Exam - Urine Formation Flashcards
how does the kidney regulate water balance
dilutes or concentrated urine in accordance with hydration state
how does water movement occur
by osmosis through p ores
what does the dilution/concentration of urine depend on
the osmolarity of interstitial and tubular fluids in the kidney
what increases osmolarity from the medulla to the pelvis in kidneys
handling of ions, urea and water - allows urine to be secreted at a higher osmolarity than plasma
what are the 3 components
hypertonic medullary interstitium
dilution of the tubule fluid in the thick ascending limb and distal convoluted tubule
variability in water permaibilty of collecting duct in response to vasopressin
what does hypertonic medullary intersitium allow
concentrated urine
what does the dilution of the tubule fluid in the thick ascending limb and the distal convoluted tubule allow for
diluted urine
what is the counter-current multiplier
the loop of Henle has 2 parallel limbs that run in opposite directions
what are the 2 limbs in the loop of henle
descending (cortex –> medulla)
ascending (medulla –> cortex)
what do epithelial cells in the ascending limb of the loops of henle do
actively pump Na+ accompanied by secondary transport of K+ and Cl-
what is the ion ratio in the ascending limb
1 Na+
1 K+
2 Cl-
characteristic of the epithelial cells in the ascending limb
apical membrane is impermeable to water
characteristic of epithelial cells in the descending l limb
no active pumps, highly permeable to water
where does tubular fluid pass through distal tubule/collecting duct
from cortex to medulla = increase in interstitial osmolarity
when will water be allowed to exit the duct through epithelial cells
only if ADH is present
what does ADH stimulate
formation of aquaproins on the apical membrane of epithelial cells
what happens when ADH decreases
number of aquaporins decreases and water is not reabsorbed
where is ADH produced
hypothalamus
where is ADH stored
posterior pituitaru
what sense plasma osmotic pressure
hypothalamic osmoreceptors
what does an increase in osmolarity do
increase stimulus for ADH release
what does an increase in ADH release do
acts via cAMP/protein kinase to insert aquaporins in distal tubules and collecting ducts
what do hypothalamic osmoreceptors send
excitatory signals to thirst centres in the hypothalamus
what does urea participate in
maintaining the high interstitial osmolarity in the medulla
what does urea account for
approx 40% of the osmolarity of the medullary interistitum
how does urea recirculate
collecting duct epithelium is moderately permeable to urea –> moves into intersituium–> re-enters ascending limb of loop of henle
what does the recirculation of urea help ensure
that the required amount of urea is excreted even if urine volume is low
what do the capillaries of the vasa recta make
hairpin bends similar to the loop of Henle
what does the osmolarity in the capillaries follow
the medulla gradient
what is the result of the vasa recta
ions and urea responsible for the gradient along the loop of Henle remain in the interstitial fluid - if mot, no osmotic gradient would occur
what percentage of body mass is water
60-70%
where is half the water present
in cells
where is the rest of water present
interstitial fluid
blood plasma
lymphs
where is movement of water easy
between compartment
what is water movement driven by
hydrostatic pressure
osmotic presseure
