Regulation of Growth Flashcards
What does growth depend on?
genetic determination
an adequate diet
freedom from chronic disease and stress
normal levels of growth influencing hormones
What are the hormones regulating growth?
TH - hypothyroid children stunted
Insulin - deficiency blocks growth, hyper spurs growth
Testosterone - pubertal growth spurt, depends on presence of GH
Estrogens
GH
IGF-1
Calcitonin, PTH and Vit D
What are the growth stages ?
prenatal
growth in infancy
adolescence
What regulates prenatal growth?
maternal factors, fetal insulin and IGF
What regulates growth in infancy?
genetic factors, GH production, TH, IGF
What regulates growth in adolescence?
GH, Insulin, IGF and sex hormone surge
How much GH is circulating a day?
500microg
What is the half life of GH?
25-30mins
What is GH also known as?
somatotropin
How is growth hormone regulated in the hypothalamus?
GHRH and GHIH
What does GH stimulate in the liver?
IGF
What is the signalling pathway which results in GH release?
GHRH binds the receptor -> Gas -> cAMP -> PKA -> CREB -> synthesis of Pit-1 mRNA -> Pit-1 TF -> synthesis of GH mRNA -> GH synthesis and release
What is the signalling pathway which releases IGF -1 ?
GH - binds 2 receptors -> JAK tyrosine kinase -> STAT transcription factor -> gene expression of IGF-1
What are the direct effects of GH?
stimulates growth - hypertrophy - increases size and volume of cells - bone thickness
stimulates cell reproduction - hyperplasia - increase no. of cells - bone length
What is the effect of GH on metabolism?
stimulates cell metabolism
increases protein synthesis
increases fat breakdown for energy
carbohydrate metabolism changes
How does GH affect carbohydrate metabolism?
decreased use of glucose for energy
increased glycogen deposition
increased blood glucose levels
increase insulin secretion
what are the negative feedback mechanisms for GH?
high levels of IGF-1 stimulates GHIH
high levels of GH inhibits GHRH
what are the negative feedback mechanisms for GH?
high levels of IGF-1 stimulates GHIH
high levels of GH inhibits GHRH
When is GH released at most?
pulsatile release, most during sleep
What stimulates GH secretion?
exercise, stress, fasting, amino acids
What inhibits GH secretion?
high glucose
What responses does IGF-1 stimulate?
linear bone growth and cell proliferation leading to soft tissue growth
What do IGFBPs do?
bind circulating IGF with high affinity and specificity
What are the functions of IGFBPs?
act as carriers of IGF in the plasma
prolong the half life of IGF in circulation
regulate IGF access to receptors in ECF
What is the most abundant form of IGFBP?
IGFBP 3
What are the functions associated with IGFBP 3 and IGFBP 1?
IGFBP3 stimulates growth stimulation
IGFBP 1 inhibits growth
