Term
| What is the Wolff-Chaikoff effect? |
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Definition
| Excess iodine temporarily inhibits thyroid-peroxidase which decreases iodine organification. Results in decreased T3/T4 production. |
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Term
What is the function of TBG (thyroxine binding globulin)?
When does it increase vs. decrease? |
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Definition
Binds most of T3/T4 in blood (so it's not active).
Decreases in hepatic failure.
Increases in pregnancy or OCP use (estrogen increases it) |
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Term
| What converts T4 to T3 and where. |
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Definition
| 5'-deiodinase converts it in peripheral tissues |
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Term
| What is the action of Propylthiouracil? (2) |
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Definition
Inhibits T4-peroxidase (organifies iodine and makes MIT and DIT)
Inhibits 5'-deiodinase to decrease T4 to T3 conversion peripherally |
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Term
| How does Methimazole affect thyroid hormones? |
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Definition
| Inhibits T4-peroxidase (organifies iodine and makes MIT and DIT) |
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Term
| What is the number 1 cause of Cushing's syndrome? |
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Definition
| Exogenous steroids (will see low ACTH) |
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Term
| What causes Cushing's disease? |
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Definition
| ACTH secretion from pituitary adenoma |
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Term
| What labs will you see in adrenal caused Cushing's syndrome? (3) |
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Definition
low ACTH (tumor makes cortisol)
Low and high dose dexamethasone tests both don't change cortisol concentration |
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Term
| What labs will you see in ectopic tumor caused Cushing's syndrome? (3) |
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Definition
high ACTH (tumor makes ACTH)
Low and high dose dexamethasone tests both show no change to cortisol |
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Term
| What labs will you see in Cushing's disease (primary)? (3) |
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Definition
high ACTH
Low dose dexamethasone test, no change to cortisol
High dose dexamethasone test decreases cortisol |
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Term
What are the 2 types of causes of hyperaldosteronism?
What's the difference between the two? |
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Definition
Primary: Adrenal hyperplasia/adenoma (low plasma renin) vs.
Secondary: Kidney perception of low vascular volume (high plasma renin)
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Term
| How to treat hyperaldosteronism |
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Definition
| Spironolactone (a K+ sparing diuretic that works as an aldosterone antagonist) |
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Term
Addison's disease:
- what is it
- 4 labs
- 2 symptoms |
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Definition
- Primary adrenal insufficiency from destruction of cortex
- Low aldosterone and cortisol: cause hyperkalemia (hyponatremia) and acidosis
- skin hyperpigmentation and hypotension |
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Term
| What is secondary adrenal insufficiency and what are its symptoms? |
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Definition
Decreased pituitary ACTH production
no skin hyperpigmentation and no hyperkalemia |
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Term
| What is Waterhouse-Friderichsen syndrome? |
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Definition
| Acute primary adrenal insufficiency due to adrenal hemorrhage from Neisseria meningitidis or cardiogenic shock |
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Term
What is a Pheochromocytoma?
- where, what
- what does it secrete and what is the result |
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Definition
A tumor of the adrenal medulla derived from chromaffin cells (neural crest cells)
Secretes Epi, NE, and dopamine and causes episodic hypertension |
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Term
| What urinary and plasma findings are there in pheochromocytoma? |
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Definition
Urinary: increased VMA (NE breakdown product)
Plasma: increased chatecholamines |
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Term
| 3 syndromes pheochromocytomas are associated with |
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Definition
Neurofibromatosis
MEN 2A
MEN 2B |
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Term
| What do you treat pheochromocytomas with? |
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Definition
| α-antagonists like phenoxybenzamine (a nonselective α-blocker) + surgery |
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