endocrine control of growth Flashcards
How do growth hormones get released?
Neuronally activated through posterior pituitary
Endocrine release of hormone
Hormone released from anterior pituitary
What happens if you get growth of pituitary gland (tumour)?
Optic chiasma there
Compression of peripheral visual field
Compression of optic nerve- reduction in precision of vision
Loss of colour perception
What is acromegaly?
Middle age
Growth hormone released can act of proliferating cells- coarsening of features
Doesn’t affect long bones
Why might extra growth hormone be released?
Benign tumour of pituitary gland
Tumour elsewhere with pituitary like features
How does growth hormone work?
Directly on cells eg. Osteoblasts
Indirectly eg. Liver releases IGF-1
IGF-1 tends to have negative feedback on growth hormone release
Levels tend to fluctuate throughout day, goes up after eaten, tends to have diurnal rhythm
How does oestrogen work?
Increased growth hormone secretion
Important in developing bone density
Direct and indirect action
Bimodal dose dependent phenomenon
Growth hormone affects pubertal growth spurt
Affects programmed senescence in growth plate
How does androgen work?
Cells around periphery of bone possibly have greater activity of androgens to make bone thicker
How does muscle grow?
Growth hormone acts via IGF-1 for myofibril proliferation
Usually proportionate to body size
Little evidence that growth hormone promotes hypertrophy at reasonable dosage
Paracrine IGF-1 has role in load-induced hypertrophy
Can growth hormone give performance enhancement?
Positive effect on c. tissue strength (if working at limit of loading muscles- won’t tear tendons/ligaments)
Reduce recovery time- anticatabolic (stops breakdown of body tissues)
Increase VO2 max
How do glucocorticoids modulate growth hormone?
Increases growth hormone secretion
Affects SST and GHRH release
Chronic exposure reduces growth hormone release
Chronic juvenile arthritis- corticosteroids given to dampen immune response but likely to reduce growth
Adults- reduced growth hormone- risk of osteoporosis, protein loss and raised serum lipids
~chronic glucocorticoid use mitigated by recombinant growth hormone leading to glucose intolerance
How is growth hormone diabetogenic?
Promotes gluconeogenesis, glugogenolysis, lipolysis
Insulin released to compensate
Long term- insulin resistance
How is insulin an IGF-1 homologue?
Insulinopenia reduced children’s growth
Obese boys (high insulin) are taller
~the insulin can act at growth plates like IGF-1
