how does the hypothalamus-pituitary axis work?
releasing hormones from hypothalamus stimulate pituitary to release trophic hormones which stimulate peripheral glands to produce and release their hormones.
what is the difference between the anterior and posterior pituitary gland?
anterior pituitary secretes trophic hormones (hormones that stimulate other organs to secrete hormones) while posterior secretes hormones that don't need to stimulate another organ (ie: oxytocin and ADH).
name some trophic hormones that are released from the anterior pituitary.
FSH, LH (gonadotrophic hormones), TSH (thyroid stimulating hormone), ACTH (adrenocorticotropic hormone)
what stimulates growth hormone (GH) release?
hypoglycemia, fasting, starvation and stress. the hypothalamus releases GHRH (growth hormone releasing hormone) which stimulates the anterior pituitary to release GH.
what inhibits growth hormone (GH) release?
increased glucose levels, free fatty acid release in the blood, obesity, cortisol, and a hormone called somatostatin released by the hypothalamus
growth hormone stimulates production of IGF. what are some functions of IGF-1?
IGF-1 is a hormone produced by the liver. it increases protein synthesis which increases 1) bone and cartilage growth 2) body organ growth 3) lean muscle mass.
how does growth hormone exhibit anti-insulin effects?
increases breakdown of fats (lipolysis) with increased use of free fatty acids (FFA) for fuel. it also increases carbohydrate metabolism which increases blood glucose levels but prevents glucose from being taken up by fat/muscle cells for storage/fuel.
pituitary tumors or agenesis (incomplete development) of pituitary causes GH deficiency. why?
pituitary does not produce GH
growth hormone excess ( adult)
acromegaly (enlargement of soft bones in hands and feet and in the face)
how does the hypothalamus stimulate release of gonadotropins by the pituitary?
GnRH (gonadotropic releasing hormone)
autoimmune disorder where the thyroid is destroyed (symptoms may be the same as hypothroidism). major cause of goiter and predominantly disease of women.
Graves disease manifestations
goiter, fine hair, sweating, tachycardia, weight loss, oligomenorrhea (few periods), tremor
what does ACTH do, and where is it secreted from?
it stimulates the adrenal cortex to secrete various hormones (ie: cortisol), is secreted from the anterior pituitary
what components make up major adrenal cortical hormones?
cholesterol and acetate. they are corticosteroids.
stimulates protein breakdown into amino acids -> amino acids are transported to liver -> liver produces glucose from amino acids
more cortisol functions
1) catabolism increased (muscles, free fatty acids, glucose), stimulates sympathetic nervous system 2) immune system suppression 3) increase plasma proteins
Addison's disease manifestations
hyponatremia, hypoglycemia, decreased cardiac output (bc of hypovolemia due to high sodium and water output), hyperkalemia, nausea, vomiting, weight loss, anorexia, lethargy
which disorders arise from excessive adrenal secretion?
Cushing's syndrome (glucocorticoid hormone excess)
Cushing's syndrome manifestations
muscle weakness, thin extremities, problems with glucose metabolism which may cause diabetes, immune suppression
secondary adrenal cortical insufficiency
caused by hypopituitary or removed pituitary gland. could also occur because cortisol was administered (inhibiting the pituitary).
acute adrenal crisis
usually a sudden flare up of Addison's disease which causes severe adrenal insufficiency. symptoms are the same as Addison's.
oversecretion of aldosterone (which would cause hypernatremia, hypokalemia, hypervolemia)