Lecture 61 - Concentration & Osmoregulation Flashcards
Nitrogenous waste is
- urea
- uric acid
urea
deamination of protein produces ammonia that is very toxic to tissues and converted to urea
uric acid
product of nucleic acid breakdown
what enzyme breaks uric acid down
uricase
T/F: when uric acid is broken down it is water-soluble
TRUE
what organ converts NH3 to urea
liver
urea is removed by the ____ and contributes to what
kidneys; interstitial osmotic gradient
ADH ____ urea recycling
increases
what is the ideal plasma osmolality
300 mOsm/L
maintaining plasma osmolality is accomplished by
concentrating or diluting urine
what is required for urine concentration
- formation of medullary osmotic gradient
- presence of ADH/AVP for water reabsorption in collecting duct
how is an osmotic gradient formed
countercurrent multiplier system with juxtamedullary nephrons that create a hyperosmotic medullary interstitium
T/F: shorter loops of juxtamedullary nephrons increase the concentration of filtrate
FALSE - longer
the descending limb of LOH is permeable to ____ and the ascending limb is permeable to ____
water; solutes
T/F: the minimum degree of urine concentration depends on the hypertonicity of the interstitium
FALSE - maximum
what is medullary washout?
- loss of hyperosmotic interstitium in the medulla
- cannot concentrate urine
- patients become polyuric/polydipsic
Antidiuretic hormone (ADH)
- secreted as response to change in volume or osmolality
- causes aquaporins to move to surface of collecting ducts
- results in concentrated urine
what occurs in the absence of ADH
- collecting duct is impermeable to water
- dilute urine
- water loss
urine specific gravity
quantification of urine concentration
iso = .08 - .12
hypo = <.08
hyper = >.12
match the areas of the loop of Henle to the process that occurs there
a. descending limb (thin)
b. thin ascending limb
c. thick ascending limb
- active resorption of water
- active resorption of sodium
- passive resorption of water
- passive resorption of sodium
A = 3
B = 4
C = 2
osmoregulation is mediated by changes where
in water balance
what is the major osmotic molecule
sodium
T/F: changes in plasma Na+ indicate a problem with water balance rather than sodium
TRUE
what 3 mechanisms control osmolality
- ADH/AVP
- thirst
- salt appetite
where are osmoreceptors
hypothalamus
describe a V2-vasopressin receptor
located in collecting ducts and opens aquaporins
describe a V1-vasopressin receptor
located in blood vessels and mediates vasoconstriction
what causes ADH release
- osmolality changes (primary mechanism)
- hemodynamic changes (secondary - volume and pressure)
low osmolality in plasma ____ ADH secretion
inhibits
describe baroreceptors
- located in left atrium, aortic arch, carotid sinus
- senses change in blood volume/pressure
- high blood volume increases stretch and inhibits ADH
diabetes insipidus - central
- inadequate release of ADH from the pituitary
- polyuria and secondary polydipsia
- tx is exogenous
diabetes insipidus - nephrogenic
- collecting ducts do not respond normally to ADH
- defective water channels
how does alcohol impact ADH secretion
- decreases ADH secretion
- polydipsia
- water loss
T/F: small increases in osmolality stimulate thirst
TRUE
what are other triggers of thirst
- change in blood volume/pressure (ECFV depletion, hypovolemia, increased angiotensin II)
- exercise
- stress
what increases salt appetite
decreased [Na+] in ECF or blood volume
where do carnivores get salt? what about herbivores?
carnivores = food sources
herbivores = salt lick
