8. Growth hormone

Question 1

What type of hormone is GH?

Answer 1

peptide

Question 2

By which cells is GH produced and how is this regulated?

Answer 2

produced by ant.pit. somatotrope cells

• stimulated by GHRH
• inhibited by GHIH/somatostatin

Question 3

Describe the pattern of GH release.

Answer 3

pulsatile secretion with circadian rhythm and max. release late at night

Question 4

What is the effect of plasma glucose and free fatty acid concentration on GH secretion?

Answer 4

• decrease in glucose/free FAs… increase GH secretion

- increase in glucose/free FAs… decrease GH secretion

Question 5

What is the effect of fasting and obesity on GH secretion?

Answer 5

• fasting: increase GH secretion

- obesity: decrease GH secretion

Question 6

How does the CNS affect GH secretion via inputs to hypothalamus?

Answer 6

• surge in GH secretion after onset of deep sleep
• light/REM sleep inhibits GH secretion
• stress (e.g. trauma) and exercise increase GH secretion

Question 7

How does negative feedback regulate GH secretion?

Answer 7

• short loop: GH stimulates somatostatin release from hypothalamus
• long loop: IGFs
  • inhibit GHRH release from hypothalamus and action of GHRH in AP
  • stimulate release of somatostatin from hypothalamus

Question 8

What is the role of GH in adults and children?

Answer 8

childhood: increase growth rate of skeleton and skeletal muscle
adults: maintain muscle and bone mass
promote healing and tissue repair

Question 9

What are the 2 ways GH affect target cells?

Answer 9

1. acts directly by binding to GH receptor: cytokine receptor coupled to janus kinase (intracellular enzyme)
2. acts indirectly by inducing insulin-like growth factor (IGF-1 and -2) production though JAK stimulation

Question 10

Which organs produce IGF?

Answer 10

mainly liver (75%) and skeletal muscle

small amount from bone, kidney and CNS

Question 11

How do IGFs circulate in blood?

Answer 11

bound to specific binding proteins which modulate their availability to activate IGF Rs on target cells

Question 12

When do IGF-1 and IGF-2 have the most effect?

Answer 12

IGF-1: mediates GH effects in adults

IGF-2: pre-natal growth and dev.

Question 13

What are the effects of IGF-1 on adult cells?

Answer 13

increased:

• cell size (hypertrophy)
• cell number (hyperplasia)
• rate of protein synthesis
• rate of lipolysis in adipose tissue (fat)

decreased:
- glucose uptake

Question 14

Why do some types of tumour express abundant IGF-1 Rs?

Answer 14

in some tissue IGF-1 inhibits apoptosis