Exam 3- Endocrinology Overview Flashcards
what do endocrine cells do?
release hormones into interstitial fluid (not ducts)
where do hormones released into the interstitial go?
enter the blood or act locally
what regulates secretion of hormones?
neural mechanisms and feedback mechanisms
what are two examples of negative feedback mechanisms for hormonal secretion?
hypothalamic-pituitary-gonadal axis
glucose-sensitive insulin release
is negative or positive feedback with hormonal secretion more common in biological systems?
negative feedback is much more common
what are two examples of positive feedback on secretion of hormones?
estrogen-induced surge of luteinizing hormone (LH) preceding ovulation
oxytocin-induced contraction of uterus leading to parturition
what does the anterior pituitary synthesize, if anything?
many hormones
does the posterior pituitary synthesize hormones?
no, only releases ones from the hypothalamus
what are the three categories of hormones based on where they act relative to where they are produced?
classical hormones
local hormones
neurohormones
what releases neurohormones? where do they act?
neurons
across synaptic cleft
into blood stream and elsewhere (autocrine)
where do steroid and fatty acid hormones bind?
primarily intracellular receptors
what do the chemical and solubility properties of hormones influence?
cellular site of action
how they are stored/secreted
how they are transported
what are the four classes of hormones based on their chemical structure?
peptide and protein hormones
steroid hormones
fatty acid compounds
amino acid derivatives
how are hormones stored in granules released?
Ca2+-dependent exocytosis
what are steroid hormones formed from?
cholesterol
what hormones are derived from Tyrosine?
thyroid hormone
catecholamines
what hormones are synthesized from Tryptophan?
serotonin
melatonin
what are eicosenoids?
lipid-soluble, local signaling molecules synthesized from fatty acids (usually arachidonic acid) in cell membranes
what non-specific transport proteins are synthesized in the liver?
albumin
prealbumin
thyroid hormones
what specific transport proteins are synthesized in the liver?
corticosteroid-binding globulin (CBG)
vitamin D-binding globulin (DBG)
thyroxine-binding globulin (TBG)
sex hormone-binding globulin (SHBG)
are hormones biologically active when bound?
no
why is binding of hormones to transport proteins important?
serves as reservoir of hormones to draw from
stabilizes free hormone levels (“buffers”)
increases lifespan of hormones in blood
how are peptide hormones and catecholamines eliminated?
enzymatic degradation and excretion in urine or bile
degrade intracellularly after binds
what organ eliminates steroid hormones and thyroid hormones?
kidneys: liver converts to water soluble compounds by conjugating with glucuronic acid
what/where are endocrine cells?
discrete glands
cells within organs or tissues that have other functions
neuroendocrine cells
immune cells
what happens when hormone levels are low in negative feedback?
secretion of hormone is stimulated
true/false: the posterior pituitary and the anterior pituitary are endocrine glands
false: only anterior pituitary is endocrine gland
posterior pituitary releases hormones from hypothalamus
where do peptide and protein hormones bind?
cell membranes
what is the classical protein synthesis biosynthetic pathway?
gene transcribed to mRNA (nucleus)
mRNA to preprohormone (cytoplasm)
signal peptide removed to make prohormone (ER)
secretory vesicles, proteolytic enzymes cleave to make hormone (Golgi)
Ca-dependent exocytosis of secretory vesicles
where does the synthesis of steroid hormones take place?
adrenal cortex
gonads and corpus luteum
placenta
what are the steroid hormones?
cortisol
aldosterone
estradiol
progesterone
testosterone
1, 25-dihydroxycholecalciferol
how are eicosenoid effects mediated?
G-protein coupled receptors
what groups are eicosenoids?
prostaglandins
prostacyclins
thromboxanes
leukotrienes
true/false: water soluble hormones can circulate free, but lipid-soluble hormones must be bound to water soluble transport molecules
true
what does an increase in binding protein lead to with the hormone levels?
initial decrease in free
feedback mechanisms will lead to increased secretion of hormone
how are lipid-soluble hormones eliminated?
broken down inside target cells after binding to receptors
how are steroid and thyroid hormones eliminated?
converted to water-soluble by liver with glucuronic acid, eliminated by kidneys
what are the five categories of mechanism for hormone action?
adenylyl cyclase mechanism (cAMP)
phospholipase C mechanism (IP3/Ca++)
steroid hormone mechanism
tyrosine kinase mechanism
guanylate cyclase mechanism (cGMP)
how is arachidonic acid formed?
phospholipase A2 cleaves after inflammatory stimuli
how can a cell have up-regulation for hormone receptors when hormone levels are low?
increase affinity and/or number of receptors
increased synthesis or decreased degradation of receptors
