Physiology: Growth Hormone
What are the direct effects of growth hormone?
1. Decreases fat mass 2. Increases glucose production, release at liver 3. Increases protein synthesis in muscle
How can you measure the number of Growth Hormone Receptors at target tissues?
By measuring Growth Hormone Binding Protein (GHBP) because it is a cleaved derivative of GH Receptors.
Acromegaly
Caused by excess secretion of Growth Hormone after closure of epiphyses. Usually caused by GH-secreting pituitary tumor. Increase in facial structures, hands, feet, deepening voice. Soft tissue swelling of internal organs
Gigantism
Causes by excess production of growth hormone in childhood before epiphyses close Often due to pituitary tumor.
What protein does Growth Hormone bind to in plasma?
Growth Hormone Binding Protein (GHBP)
Contrast IGF-1 & IGF-2.
IGF-1 is the primary functional IGF after birth. IGF-2 is important in fetal development. It is present in higher concentrations than IGF-1 in adults
Contrast the IGF-2 and IGF-1 receptors.
IGF-1 receptors binds both IGF-1 and IGF-2. It's found everywhere except the liver. IGF-2 receptors bind IGF-2 more than IGF-1.
Where is somatomedin (IGF-1) secreted?
Liver
What mediates the indirect effects of Growth Hormone?
Somatomedin (IGF-1)
Name 5 factors that stimulate growth hormone secretion.
1. Hypoglycemia 2. Protein deficiency 3. Exercise 4. Trauma 5. Peaks during sleep (GH is involved in bringing blood glucose back up)
What are the indirect effects of growth hormone?
1. Increases growth of non-muscle cells
What is the half life of Growth Hormone? How is the half-life increased?
10-30 minutes It is bound to growth hormone binding protein, increasing the half life to 12-16 hours.
Approximately how much Growth Hormone is protein bound?
50%
Pituitary Dwarfism
Deficiency of anterior pituitary Growth Hormone secretion during childhood or failure of IGF-1 generation or action (African pygmy) Treatable with replacement therapy
What is the major IGF Binding Protein in circulation?
IGFBP-3
What is somatomedin?
Insulin-like Growth Factor-1 (IGF-1)