Endocrine Control of Growth

Question 1

What hormones are most important for fetal growth and where are they produced?

Answer 1

IGF1 and IGF2, produced in the placenta and by the fetus

Question 2

Describe how IGF they differ from insulin.

Answer 2

IGF is predominantly a GH where insulin is predominantly metabolic

Question 3

What are the 3 main receptors of IGF?

Answer 3

INSR, IGF1R and IGF2R

Question 4

What hormones bind to IGF1R to stimulate growth?

Answer 4

IGF1 and IGF2 both bind to IGF1R

Question 5

Which hormone is most important in gestation and which most important at birth (IGF1/IGF2)?

Answer 5

IGF2 is primary GF in fetal life, IGF1 most important at birth

Question 6

Compare half life of unbound IGF in blood to IGF bound to protein.

Answer 6

Unbound IGF in blood has half life on 10mns, if bound to protein half life of 16hours

Question 7

What is the most abundant IGFBP in adults and where is it predominantly made?

Answer 7

IGFBP3 is most abundant in adult and is made predominantly by the liver

Question 8

Compare growth hormone levels at birth to later in childhood.

Answer 8

GH levels at birth can be 30 fold x higher than later childhood

Question 9

When does pulsatile secretion start to form and list its 2 main characteristics.

Answer 9

pulsatile secretion starts to form at birth, once regular pulses reached, frequency will always stay the same but the amplitude may change

Question 10

List some stimulatory and inhibitory factors for GH.

Answer 10

stimulatory: starvation/fasting, hormones of puberty, exercise, stress
inhib: obesity

Question 11

Describe what happens to amplitude of GH pulse during pubertal growth spurt.

Answer 11

Amplitude will have 2-3 fold increase

Question 12

What happens to females in puberty when estrogen reaches high enough level?

Answer 12

high estrogen level causes skeletal maturation and ossification of growth plates = final height

Question 13

What is estrogens effect on GHR signalling in liver and what other hormone does this effect?

Answer 13

estrogen suppresses GHR signalling in liver causing no increase in IGF and therefore no extra pathway of growth

Question 14

Describe testosterones relationship to GHR signalling in the liver and its effect on other hormones

Answer 14

testosterone increases GHR signalling in the liver increasing IGF levels

Question 15

what happens to testosterone to turn it into estrogen?

Answer 15

testosterone is aromatised into estrogen

Question 16

Why do males have more free GH during puberty?

Answer 16

GHBP levels are proportionate to adiposity in the body, since women have higher adiposity more of there GHs and bound to proteins

Question 17

What hormones stimulates GH when hungry?

Answer 17

ghrelin

Question 18

Discuss GH relationship with obesity

Answer 18

GH stimulates lipolysis which helps reduce weight and stop further GH production, high level of fatty acids decrease GH however leading to further weight gain

Question 19

explain relationship between GHR and GHBP

Answer 19

GHBP is soluble form of GHR