Physio 10 Flashcards
body balance of water
loses what it gains. gains through ingested food, fluid, and metabolism. loses through urine, feces, sweat, and exhaled air
how do kidneys preserve normal ECF osmolarity?
maximize (concentrate) or minimize (dilute) the osmolarity of the urine in response to changes in ECF osmolarity.
when (U/P)osm = 1, >1, or
1: isotonic.
> 1: hypertonic
osmolar excretion
Uosm X V
typically around 600 mOsm of solute a day in a urine volume of 1.5L. U typically is 400 mOsm/L (600/1.5)
in high water intake, the kidney can make urine osmolarity as low as 30, and in dehydration, as high as 1200 mOsm/L
free water
water not osmotically obligated to remain in the tubular fluid due to the presence of solutes. when the kidney excretes concentrated urine, the free water is taken from the TF and put back into the plasma, and vice versa.
free water clearance formula and definition
Ch2o = V - Cosm
when U/P is 1, Ch2o = 0. kidney neither adds nor removes free water.
when U/P >1, Ch2o
formation of dilute urine
solute (NaCl) reabsorption in the absence of water reabsorption, in tubule segments with low water permeability (thin and thick ascending loop, distal tubule), effectively dilutes the tubular fluid permitting positive free water clearance and excretion of dilute hypo osmotic urine
formation of concentrated urine
Solute reabsorption in the tick ascending limb of the loop of henle generates hypertonic interstitial fluid surrounding the collecting tubules in the renal medulla. osmotic equilibration in collecting duct results in water reabsorption
osmolarity of the tubule fluid along the nephron
tubule fluid is isosmotic in the proximal tubule, hypo osmotic at the end of the loop of henle, and is more dilute or more concentrated at the end of the collecting duct, depending on circulating levels of ADH/AVP
hormonal control of osmolarity through ADH
increases water permeability of the distal nephron segment extending from the cortex to the inner medulla (late distal tubule to the collecting duct). allows absorption of water. 18 minute circulating half life
how does ADH increase water permeability?
inserts aquaporin at the apical membrane allowing flow of water
what is the cellular mechanism of ADH action?
binds V2 receptors in basolateral membrane of principal cells. g protein receptors, make cyclic AMP and activates PKA. synthesizes new aquaporin and fuses vesicles containing aquaporin to the membrane.
what is required for responding to osmolarity changes?
posterior pituitary is necessary
osmoreceptors
located in the organum vasculosum and the subfornical organ of the hypothal. sense plasma osmolarity due to a gap in the blood brain barrier
osmolarity
concentration of osmotically active solutes, moving freely among molecules of water, in a given compartment or designated volume. sum total of all solute concentrations in the given compartment. uses Osmoles as unit (mOsm/L)
