Hormoner: endokrin kontrol af vækst

Question 1

Knoglevækst

Answer 1

Højdevækst er afhængig af væksten af de lange rørknogler og ryghvirvlerne

Epifyse-vækstskive
Diafyse/shaft

Question 2

Væksthormon GH og højdevækst

Answer 2

Effekten af GH på højdevækst kræver at GH er unormal i de først leveår

Forøget cirkulerende GH efter lukning af vækstskiven kan resulterer i akromegali
- resulterer i abnormal vækst af fingre, fødder, tunge, læber, kæbe, pande og næse.
- Akromegali skyldes oftest en benign hypofysetumor

Hypofyse-betinget dværgvækst og gigantisme

Question 3

Skyldes GH’s indvirkning på højdevækst udelukkende en direkte effekt af GH på vækstskiven?

Answer 3

Experimental set-up:
- Epiphyseal cartilae growth (where longitudinal bone growth occurs) in vitro

Observations.
1) Serum from normal animals promoted growth
2) Serum from GH-deficient animals did not promote growth
3) Serum from GH-deficient animals supplemented with GH did not promote growth
4) Serum from GH-deficient animals treated in vivo with GH promoted growth

Interpretation:
- GH promotes the secretion of another circulating factor with growth-promoting properties

Question 4

Den hormonelle kaskade

Answer 4

1) Stimulus: exercise, stress, fasting, low plasma glucose, sleep
2) Hypothalamus: increased GHRH secretion and lowered SST secretion
3) Increased plasma GHRH and decreased plasma SST
4) Anterior pituitary: increased GH secretion
5) Increased plasma GH
6) Liver and other cells: increased IGH-1 secretion
7) Increased plasma IGF-1

Question 5

Feedback regulering

Answer 5

IGF-1 påvirker GHRH og GH negativt og SST positivt.

GHRH påvirker GH positivt

SST påvirker GH negativt

GH påvirker IGF-1 positivt og SST positivt

Bemærk:
I forhold til den generelle mekanisme for
feedback-regulering (slide 36), er
reguleringen her mere kompleks, da der
her både er et positivt og et negativt
virkende hypothalamisk hormon

Question 6

Effekter af GH

Answer 6

1) Promotes growth: Induces precursor cells in bone and other tissues to differentiate and secrete insulin-like growth factor 1 (IGF-1), which stimulates cell division. Also stimulates liver to secrete IGF-1

2) Stimulates protein synthesis, predominantly in muscle

3) Anti-insulin effects(particularly at high concentrations):
- Renders adipocytes more responsive to stimuli that induce breakdown of triglycerides, releasing fatty acids into the blood
- Stimulates gluconeogenesis
- Reduces the ability of insulin to stimulate glucose uptake by adipose and muscle cells, resulting in higher blood glukose concentrations

Question 7

Growth hormone

Answer 7

Major stimulus of postnatal growth: induces precursor cells to differentiate and secrete insulin-like growth factor 1 (IGF-1), which stimulates cell division.
Stimulates liver to secrete IGF-1
Stimulates protein synthesis

Question 8

Insulin

Answer 8

Stimulates fetal growth
Stimulates postnatal growth by stimulating secretion of IGF-1
Stimulates protein synthesis

Question 9

Thyroid hormone

Answer 9

Permissive for growth hormone’s secretion and actions
Permissive for development of the central nervous system

Question 10

Testosterone

Answer 10

Stimulates growth at puberty, in large part by stimulating the secretion of growth hormone.
Causes eventual epiphyseal closure
Stimulates protein synthesis in male

Question 11

Estrogen

Answer 11

Stimulating the secretion of growth hormone.
Causes eventual epiphyseal closure

Question 12

Cortisol

Answer 12

Inhibits growth
Stimulates protein catabolism

Question 13

Vigtigt at huske

Answer 13

1. Princippet ved knoglevækst
2. Væksthormons involvering i højdevækst
3. Den hormonelle GH-kaskade, der regulerer vækst,
   herunder betydningen af IGF-1 og feedback-regulering
4. Eksempler på andre hormoner med indvirkning på vækst