Growth Hormone

Question 1

What are the hormones responsible for the regulation of growth.

Answer 1

• Thyroid hormone
• Insulin
• Testosterone/Estrogen
• Growth hormone (somatotropin)
• Insulin like growth factor (most important)
• Calcitonin/PTH/VD

Question 2

What is the metabolic effect of growth hormone?

Answer 2

• The receptor which binds GHRH is a GPCR, when binding occurs the g-protein (g-alpha) is coupled to adenylate cyclase to produce cAMP.
• cAMP aids CREB into the nucleus to alter gene expression. PIT-1 acts on this converting it into growth hormone.

Question 3

Describe the mechanism of action of GH.

Answer 3

• GH binds to 2 GH-Rs which activates the JAK-STAT pathway leading to the expression of IGF-1 gene.
• IGFBP (binding protein) is the main carrier of IGF-1 in the plamsa.
• This leads to hypertrophy and hyperplasia (bone lengthening).
• GH also increases AA synthesis while reducing protein and fat breakdown.

Question 4

Briefly describe the negative feedback loop.

Answer 4

• High levels of GHIH/SS decrease secretion of GH while high levels of GH inhibit GHRH.

Question 5

What are some conditions linked to abnormalities in GH?

Answer 5

• Dwarfism: Caused by deficiency in GH, normally occurs in childhood when GH is absent during development. May also be caused due to mutations in GHRH or PIT-1,
• Gigantism: Caused by continuous secretion of GH, epiphyseal plates are still open and GH aids in longitudinal growth of long bones. May also be caused by a pituitary adenoma which secretes excess Gh/IGF-1.
• Acromegaly: After epiphyseal plates have sealed resulting in lateral growth (bone width)