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85 Cards in this Set
- Front
- Back
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most common cause of HYPERthyroidism
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Graves' Disease
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Graves' Disease
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autoimmune disease - Ig against thyroid gland
thyroid stimulating Ig (TSI) bind to TSH receptors on thyroid, simulating the effects of TSH --> goiter |
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What happens with TSH and TRH in Graves' Disease?
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Excess thyroid hormones --> neg feedback on pituitary, suppressing TSH secretion
pituitary unresponsive to TRH stimulation |
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Ophthamologic correlation to Graves' Disease
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autoimmune attack against eye muscles and orbital CT --> EXOPHTHALMOS (protrusion of the eyes)
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Drug that blocks thyroid hormone synthesis
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PTU
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Drugs that relieve hyperthyroid symptoms
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beta-blockers (b/c most symptoms caused by enhanced SNS activity)
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2 ways to remove parts of thyroid in cases of hyperthyroidism
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radioactive iodide - taken up by thyroid - kills cells
surgery |
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3 types of goiter
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goitrous hypothyroidism
euthyroid goiter goiter associated with hyperthyroidism |
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What does the hypothalamus secrete to stimulate corticotroph cells in the pituitary?
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corticotropin-releasing hormone (CRH)
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What conversion does ACTH mediate in the adrenal cortex?
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conversion of cholesterol to pregnenolone
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first step in steroid hormone synthesis
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conversion of cholesterol to pregnenolone
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Three hormones synthesized upon ACTH stimulation of the adrenal cortex.
1 --> neg fdbk 2 don't |
cortisol - suppresses CRH secretion in the hypothalamus & ACTH secretion in the pituitary
adlosterone androgens |
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what is POMC (pro-opiomelanocortin)?
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large protein synthesized by corticotropes and pars intermedialis cells
cleaved into ACTH and other hormones |
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Stimulators of ACTH secretion (3)
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cortisol decrease
sleep-wake transition stress |
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Inhibitor of ACTH secretion
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cortisol increase
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Describe circadian trend in CRH and ACTH secretion
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most frequent bursts in early morning (during sleep, just before awakening)
least frequent in evening |
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Dexamethasone
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synthetic glucocorticoid 30x more potent than cortisol
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Effects of dexamethasone
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Negative feedback inhibition of CRH & ACTH secretion
--> sharp decline in adrenal cortisol release --> drop in plasma cortisol --> decrease in urinary exretion of cortisol metabolites |
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What is dexamethasone suppression test used for?
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determining if hypothalamic-pituitary-adrenal axis responds normally
(cortisol concentration should drop) |
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Addison's disease
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primary adrenal insufficiency
gradual autoimmune destruction of entire adrenal cortex |
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secondary adrenal insufficiency
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caused by ACTH deficiency
deficiency of cortisol and adrenal adrogens renin-angiotensin system would maintain aldosterone synthesis in the zone glomerulosa |
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most common cause of secondary adrenal insufficiency
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physician-induced (iatrogenic)
suppression of hypothalamic CRH & ACTH secretion after stopping exogenous high-dose glucocorticoid tx |
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Two ways to test adrenal cortex function
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ACTH stimulation of cortisol secretion
Insulin-induced hypoglycemia to stimulate cortisol secretion |
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Effects of long term glucocorticoid tx
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CRH-ACTH suppressed (neg fdbk)
adrenal atrophy, less responsive to ACTH suppression of CRH and ACTH |
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Why is it bad to abruptly end long-term glucocorticoid tx?
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Adrenal cortex insenstive to ACTH. Unable to respond appropriately to hypothalamic-pituitary-adrenal axis signals.
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Common precursor of steroid hormone
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cholesterol
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21 carbon steroid hormones
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glucocorticoids (cortisol)
mineralcorticoids (aldosterone) progesterone |
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19 carbon steroid hormones
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androgens (testosterone, DHEA, DHEA-S)
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18 carbon steroid hormones
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estrogens (estradiol)
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25 carbon steroid hormones
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calciferols (vit. D)
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2 major adrenogenic products of the adrenal gland
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DHEA & DHEA-S
(testosterone precursors) |
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During puberty, DHEA & DHEAS are primarily responsible for _____
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development of pubic/axillary hair (andrenarche)
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Metyrapone
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inhibits last step in cortisol biosynthesis, causing acute cortisol deficiency
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Describe metyrapone test
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increase in 11-deoxycortisol (immed. precursor to cortisol) demonstrates hypothal-pit-adrenal axis is working normally
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3 urinary steroids and metabolites
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17-OHCs
17-KS urinary free cortisol |
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How should urine be collected to measure urinary cortisol?
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over 24 hours because of circadian variation
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steroid hormones regulate the transcriptions of specific genes via...
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steroid hormone regulatory elements (HRE) on DNA in target cells
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Net metabolic actions of cortisol - anabolic/catabolic?
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catabolic
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How is cortisol PERMISSIVE?
