Growth hormone & insulin like growth factor Flashcards
what hormone stimulates the release of growth hormone ?
Growth hormone relasing hormone (GHrH) produced by the hypothalamus
what type of cell in the anterior pituitary gland secretes growth hormone?
somatotrophs
what are different stimuli of GH release?
- exercise - promotes GH secretion
- low blood glucose (hypoglycaemia) - promotes GH secretion
- increase in amino acids in blood - promotes GH
- age - there is a normal age decline in GH
what is the pulsatile & circadian secretion of GH?
- pulsatile - regular pulses at 3-4 hour intervals
- circadian - peak secretion coincides with with onset of deep sleep (REM4)
where does bone elongation occur?
- bone elongation occurs at the epiphyseal growth plate (cartilage)
in relation to** chondrocytes (cells that produce cartilage), what is the role of GH and IGF-I?**
- they increase** differentiation and proliferation **
Describe the growth hormone sigalling pathway
the JAK-STAT pathway
- GH binds to GH receptors and causes a conformational change &** activates JAK proteins**
- The JAK proteins phosphorlyate the GHR cytoplasmic domain on tyrosine residues
* STATs dock onto the GHR receptor and the JAKs phosphorlyate them - STATS then dissociate from receptor and dimerise via their SH2 domain
- STATS translocate to the nucleus, bind to DNA and other regulatory proteins and activate gene transcription
what are the 2 major **metabolic functions/actions **of GH?
- increases plasma glucose levels by inhibiting glucose uptake in adipose tissue & skeletal muscle
- increases lipolysis in adipose tissue -increases ciruclating fatty acid
What is insulin like growth factor?
- extension of growth hormone
- once growth hormone reaches liver, IGF-I is produced
- acts a lot like insulin
what are the metabolic actions of IGF-I?
- increases glucose uptake / utilisation in skeletal muscle
- increases protein synthesis in skeletal muscle
- increases** insulin sensitivity**
- decreases GH secretion - through negative feedback mechanism
what is congenital GH deficiency?
what is it? causes? treatment?
- reduction in growth hormone & insulin like growth factor
- causes may be birth trauma (eg hypoxia) or mutations in transcription factors that control pituitary differentitiation
- treatment involves GH replacement therapy
what can acquired growth hormone deficiency** arise from** in children?
- trauma
- infections eg meningitis
- systemic diseases eg leukemia
what are examples of** GH deficiency symptoms i**n children?
- short height
- delayed tooth devlopment
- delayed onset of puberty
-
increased amount of fat around waist
* low growth velocity for age/ pubertal stage
What is** GH resistance- laron dwarfism** ?
type of disorder, high or low GH & IGF?, characteristics & treatment
- autosomal recessive disorder
- GH receptor deficiency
- high GH and low IGF
- characteristics include - short height, hypoglycemia, poor muscle development
- treatment - IGF
what is adult onset GH deficiency?
causes, features treatment
- causes - pituitary tumours, head trauma, abnormalities in the hypophyseal circulation (anterior pit)
- **features **- psychological disorders, altered body comp (decrease in lean body mass, increase in adiposity/fat), metabolic abnormalites
*** treatment **- GH replacement therapy
