Flashcards in Adrenal Deck (43)
What are the three zones of the adrenal cortex?
What hormones are made by the zona glomerulosa?
What hormones are made by the zona fasciculata?
What hormones are made by the zona reticularis?
What area is in the center of the adrenal gland?
What hormones are made by the medulla?
What does ACTH actually stimulate within the adrenal gland?
movement of choletserol into mitochondria where the CYP enzymes are located so it can be turned into hormone
What's the classic triad for pheochromocytoma?
What lab tests should be ordered to confirm a diagnosis of pheochromocytoma?
1. 23 hr urine fractionated metanephrines
2. 24 hr urine catecholamines
3. plasma free fractionated metanephrines
(do just urine metanephrines if pre-test probability is low and all three if high)
What are metanephrines and why are they elevated in pheos?
Pheos are catecholamine-secreting tumors that arise from the adrenal medulla.
NE and Epi are metabolized to normetanephrine and metanephrine intratumorally and will then spill into the plasma and are excreted in excess into the urine
Why is the measurement of urine metanephrines preferred over measurement of plasma or urine catecholamines?
Intratumoral metabolism of the catecholamines occurs continuously and independently of catecholamine release, so the levels of metanephrines in the urine will be consistently elevated
catecholamine levels, on the other hand, will vary significantly as release varies; increasing significantly during paroxysms and then returning to normal in between
True or false: metanephrine levels correlate with pheo tumor size.
Why are urine homovanillic acid (HVA) and vanillylmandelic acid (VMA) measured for the diagnosis of neuroblastoma and not metanephrines, since it is also a catecholamine-secreting tumor?
Neuroblastomas originate from sympathetic ganglion cells have contain MAO, but not COMT. This means they produce norepinephrine and dopamine, but no epinephrine
intratumoral inactivation of the NE and dopamine leads to HVA and VMA, not the metanephrines
Why aren't HVA and VMA used for the diagnosis or monitoring of pheochromocytoma?
Dopamine-producing pheos are super rare, so HVA isn't elevated
Pheos have MAO, but much much more COMT, so the VMA level is negligible compared to the VMA from metabolism of sympathetic nerve NE
What enzyme deficiency accounts for over 95% of congenital adrenal hyperplasia cases?
Describe what happens to the hormone levels in 21-hydroxylase deficiency?
There is decreased to no cortisol production, so you get excessive ACTH
this then stimulates the adrenal cortex, but the precursors are shunted to the androgen biosynthetic pathway leading to the accumulation of progesterone and 17-hydroxyprogesterone
What's the clinical presentation of 21 hydroxylase deficiency?
prenatal masculinization (ambiguous genitalia) in females and postnatal virilization in both sexes
What are the clinical and laboratory differences in patients with partial or complete 21-hydroxylase deficiency?
Mild form/partial: the increase in ACTH is able to keep cortisol at normal levels and the 17-OHP in excess causes only a mild salt-wasting with up-regulation of aldosterone in response
the Severe form/complete: low/no aldosterone or cortisol with dehydration due to salt wasting
Very high levels of what precursor are diagnostic for 21 hydroxylase def?
What are the electrolyte abnormalities that can occur in classic congenital adrenal hyperplasia?
(due to the aldosterone deficiency - so this only occurs in complete enzyme loss)
What's considered the gold standard for diagnosing congenital adrenal hyperplasia?
ACTH cosyntropin stimulation test
What is the second most common cause o congenital adrenal hyperplasia and what lab findings would be expected?
11-beta hydroxylase deficiency
elevated 11-deoxycortisol levels
How does 11-beta hydroxylase deficiency differ from 21-beta hydroxylase deficiency clinically?
they both have ambiguous genitalia in females due to androgen excess, but 11-b hydroxylase deficiency also causes hypertension due to 11-deosycortisone's action as a mineralocorticoid
you also get low renin which may result in HYPOkalemia instead of hyperkalemia
What are the common signs and symptoms of hypercortisolism (Cushing's syndrome)?
oligo or amenorrhea
Why do patients with Cushing's syndrome become hypertensive?
cortisol and aldosterone have the same in vitro affinity for the mineralocorticoid receptor, but 11 beta hydroxysteroid dehydrgenase type 2 usually inactivates cortisol to prevent its action at the MR
however, with cortisol excess, this enzyme is overwhelmed, so you get activation of the MR with Na retention and HTN
What three tests are recommended options to screen for Cushing's syndrome?
24-hr urinary cortisol
late night salivary cortisol
overnight low dose dexamethasone suppression test (measure serum cortisol 9 hours later)
What is on the differential diagnosis for Cushing's syndrome?
Cushing's disease (pituitary adenoma)
ectopic ACTH syndrome
Ectopic CRH syndrome
psueo-cushing's syndrome (major depressive disorder or alocoholism)
How is the low-dose dexamethasone test performed and interpreted?
Dex inhibits ACTH production
Low dose (1 mg) is an overnight screening
patients with cushing's syndrome will generally not suppress cortisol (however, some cases of cushing's do suppress, so another test must be used to confirm diagnosis)
What is the high dose dex suppression test and what is it used for clinically?
used to differentiate Cushing's disease from Cushing's syndrome
ACTH secretion in CUshing's disease is only relatively resistant to dex suppression, so in a pituitary adenoma, it will NOT suppress at low dose, but WILL suppress at high dose
(non-pituitary cancer doesn't give a shit and will never suppress)