Endocrine 1: Growth hormone

Question 1

cells secreting HGH

Answer 1

Somatotrophic acidophilic cells
(somatotrophs)

Question 2

HGH is made up of ____ amino acids

Answer 2

191

Question 3

normal levels of HGH in adults

Answer 3

2-4 ng/ml

Question 4

Normal levels of HGH in children

Answer 4

5-8 ng/ml

nearly twice that of adults

Question 5

Describe mechanism of action of HGH on cells

Answer 5

1. binds to 2 GH receptors forming homodimer complex
2. Homodimer activates JAK2, causing autophosphorylation of JAK2, which causes:
   * activation of Protein Kinase C (PKC) & Phospholipase C (PLC)
   * stimulate phosphorylation of insulin receptor substrate (IRS)
   * phosohorylation (activation) of STAT proteins for protein synthesis

Question 6

STAT proteins stands for

Answer 6

Singal Transducer & Activator of Transcription

Question 7

Effect of growth hormone on Protein metabolism

Answer 7

(anabolic):
* Enhances AA uptake by the cells
* increases Trascription of mRNA
* Enhances RNA translation by ribosomes
* protein sparing effect (to not use AA for energy source)

Question 8

Effect of growth hormone on Carbohydrate metabolism

Answer 8

(Hyperglycemic)
1. Decreases glucose uptake by skeletal muscles & fat cells:
* decreases affinity of insulin receptor to insulin
* inhibits hexokinase, increase intracellular glucose, no more glucose diffusion into cells
* decrease glycolysis & glucose oxidation

2. Increase glucose production by liver:
   * Inhibits glucokinase enzyme, increasing intracellular glucose inside Liver, therefore decreasing uptake & increasing glucose release by the liver
   * glycogenesis of excess

Question 9

if GH secretion increases by ____ %, it’ll cause DM

Answer 9

100% (double)

Question 10

Effect of GH on Lipid metabolism

Answer 10

(increase blood FFA)
* Increase lipolysis to provide muscles with FFA as source of energy (compensatory for decreasing glucose uptake)
* increase uptake of FFA by liver (may cause fatty liver)
* Increase Ketone bodies & Acetyl CoA (increases Acetoacetic acid= Acidosis)

Question 11

effect of GH on soft tissue

Answer 11

• stimulates growth of all soft tissue of the body
• stimulates erythropoeisis
• produces positive Nitrogen balance

Question 12

GH stimulates cartiaginous growth indirectly by Intermediate substance called ____

Answer 12

Somatomedin C /IGF-1

Question 13

describe how somatomedin C increases growth of skeletal frame

Answer 13

In Length:
* IGF-1 deposits new cartilages at the epiphyseal cartilages, which are then converted into new bone

In thickness:
* osteoblasts in the periosteum of the bone deposit new bone on top of the old ones, increasing the thickness

Question 14

whick part of bone growth continues after adolescence

Answer 14

growth in thickness

Question 15

Long loop feedback control of GH secretion

Answer 15

• IGF-1 from liver increases GHIH secretion from hypothalamus
• IGF-1 directly inhibits GH secretion itself

Question 16

Short loop feedback of GH secretion

Answer 16

GH itself inhibts release of GHRH of hypothalamus

Question 17

Ultra short loop feedback of GH secretion

Answer 17

GHRH inhibts itself

Question 18

Factors stimulating GH secretion

Answer 18

• Starvation (Ghrelin)
• hypoglycemia
• protein rich meal (Arginine AA)
• Exrecise
• stress (symp)
• first 2 hours of deep sleep
• Sex hormones

Question 19

Factors inhibiting GH secretion

Answer 19

• increase blood glucose
• increase FFA
• Obesitiy
• Aging
• Rise in cortisol (glucocorticoid) levels (chronic)