Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
19 Cards in this Set
- Front
- Back
How is GH secretion regulated?
|
1. GH secretion is pulsatile and episodic
2. GH secretion is enhanced by: > exercise > stress > sleep (stages 3 and 4) > postprandial decline in glucose levels > increase in specific amino acids 3. GH secretion is inhibited by > postprandial hyperglycaemia > free fatty acids |
|
What does postprandial mean?
|
Time after any meal
|
|
Describe GH secretion across life.
|
- Very high in mid-fetal life (up to 150ng/mL)
- 30ng/mL in cord blood - 5-10ng/mL in children - 2-5 ng/ml in young adults - low in old age |
|
What are the actions of GH?
|
- GH acts at specific GH receptors
- The biological activity of GH is regulated by a GH binding protein which is formed from the extracellular domain of the GH receptor - The actions of GH are often mediated via a second molecule known as somatomedin, or more usually as IGF-1 - The actions of GH are anabolic and anti-catabolic, resultin gin increases in protein synthesis |
|
Give a summary of the GH mechanisms of action.
|
- Direct Anti-insulin effects
> increased lipolysis > increased glucose mobilization - Indirect growth promoting effects > increased cartilage formation > increased long bone growth > increased protein synthesis |
|
Describe IGFs and Feedback.
|
- Indirect effects of GH are mediated by somatomedins
- Mostly IGF1 postnatally - GH stimulate IGF1 production by > liver (endocrine mechanism) > GH target tissues (paracrine mechanism) - IGF1 is bound in blood to one of 6 IGFBPs - IGF1 feedback inhibits GH release at > anterior pituitary > hypothatlamus |
|
What is the somatomedian hypothesis?
|
Indirect actions of GH
- GH alone does not stimulate cell growth in vitro stimulates secretion of IGFs which do. - The somatomedins: IGF-1 and -2 - Skeletal actions of IGFs at growth plate - IGF receptors - IGF binding proteins - Laron Dwarfism - GH |
|
How does growth occur?
|
Hypertrophy
Hyperplasia Matrix deposition (extracellular) Protein/DNA ratio |
|
What are the inputs to growth?
|
Heredity
Nutrition Endocrine regulation General health Intrauterine growth retardation Emotional deprivation and psychological factors |
|
How is growth assessed?
|
Careful history and examination
Consideration of all possible contributors Use of growth charts Biochemical and imaging assessment |
|
Describe how history is used in growth assessment.
|
- IUGR
- Systemic disorders (esp small bowel disease) - Evidence of skeletal, chromosomal abnormalities - Endocrine status - Dietary intake and drugs (glucocorticoids - asthma) - emotional, psychological, family and school |
|
What is the link between thyroid hormones and growth?
|
- Thyroid hormones needed for setting metabolic rate
- Also for differentiation > brain - cretinism occurs in thyroid hormone deficient babies > skeletal maturation - Deficiency > growth retardation. Responds to therapy - catch-up growth - Permissive actions - needed for GH action. - Stimulates GH secretion |
|
What is the link between Sex steroids and growth?
|
- Adrenarche-androgen secretion increases age 6-8, regulated by ACTH. (mainly DHEA)
- Patterns of growth at puberty > first distal - hands and feet > then arms and legs > then trunk - Testosterone (DHT) actions > linear, wt growth, muscle mass > interactions with GH |
|
What is the link between estrogens and growth?
|
Estrogens:
> tissues exquisitively sensitive to E2 > At v. low concentrations, stimulatory > At high concs, inhibitory - Androgens and estrogens promote epiphyseal fusion, terminating adolescent growth spurt - both stimulate GH secretion |
|
What is the link between glucocorticoids and growth?
|
- Inhibit growth
> all tissues except gonads > direct action > protein catabolism (anti-GH), N excretion - Causes of corticoid excess in children > adrenal tumour > cushing's disease > excess therapy for anti-inflammatory effects |
|
What is the link between Insulin and growth?
|
- Insulin deficiency in childhood (IDDM)associated with growth retardation
- Growth restored with insulin Rx - Probably acts via IGF-1 receptor (homologous to insulin receptor) - Leprechaunism due to insulin receptor defects. Children are born very small and stay below normal size. |
|
What happens with GH Excess and deficiency?
|
GH excess
- in children causes gigantism - in adults causes acromegaly GH deficiency - in children cause dwarfism - in adults causes decreased bone density and muscle strength |
|
What can occur with giantism?
|
Carpal tunnel syndrome.
|
|
What are some types of dwarfism?
|
- Idiopathic GH deficiency
- Laron dwarfism |