Normal growth & clinical aspects

Question 1

does insulin stimulate or inhibit growth?

Answer 1

stimulates growth

Question 2

what is the functions of growth hormone and is this direct and indirect effects?

Answer 2

growth and development (indirect)
regulates metabolism (direct)

Question 3

what is required to allow GH to stimulate growth?

Answer 3

thyroid hormones & insulin

Question 4

in adulthood when we stop growing, what is GH required for?

Answer 4

GH is required for maintenance and repair of tissues

Question 5

what is responsible for the indirect action of GH on growth?

Answer 5

somatomedian C

IGF-1

Question 6

where is IGF-1 secreted from and what promotes its release?

Answer 6

GH stimulates IGF-1 release from the liver

Question 7

how does IGF-1 provide a negative feedback loop to GH?

Answer 7

IGF-1 inhibits the release of GHRH and stimulates GHIH

can also have an effect on the release of GH from the anterior pituitary

Question 8

during puberty when there is massive spikes in GH production, what provides a buffering mechanism so that adolescences don’t grow in dramatic bursts?

Answer 8

50% of GH is bound to carrier proteins which helps to smooth out the erratic pattern of secretion
also provides a reservoir of GH in the blood when required

Question 9

the closure of the epiphyseal plates after puberty is due to what hormone?

Answer 9

sex hormones

Question 10

what is responsible for the production of cartilage in bone growth?

Answer 10

GH stimulates the differentiation of chondrocyte precursors to form chondrocytes.
these cells then begin to secret IGF-1 which they then respond to
IGF-1 lays down the cartilage which is the foundation for bone growth

Question 11

how does GH have a direct effect on metabolism?

Answer 11

GH increases gluconeogenesis in the liver to increase glucose
it also reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue
this causes hyperglycaemia making glucose readily available to cells needing it for growth

Question 12

in patients who have an increase in GH release, how might they present with diabetogenic signs?

Answer 12

GH increases blood glucose in order to mobilise energy stores to make it readily available for cells who require glucose for growth

Question 13

what effect does GH have on muscle, liver and adipose tissue?

Answer 13

GH decreases insulin’s ability to stimulate glucose uptake by muscle, liver and adipose tissue
however GH increases the amino acid uptake and protein synthesis

Question 14

because GH inhibits the actions of insulin, how does it increase the uptake of glucose by other cells who require it for growth?

Answer 14

GH inhibits insulin to increase blood glucose to make it readily available for tissues who require it for growth
but liver, muscle and adipose tissue are the only tissues that are insulin sensitive
therefore other cells are able to uptake the glucose without insulin

Question 15

when is release of GHRH at it highest and why?

Answer 15

during deep delta sleep because this is when we have our lowest energy requirements

Question 16

what provides the buffering qualities to GH release during sleep and how?

Answer 16

IGF-1

levels remain constant during sleep despite the dramatic fluctuations of GH

Question 17

what are stimuli that increase GHIH?

Answer 17

glucose
FFA
REM sleep
cortisol

Question 18

what stimuli increase GHRH?

Answer 18

decrease in energy supply to cells
increased AA in plasma 
stressful stimuli e.g. infection 
delta sleep
oestrogen and testosterone

Question 19

why does an increase of AA stimulate GHRH but an increase in glucose stimulates GHIH?

Answer 19

GH promotes AA uptake and protein uptake by muscle and liver

whereas GH promotes an increase in blood glucose by reducing the ability of insulin to stimulate glucose uptake

Question 20

for growth and development, IGF-1 promotes the uptake of glucose into what type of tissue?

Answer 20

muscle

Question 21

what is cretinism?

Answer 21

a condition where a child is hypothyroid from birth

Question 22

why does hypothyroidism from both cause stunted growth?

Answer 22

thyroid hormone is permissive to the actions of GH

therefore with no TH the GH won’t be stimulated despite normal levels

Question 23

what is the cause of gigantism and acromegaly ?

Answer 23

gigantism is caused by an over secretion of GH before the epiphyseal plate closes
Acromegaly is over production after it closes

Question 24

how would you treat gigantism or acromegaly?

Answer 24

resection of pituitary tumour

somatostatin analogues

Question 25

what may be some of the causes of dwarfism?

Answer 25

deficiency in GHRH
abnormal GH secretory cells so less GH released in response to GHRH
end organ unresponsive to GH ( = high GH in plasma)
genetic mutations
precocious puberty (excess GnRH so long bones fuse early due to early influence of sex hormones)
hypothyroid (permissive effects of TH on GH)