GROWTH HORMONE-1

GROWTH HORMONE-1 - GROWTH HORMONE (GH) = Somatotropin ....

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GROWTH HORMONE (GH) = Somatotropin Growth hormone is a 191 amino acid polypeptide hormone released by the somatotrophs in the anterior pituitary. Children release 1,600ug-1,800ug/day Adults release 400ug/day Plasma half-life is 20min-50min .
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Growth hormone release declines with age
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Factors that affect Growth hormone release Factors that increase growth hormone levels : Increased GHRH secretion SLEEP – 70% of daily GH secretion occurs during the 3 rd and 4 th stages of sleep Stress – emotional, physical, exercise, trauma, surgery Metabolic factors – hyperaminoacidemia, hypoglycemia Anorexia nervosa and starvation – result in hypoglycemia Dopamine agonists Chronic renal failure – due to the absence of negative feedback by IGF Factors that decrease growth hormone levels Increased Somatostatin (GHIH) secretion Hyperglycemia Hyperlipidemia – high levels of fatty acids Obesity – due to persistent hyperglycemia and Hyperlipidemia Severe emotional deprivation Dopamine antagonists Paradoxically, dopamine agonists SUPPRESS growth hormone levels in acromegaly
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Figure 16.7
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Biological Actions of Growth Hormone Growth hormone binds to growth hormone receptors that recruit Tyrosine Kinase (JAK/MAPK/STAT signal transduction pathway) Biological actions may be DIRECT and INDIRECT DIRECT biological actions of GH : - GH stimulates lipolysis; GH is a lipolytic hormone - GH inhibits cellular uptake of glucose resulting in increased blood glucose levels = GH is an insulin antagonist GH is a diabetogenic hormone – GH increases blood glucose levels by preventing cellular uptake of glucose , - GH stimulates the production of IGFs (Insulin-like Growth factors) by hepatocytes INDIRECT biological actions of GH : - GH stimulates the production of IGF-1 and IGF-2 which then stimulate postnatal longitudinal bone growth ( IGFs stimulate proliferation of cartilage in epiphyseal plates) and growth of the organs . Growth hormone (via IGF) synergizes with sex steroid hormones to cause adolescent growth spurt . - stimulates cellular uptake of amino acids and protein synthesis Hence, the growth-promoting effects of GH are indirect ( via IGF actions)
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Abnormal Growth Some causes of short stature: - Hypothalamic dysfunction - hyposecretion of GHRH - Pituitary dysfunction – GH deficiency in childhood results in dwarfism - GH receptor insensitivity – Laron’s dwarfism
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This document was uploaded on 10/27/2011 for the course BSCI 447 at Maryland.

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GROWTH HORMONE-1 - GROWTH HORMONE (GH) = Somatotropin ....

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