control of growth

Question 1

what cells produce growth hormone

Answer 1

somatotroph cells

Question 2

what tissue does growth hormone target

Answer 2

all tissues

Question 3

what % of the pituitary gland comprises of somatorophs

Answer 3

40-50%

Question 4

growth hormone synthesis pathway (from hypothal)

Answer 4

neurons in arcuate nucleus of hypothal secrete GHRH -> hyophyseal portal blood -> GHRH binds to G-protein couples receptors on somatotrophs -> activates Gα -> adenyl cyclase activation -> increase cAMP leading to gene transcription and synthesis of GH

Question 5

how is GH released from cells

Answer 5

PKA allows Ca2+ Chs to open -> C2+ enters cell -> vesicles containing GH are exocytosed

Question 6

what hormone can inhibit GH secretion and where is it produced

Answer 6

somatostatin can inhibit GH secretion, it is produced in the periventricular region of the hypothal

Question 7

what is the role of IGF-1 in the GH cycle

Answer 7

negative feedback -> GH produced IGF-1 which in turn inhibits GH at the hypothal. and pit. levels

Question 8

how does ghrelin affect GH

Answer 8

increases hypothalamic GHRH production which thus increases GH production

Question 9

role of oestrogen in GH axis

Answer 9

1. inhibit the release of IGF-1 fro the liver (GH release is not inhibited)
2. potentiate pituitary GH response to pulses of GHRH
3. mute inhibition from somatostatin
4. potentiates ghrelin’s action

Question 10

how do somatotroph cells change throughout ife

Answer 10

the characteristics and number remain the same but their secretion pattern changes

Question 11

what are the characteristics of GH secretion

Answer 11

1. rhythmic characteristics -> secretion occurs in a pulsatile manor every 2hrs
2. circaidian rhythm affects GH secretion -> maximum release at night

Question 12

when do maximum GH levels occur in the course of a day

Answer 12

at night -> within minutes of slow wave sleep

Question 13

what physiological factors also affect GH secretion

Answer 13

gender; age; pubertal status

Question 14

3 physiological causes for GH secretion

Answer 14

1. in response to hyogycaemia being sensed by the hypothalamus
2. in response to exercide, stress, trauma etc.
3. secretion during puberty

Question 15

4 direct effects of GH

Answer 15

1. stimulation of cellular metabolism leading to tissue growth
2. releases fatty acids from adipose tissue
3. promotes gluconeogeneis + glycogenolysis
4. insulin resistance -> decreases glucose uptake and ultilisation by target tissues -> increase [blood glucose] ->diabetogenic

Question 16

what organs secrete somatomadins (3) and what does this do

Answer 16

liver, muscle and bone -> leads to somatostatin secretion -> inhibits GH

Question 17

3 indirect effects of growth hormone

Answer 17

1. steady release of somatomadin -> release of IGF-1
2. binds to receptors promoting cellular metabolism, prevents cell death, increases cell division
3. amino acid uptake in muscle cells

Question 18

what is IGF-1

Answer 18

insulin like growth factor 1 -> a polypeptide that has a major role in metabolism and proliferation