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31 Cards in this Set
- Front
- Back
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How is Thyroid hormone (T3/T4) production stimulated?
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By TSH from the pituitary
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What stimulates the pituitary to release TSH?
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TRH form the hypothalamus
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How could you test for pituitary TSH secretory function? Would you?
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With a TRH-stimulation test, but no this is not done anymore.
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What is Thyrotropin-alpha?
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Recombinant TSH
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What is recombinant TSH used for?
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Evaluating for Thyroid cancer
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How do you evaluate for Thyroid cancer?
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1. Give radio-labeled iodine, then recomb TSH
2. Measure the degree of radionucleotide iodine uptake and thyroglobulin production |
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What else can you diagnose by looking for uptake of the radio labelled iodine in response to TSH injection?
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Metastasis - iodine uptake at other sites in the body
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What is the great thing about being able to give recombinant TSH to test for recurrent or metastatic Thyroid cancer?
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Patients dont have to go off their levothyroxine for 4-6 weeks in order to release TSH from neg fb; just give it exogenously!
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What are the 2 major parameters that will modify Vasopressin/ADH secretion to restore the parameters to normal values?
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-Blood volume
-Osmolality |
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So what detects increased blood osmolality (Na conc)?
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Osmoreceptors in the brain
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What happens when osmoreceptors detect increased blood osmolality?
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They stimulate the posterior pituitary to release vasopressin/ADH
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What effect does ADH have?
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Increases concentration of aquaporins in the distal tubule and collecting duct of the kidney to increase H2O reabspn
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What effect does water retention have?
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It decreases blood osmolality (Na conc) back to normal.
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Is ADH secretion the only thing stimulated by osmoreceptor detection of increased osmolarity?
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No, thirst is also stimulated!
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So the 2 things that will stimulate ADH release are:
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-Decreased blood vol
-Increased serum osmolality |
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Which is the more important day-to-day controller of ADH release?
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Blood osmolality
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What is the disease in which Vasopressin is deficient?
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Central/Pituitary Diabetes insipidus
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What is the disease in which the kidney is insensitive to Vasopressin, though ADH is present?
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Nephrogenic Diabetes insipidus
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What are the 2 main symptoms of Diabetes insipidus?
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Polyuria (pee insipid amts)
Hypotonic urine (clear pee) |
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What is Primary Polydipsia?
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A psychiatric disease of excessive water intake
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What test is done to differentiate Central vs Nephrogenic DI and Primary polydipsia?
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The water deprivation test
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What happens in a NORMAL individual when they are water deprived?
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-Plasma osmolality goes up due to lack of volume
-Urine osmolality goes up massively |
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What happens to a person with complete nephrogenic DI when you deprive them of water?
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Plasma osmolality skyrockets
Urine osmolality does nothing - they continue to pee insipid amts of hypotonic urine because they have no response to ADH |
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What are baseline plasma levels of ADH like in patients with nephrogenic DI? Why?
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Elevated - the brain thinks it needs to keep kicking more ADH out even tho the kidneys dont respond to it.
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What are baseline plasma levels of ADH like in patients with CENTRAL pituitary DI?
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Absent; that's why its called central diabetes insipidus.
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When you inject DDAVP (vasopressin) what will be the response in a patient with
-Complete nephrogenic DI -Complete central DI |
Complete nephrogenic: there will be no response at all
Complete central DI: there will be a blip of increased urine osmolality |
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Why won't massive amounts of ADH result in increased urine osmolality all the way to normal in patients with complete central diabetes insipidus?
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Because after the years of peeing out hypotonic urine they have washed out their renal medullary gradients and cannot concentrate urine above ~300 mOsm
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How does water deprivation in patients with PARTIAL nephrogenic or central DI compare to the ones with complete?
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They will START to increase urine osmolality, but not enough to reduce plasma osmolality back down to normal.
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And how can you differentiate partial central DI from partial nephrogenic?
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Only central DI will respond to DDAVP challenge.
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What does Primary polydipsia look like in a water deprivation test and DDAVP challenge?
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Just like Partial Nephrogenic DI
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Why won't a patient with Primary Polydipsia respond to DDAVP?
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Nothing is wrong with their ADH! Adding more won't do anything for them.
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