Week 3 - hormones Flashcards
(19 cards)
what is long loop feedback?
hypothalmic/ pituitary hormones are inhibited by the target gland hormone
what is short loop feedback?
where an anterior pituitary hormone inhibits the release of its associated hypothalamic hormone
what is ultra short loop feedback?
secretion of the hypothalamic hormone is inhibited by that same hormone
what is humoural stimuli?
regulates hormone secretion
eg, when Ca++ levels increase, TG releases calcitonin but if Ca++ levels decrease PTG releases PTH
peptide and protein hormones?
synthesized as preprohormones
stored in vesicles
circulate in blood unbound
hydrophilic and signal through transmembrane receptors
steroid hormones?
derived from cholesterol
lipophilic
transported in blood bound to transport proteins
catecholamines?
derived from tyrosine
stored in vesicles
unbound or loosely associated with proteins in blood
hydrophilic and signal through GPCR
thyroid hormone?
derived from iodination of thyronines
lipophilic, stored in thyroid follicle by covalent attachment to thyroglobulin
tightly bound to proteins
signal through nuclear hormone receptor family
what is the initial step in steroid biosynthesis and what enzyme catalyzes this?
cholesterol to pregnenolone by cytochrome P450
what happens when there is a mutation in the 25-hydroxylase enzyme?
cortisol production is inhibited and sex steroid production increases
what are hormone binding proteins? examples.
plasma proteins which help the transport of hormones in the blood
eg, thyroxine, testosterone, cortisol
how are hormones cleared from the body?
excretion by liver into the bile
excretion by kidneys into the urine
degraded by the target cell after binding to receptors
which hormones are secreted before bed?
prolactin and GH
which hormones peaks in the morning?
cortisol
what is down regulation?
increased hormone concentration and increased binding with its target cell receptor sometimes cause the number of active hormone receptors to decrease
what is up regulation?
increased affinity and increased number of receptors = increased response due to a low concentration of hormone
what is permissiveness?
facilitation of one hormone action by another
eg, hormone A must be present for the full strength of hormone Bs effect
what is synergism?
when the actions of several hormones are complementary and their combined effect is greater than separate
eg, FSH+ testosterone=increased sperm
Insulin and growth hormone act synergistically to stimulate insulin-like growth factor-I production
mechanism of action for epinephrine?
in liver GPCR, converts glycogen to g6p and to glucose
