Normal Growth and Clinical Aspects

Question 1

What are the routes involved in the secretion and target effects of GH?

Answer 1

• GH is released from the anterior pituitary following stimulation by GHRH which is produced by the hypothalamus

Effects of GH:

• Necessary for growth and development in children (after 8-10 months), but also important in adults to maintain tissues and their energy supply
• GH stimulates cell size growth and cell division in target tissues
• GH effects bone by stimulating chondrocyte precursor cells to turn into chondrocytes, which produces IGF-1 which allows bones to grow through cartilage production
• GH increases gluconeogenesis
• GH reduces the effectiveness of insulin
• GH promotes the uptake of amino acids and protein synthesis in muscle, liver and adipose tissue

Question 2

What do the terms somatotrophin, somatostatin and somatomedin mean?

Answer 2

Somatotrophin - Growth promoting hormone

Somatostatin - Growth inhibiting hormone

Somatomedin - Another name for IGF-1 (it mediates/controls the effects of GH)

Question 3

What would happen to GH secretion following these events:

1 - Decrease in plasma glucose levels following and insulin injection

2 - Increase in plasma amino acids following a protein heavy meal

Answer 3

1 - A decrease in plasma glucose level will result in an increase in GH secretion (GH helps cells meet their energy requirements)

2- A rise in plasma amino acid levels will result in an increase in GH secretion (GH promotes protein synthesis)

Question 4

In what way can excessive GH secretion lead to diabetogenic symptoms?

Answer 4

GH has several actions which promote a rise in blood glucose levels:

• It stimulates gluconeogensis in the liver
• It reduces the effectiveness of insulin to stimulate glucose uptake by muscle and adipose tissue by actually releasing energy stores (anti-insulin effect)