endo
- Created by: jo bill
- Created on: 20-12-14 14:32
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Growth hormones and factors
- process of growth is tightly regulated by a selection of hormones
- growth hormone (GH)
- insuli like groth factors (IGFs)
- insulin
- 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
- increases muscle amss
- increases protein synthesis
- stimulates organ growth
- increases bone mass
- maintains pancreatic islets
- stimulates immune response
- 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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