Somatotropic Axis Flashcards
GH
- protein; t1/2 6-20 min
- most abundant APH (10x more)
Somatomedins
- several classes; IGF-1 to 7
- polypeptides w/ 40% homology to insulin
IGF-1
- systemic and autocrine effects
- low neonatally, high at puberty, lower later in life
- needed for skeletal & extra-skeletal development, adipocyte differentiation
IGF-2
- prominent during embryonic/fetal growth w/ insulin
The largest GH peak is about ________ after the onset of sleep
1 hr
_______ coded by the same gene as the GH-R
GHBP
GH secretion occurs as several large ________ or _______ each day, ___ to ____ in duration
Pulses; peaks; 10; 30
_________ is almost entirely bound to transport proteins
IGF-1
In older animals, GH and IGF’s remain essential regulators of ________________ and ______________
Tissue renewal; metabolism
Some IGF-1 transport/binding proteins have an ____________ function
Endocrine
________ and _______ act on the growth plate of long bones in children/young animals
GH; IGF-2
_____ promotes the growth of cartilage while _______ promotes the ossification (calcification) cartilage cells
GH; IGF-2
______ stimulates the synthesis and release of IGF-1 in many tissues, not just the liver
GH
*very difficult to differentiate b/w direct actions of GH and those of IGF-1
*both appear to exert opposite actions in some tissues — suggests that they do have independent roles!
Other physiological roles of GH
- Contributes to the maintenance and function of pancreatic islets
- Stimulates the immune system
- Anti-aging effects
- Stimulates the growth and regeneration of internal organs except for the brain
- Normal reproduction
GH can cross-react with ______
Prl-R
Commercial Applications of GH
- Increasing milk production, leaner cows
- Generation of transgenic salmon GH gene (overexpressed)
Problems with GH use
- increased animal stress (high milk production. & mastitis)
- adverse effects on reproduction (cystic ovaries, uterine disorders, decreased birth weight)
Gigantism
- Hypersecretion of GH before puberty
- GH influences IGF release from the liver and therefore stimulates extensive bone growth
- Usually caused by a tumor on the anterior pituitary gland
Acromegaly
- Most commonly affects “middle aged” individuals
- Hypersecretion of growth hormone after epiphyseal plate closure
- Can result in severe disfigurement
- In over 90% of acromegaly patients, the overproduction of GH is caused by a benign tumor of the pituitary gland (pituitary adenoma)
Dwarfism
- If GH is lacking, stunted or even halted growth may become apparent
- Children may grow slowly and puberty may be delayed by several years or indefinitely
- Dwarfism has no single definite cause:
• Mutations of specific genes
• Damage to the pituitary gland
• Turner’s syndrome
• Malnutrition
• Stress (psychogenic/psychosocial dwarfism - PSS)
