport
increased lipolysis
reduced liver glucose uptake and increased gluconeogenesis
increased IGF production (insulin like growth factor)
growth hormone release is
circadian and pulsatile
GH release is triggered by
Growth hormone releasing hormone
GH release is stopped by
somatostatin
things stimulating growth hormone
starvation, exercise, sleep
the starvation paradox
Gh helps survive prolonged starvation by switching metabolism away from proteins as a fuel source
protein sparing
makes you burn fats in preference to protein
indirect effects of GH are mediated by
insulin-like growth factor
liver provides most of circulating IGF-1
IGFs regulate
proliferation, differentiation and metabolism
resembles insulin structure and function
IGFs stimulate amino acid uptake and activate protein and DNNA synthesis
strongly mitogenic and hypertrophic
2 forms of IGF
IGF-1 = adult form IGF-2 = foetal form
GH will activate
IGF
local IGF
is produced in heart and skeletal muscle and bone
IGF-1 regulation
growth rates reflect IGF levels
IGF responds to feasting
insulin potentiates GH effects
GH cannot increase IGF levels in the absence of insulin
normal growth requires normal levels of both GH and insulin to increase IGF
to increase IGF1 normal levels of _ are required
both insulin and GH
insulin potentiates GH effects
negative feedback of GH IGF axis
GH gives negative feedback to hypothalamus and IGF gives negative feedback to anterior pituitary and hypothalamus
over secretion of Gh usually due to
benign tumour (adenoma)
over secretion of GH before puberty
this can lead to excessive growth that continues throughout childhood and puberty, leading to an extremely tall stature or gigantism
over secretion of GH after puberty
this can lead to thickening of the bones of the hands, feet and jaw, causing disease known as acromegaly
effects of acromegaly
cartilage enlarges, increasing the size of the nose and ears
increase in bone and cartilage often impinges on certain nerves
visual-field losses due to pressure on the optic nerves
ball’s palsy (facial paralysis on one side) due to pressure on the facial nerve
carpal tunnel syndrome: pressure on median nerve in first by excessive bone/tendon growth
spreading teeth, bite difficulties
joint and bone aches and pains
soft tissue enlarge, including the heard leading to cardiac hypertrophy
hypertension is also common
under secretion of GH
under secretion of Gh before puberty causes dwarfism
after puberty, patients show few clinical symptoms
factors that may reduce pituitary GH output
tumour e.g. of the hypothalamus which over secrete somatostatin
infections can affect hypothalamic GHRH of somatostatin secretion and alter GH release
GH secretion is very susceptible to irradiation e.g. after cranial radiotherapy
GH receptor/signalling defects
dwarfism, pygmyism
laron-type dwarfism
genetic polymorphism reducing GH receptor expression
Baka pygmy
normal GH levels but reduced IGF production
steroid hormones
androgens play a synergistic rose i.e. linear growth, increase muscle strength and mass, stimulating protein synthesis in many organs
testosterone and oestrogen also enhance the growth hormone release and function
thyroid hormone
adequate levels of TH are required for normal growth
thyroid hormones act primary through stimulation of booth GH synthesis and secretion
TH may also increase the responsiveness of target cell to GH
low thyroid hormones levels lead to
declining GH levels
stunted growth observed in thyroid deficient individuals is primary due to a deficiency in GH
GH replacement
recombinant hGH developed to treat GH deficiencies in children, as well as cachexia and muscle wasting disorders
hormones replacement therapy
aging - reduced lean muscle and bone mass, increase n body fat - similar to changes associated with endocrine deificency
sport use of hormonal growth promoters
hGH has long been a banned substance in competition
GHRH peptides - act on the pituitary gland to stimulate the release of Gh
putative benefits - lean body mass, increase muscle mass and strength, injury resistance
use of hormonal growth promoters
increase skeletal mass and lean body mass, decrease in body fat
side effects - carpel tunnel syndrome, hypertension, joint and bone aches, cancer
incidence of malignant tumours higher in patients with acromegaly
IGF signalling implicated in aging
