Endo: Pituitary Physiology (GH)

Question 1

Growth hormone is released by ___________ (cells) of the _______ pituitary.

Growth hormone is a ___________ hormone

Answer 1

Growth hormone is released by somatotrophs of the anterior pituitary

Growth hormone is a peptide hormone

Question 2

Describe GH’s signaling at the target cell

Answer 2

• GH is a peptide hormone, so it uses a cell surface receptor
• GH binds to a cytokine receptor, which activates JAK/STAT pathway
• same as prolactin

Question 3

Name the metabolic effects of Growth Hormone (4)

Answer 3

• Increases serum glucose levels (gluconeogenesis)
• Increases serum FFA levels (fat hydrolysis)
• Increases AA uptake by muscles and increases protein synthesis
• Blocks insulin activity

Question 4

How does Growth Hormone induce growth?

Answer 4

• GH makes energy available (via metabolic effects) and stimulates IGF production (insulin-like growth factor)
• IGF causes bone and muscle growth

Question 5

How does the hypothalamus regulate GH release from pituitary? (3)

Answer 5

• GHRH (released by hypothalamus) stimulates GH release by pituitary
• SST (released by hypothalamus) inhibits GH release by pituitary
• Excess GH increases SST release (negative feedback)

Question 6

What two factors stimulate GHRH release from hypothalamus?

Why?

Answer 6

• Hypoglycemia
  
  • GH will increase serum glucose
• Elevated serum AA’s
  
  • GH will cause muscle to take up and use AA’s

Question 7

Describe the production of IGF with a normal diet

Answer 7

With a normal diet,

• Glucose causes insulin release
• AA’s cause GH release
• Presence of both insulin and GH allows for IGF production
• IGF induces growth

Question 8

Describe the production of IGF under starvation

Answer 8

With starvation,

• There is low glucose and low AA’s
• Low glucose stimulates GH release
  
  • GH increases serum glucose
• Low glucose suppresses insulin
  
  • Without insulin, no IGF is produced
• No induction of growth

Question 9

Describe the two syndromes of excess growth hormone (5)

Answer 9

• Gigantism
  
  • Increased GH during puberty, so get increased long bone growth
  • Pts are very TALL
  • Complications due to diabetes and cardiovascular disease
• Acromegaly
  
  • Increased GH post-puberty, when long bones are fixed in length
  • Pts have large hands, feet, head

Question 10

Compare hormone levels in dwarfism, laron’s dwarfism, and African pygmies

Answer 10

• Dwarfism
  
  • Low GH, leading to low IGF
• Laron’s Dwarfism
  
  • Normal/high GH but low IGF
  • GH non-functional
• African Pygmies
  
  • normal GH and IGF
  • IGF non-functional