Hormonal control of growth Flashcards
Growth hormone
191 aas
secreted by the anterior pituitary in a pulsatile manner under the control of its hypothalamic releasing hormone (GHRH)
carried in plasma in free form and by GHBP
most of action is mediated through insulin-like growth factor-1 (IGF-1)
most effective in episodic bursts than at sustained levels
GHBP
produced by the liver
stimulated by binding of free GH to receptors on liver
Ghrelin
secreted by stomach –> hunger
acts on pituitary to stimulate release of GH
Somatostatin (SS)
inhibition of GH secretion
secreted by hypothalamus
acts on anterior pituitary
IGF-1
produced by action of GH in all tissues containing GH-receptors
acts locally/paracrine
about 99% of plasma IGF-1 is protein bound
function: stimulate growth in both skeletal and soft tissues
increase in plasma IGF-1 suppresses GH secretion
GH-IGF-1 axis
negative feedback of plasma IGF-1 on GH secretion
Hormones essential for GH stimulated growth
Gonadal hormones
Thyroid hormones
Causes of dwarfism
Congenital failure of GH production (classical), treat with GH
congenital absence of peripheral GH receptors (Laron dwarfism)- treat with IGF-1
IGF-2
stimulates pre-natal growth
Investigation of short stature
rule out endocrinopathies neurology: rule out hypothalamic disease/trauma nutritional gastrointestinal-malabsorption syndromes cytogenetic abnormalities
Insulin stress test
investigation of GH deficiency
measure IGF-1 level
measures the function of the pituitary gland
blood is drawn for measurements of glucose and GH levels before injection, 30 min, 60, 90, and 2 hours after.
GH reference interval
fasting 4 ug/L
abnormal: no peak after stimulation
Growth hormone excess leads to:
gigantism in children
acromegaly in adults
Screening for acromegaly
single level of IGF-1
lack of suppressoin of GH level after glucose supplementation
