8. Growth hormone Flashcards

1
Q

What type of hormone is GH?

A

peptide

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2
Q

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

A

produced by ant.pit. somatotrope cells

  • stimulated by GHRH
  • inhibited by GHIH/somatostatin
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3
Q

Describe the pattern of GH release.

A

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

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4
Q

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

A
  • decrease in glucose/free FAs… increase GH secretion

- increase in glucose/free FAs… decrease GH secretion

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5
Q

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

A
  • fasting: increase GH secretion

- obesity: decrease GH secretion

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6
Q

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

A
  • surge in GH secretion after onset of deep sleep
  • light/REM sleep inhibits GH secretion
  • stress (e.g. trauma) and exercise increase GH secretion
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7
Q

How does negative feedback regulate GH secretion?

A
  • 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
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8
Q

What is the role of GH in adults and children?

A

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

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9
Q

What are the 2 ways GH affect target cells?

A
  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
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10
Q

Which organs produce IGF?

A

mainly liver (75%) and skeletal muscle

small amount from bone, kidney and CNS

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11
Q

How do IGFs circulate in blood?

A

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

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12
Q

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

A

IGF-1: mediates GH effects in adults

IGF-2: pre-natal growth and dev.

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13
Q

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

A

increased:

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

decreased:
- glucose uptake

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14
Q

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

A

in some tissue IGF-1 inhibits apoptosis

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