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Growth hormones and factors

  • process of growth is tightly regulated by a selection of hormones
  1. growth hormone (GH)
  2. insuli like groth factors (IGFs)
  3. insulin
  4. other factors 

hypothamamic involvement

  • hypothalamus regulates the system from the top by releasing stimulatory and inhibitory releasing factors

Growth Hormone Releasing Hormone (stimulatory, somatocrinin)

  • 44 amino acid peptide hormone 
  • produced in acruate nucleus of hypothalamus
  • released from neurosecretory terminals of acruate neurones in pulsatile fashion
  • transported via the hypothalamic -hyphysial 
  • anterior pituitary glans
  • binds the GHRH receptor

Growth Hormone Inhibiting Hormone (inhibitory, somatostatin SRIF)

  • peptide hormone with 2 active forms
  • formed from cleavage of a pre-protein 
  • produced in periventricular nucleus from the hypothalamus
  • released from parvicellular neurones at median eminence and also trnsported via the hypothalamic-hyposial portal system to the anterior pituitary gland
  • binds to the GHRH receptor
  • release is regulated by high levels of GH and IGFs
  • 5 receptors - 1,2,3 and 5 expressed in pituitary
  • produced in other areas of the body, where its release regukates peripheral functions

growth hormone

  • 191 amino acid peptide hormone
  • secretion ^ in first 2h of sleep
  • ciculates bound to specific plasma proteins
  • have -ve feedback on its own production
  • has many physiological effects
  1. increases muscle amss
  2. increases protein synthesis
  3. stimulates organ growth
  4. increases bone mass
  5. maintains pancreatic islets
  6. stimulates immune response
  7. hepatic effects ( adults - protein synthesis, wound healing, prevention of osteoporosis)

metabolic effects of GH

  • GH has a role in metabolism, dependent on level of exposure
  • acutely - insulin-like effects ( ^ glucose uptake, ^amino acid uptake, ^lipogenesis by muscle and fat)
  • chronically - antiinsulin effects ( ^lipolysis, v glucose uptake)
  • chronic GH excess can lead to type 2 diabetes

GH and the liver

  • GH binds to receptors on hepatocye membrane
  • tyrosine kinase receptor (JAK/Stat) Stimulates the hepatocyte to synthesise and release two other groth factors (IGF-I, IGF-II)

IGF-I

  • peptide hormone -70 amino acides
  • secreted as soon as it is produced 
  • circulates bound to binding proteins
  • IGF-2 > IGF-! in circulation
  • bind to IGF1R (tyrosin ekinase receptor)
  • GH can sensitise cells to IGF-!
  • IGF-1 has a -ve…

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