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not directly initiate certain processes, but allows them to occur efficiently when these processes are stimulated by other hormones
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Most important overall action of cortisol
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facilitate conversion of protein to glycogen
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benefit of cortisol's catabolic and anti-anabolic effects
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prevents hypoglycemia during fasting
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detriment of excess cortisol
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continuous drain on body stores than cannot be compensated with dietary protein, b/c excess cortisol inhibits protein synthesis
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What PERMITS increased amino acid mobilization and GNG to occur during fasting?
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Previous exposure to normal cortisol concentrations
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Excess _____ (what hormone?) promotes insulin resisitance
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cortisol
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What is the benefit of cortisol-mediated insulin resistance
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During fasting, diverts glucose away from muscle/adipose cells and toward the brain
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Secretion of aldosterone is regulated by the _____ loop
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renin-angiotensin system feedback loop
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Which cells secrete renin?
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juxtaglomerular cells of the kidney
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Renin acts on what substrate in the bloodstream?
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angiotensinogen
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Where is angiotensin I cleaved and by what?
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Angiotensin I is cleaved by ACE in the lung vasculature to create angiotensin II
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Function of angiotensin II
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potent vasoconstrictor: raises BP
gradually damages heart and kidneys stimulate aldosterone synthesis & secretion by stimulating first step of aldosterone synth in the zona glomerulosa |
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Function of aldosterone
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increases renal sodium reabsorption
-->: increase ECF volume & increase BP |
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Increased aldosterone _____ renin secretion
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DECREASES
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Relationship btw aldosterone and plasma K+
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When K+ stimulates zona glomerulosa,
aldosterone increases renal K+ exretion, lowerling plasma K+ |
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Function of ACE inhibitors
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control BP
decrease formation of angiotensin II tx HTN, CHF, renal ds |
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relevant hormone levels for pt's on ACE inhibitors
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decreased angiotensin II -->
decreased aldosterone --> increased circulating renin --> increased angiotensin I |
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3 things that activate renin secretion
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juxtaglomerular cells of the kidney (baroreceptors)
macula densa cells (Na+ -sensitive chemoreceptors) sympathetic nerves innervating the kidney |
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What hormone accounts for most mineralcorticoid activity?
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aldosterone
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aldosterone precursor
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DOC
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primary target organ of aldosterone
-target cells |
kidney: tubule cells of distal nephron
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What does aldosterone promote in the tubule cells of the distal nephron?
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sodium reabsorption in exchange for K+ or H+ ions, which are lost in urine
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Sodium retention leads to (3 things):
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increase in ECF volume
increase in intravascular volume increase in BP |
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Mineralcorticoids exaggerate aldosterone effects leading to (3 things):
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HTN
hypokalemia (low plasma K+) alkalosis |
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Anything that __________ will increase aldosterone secretion via the renin-angiotensin system.
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Anything that REDUCES TOTAL BODY SODIUM AND/OR ECF VOLUME will increase aldosterone secretion via the renin-angiotensin system.
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Adrenal medulla is innervated by ____
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cholinergic preganglionic fibers from teh greater splanchnic nerve
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Chromaffin cell
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normal adrenal medullary cell
store epi; released upon ACh stimulation |
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basal plasma epi levels
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25-50 pg/mL
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Net metabolic effect of epinephrine
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rise in plasma glucose, FFA and ketoacids
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phreochromocytomas
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tumors of chromaffin cells, which secrete excess catecholamines --> HTN
part of multiple endocrine neoplasia (MEN) |
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Normal range for plasma calcium
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8.5-10.5 mg/dl
(50% ionized/biologically active) |
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A rise in plasma phosphate causes a _____ in plasma calcium
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decrease
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Phosphate is found mostly in the ____ in association with _____
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Phosphate is found mostly in the SKELETON in association with CALCIUM
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Phosphate excretion is enhanced by what hormone?
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PTH
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PTH is excreted in response to
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low calcium
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PTH binds to what type of receptor?
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G-protein coupled
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Major target tissues of PTH
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bone
kidney |
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What vitamin metabolite does PTH work with?
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1, 25 (OH) vitamin D
release of calcium & phosphate from bone |
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Sustained levels of PTH result in...
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low phosphate (from increased excretion)
high calcium |
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Tx for hypercalcemia
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hydration and sodium intake - increases calcium excretion
Calcitonin |
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net effect of vitamin D
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increase plasma calcium and phosphate levels
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calcitonin is secreted in response to...
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increased ionized calcium concentration
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effects of chronic magnesium deficiency
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suppress PTH secretion, leading to hypocalcemia
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2 causes of hypercalcemia
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excess PTH
excess vitamin D |
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symptoms of hypercalcemia
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polyuria, polydipsia
kidney stones CaPO4 xstals in kidneys |
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2 causes of hypocalcemia
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PTH deficiency
vitamin D deficiency |
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tx of hypocalcemia
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calcium + vitamin D
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