1.3 Endocrine Regulation of Growth

Question 2

What is/isn’t the definition of growth?

Answer 2

• Progressive increase in the size of an organism, requiring net synthesis of proteins
• NOT increase in mass associated with fluid retention

Question 3

How does the predominance of certain hormones during growth change from foetal/infancy/childhood/puberty?

Answer 3

Foetal: IGF-1 and 2
Infancy: GH and thyroxine
Childhood: GH-IGF-1 axis and thyroxine
Puberty: androgens added in

Question 4

Why might somatostatin be released by the pancreas (hint: what’s detecting it?) What effects might it exert on the endocrine pancreas itself?

Answer 4

• Inhibits the release of pancreatic hormones
• Therefore, can be triggered by insulin when blood sugar is low, and triggered by glucagon when blood sugar is high

Question 5

This cell type makes up about half of all cells in the anterior pituitary…

Answer 5

Somatotrope (cells that release Growth Hormone)

Question 6

Role of IGF-1 vs IGF-2

Answer 6

IGF-1: Exerts effect on most tissues in body (stimulates cell growth, inhibits apoptosis)

IGF-2: Promotes growth during gestation

Question 7

List some factors that can increase secretion of growth hormone

Answer 7

• Decreased blood sugar
• Sleep
• Exercise
• Stressors / excitement / trauma (of certain levels)
• Increased blood amino acids (GH will pull them into muscle)
• Grehlin release

Question 8

What is grehlin? When is it released?

Answer 8

• Grehlin is a hormone
• It is released in response to an empty stomach; sometimes called “hunger hormone”

Question 9

Which negative feedback loops/factors might decrease GH release?

Answer 9

• High somatomedins/GH
• High blood sugar
• High blood fatty acids
• Obesity

Question 10

List as many actions of somatomedins as you can think of

Answer 10

• Hypertrophy + hyperplasia
• Interstitial bone growth
• Increased protein synthesis
• Epiphyseal plate proliferation

Question 11

List as many actions of GH as you can think of

Answer 11

• Amino acids pulled into muscle
• Gluconeogenesis
• Lipolysis
• Increased blood sugar

Question 12

What is the receptor type of GH receptors? What is the outcome of this similar to?

Answer 12

• JAK/STAT receptors
• Outcome is altered gene transcription (and therefore protein synthesis)
• Similar in outcome to steroid receptors (but extracellular)

Question 13

Acromegaly vs gigantism

Answer 13

Both involve hypersecretion of growth hormone.

If in childhood; bone keep growing in proportion length-wise, so this results in gigantism (Yao Ming). Also increased risk of diabetes (high blood sugar, insulin resistant)

If after childhood; body resorts to appositional growth, so this results in thickening of bones and acromegaly (like Grawp)

Question 14

How is acromegaly/gigantism treated?

Answer 14

• Somatostatin analogues (decrease GH)
• Surgery to remove tumour on anterior pituitary

Question 15

Why can negative psychological factors decrease GH release?

Answer 15

• The hypothalamus is circumventricular (exposed to substances outside the blood brain barrier)
• Therefore, if stress hormones are high, can damage hypothalamus
• In this case, less ability to produce GHRH; therefore less GH release

Question 16

True or false: GH and IGF-1 are global, and the only true growth factors in the body

Answer 16

• False
• There can also be local growth factors, such as those in the nerves, or epidermis