L19: Urine Concentration & Dilution Flashcards
what is the maximum urine concentration that the kidneys can produce?
1200-1400
normal 600 per 0.5 L/day
what is required by kidney tubules for formation of concentrated urine?
- -ADH
- -high osmolarity
what is the obligatory volume of excreted urine per day?
0.5 L/day
where in the kidney tubules are most of the filtered electrolytes reabsorbed?
65% in proximal tubule
compare permeability to water in the proximal tubule, descending, thin and thick ascending loops of henle
p - highly permeable
des - highly permeable
thin/thick - impermeable
countercurrent mechanism
using energy to conc. urine as if flows thru the nephrons in kidneys
ascending thick limb of henle and distal cortical collecting tubule are impermeable to
water and urea
increase in ADH in cortical collecting tubule
normally impermeable to water and urea
now permeable to water but not permeable to urea
resulting in a higher concentrated urine
explain how a high conc. of urea can be maintained in the collecting tubules even as it is being reabsorbed
thru the simultaneous mvt of water and urea out of tubules
this keeps the urea conc. high
only 20-25% of urea is urinated
what is the role of osmoreceptor-ADH feedback mechanism
control extracell fluid Na conc. and osmolarity
increased conc. fluid osmolarity results in the shrinking of
osmoreceptor cells in anterior hypothalamus
resulting in action potentials
causing the release of ADH
ADH increases permeability to water in the
distal nephron segments
where is ADH formed
magnocellular neurons in the hypothalamus
supraoptic and paraventricular nuclei
where is ADH stored
stored and secreted by the posterior pituitary
what is the function of osmoreceptor cells
associated w/ causing action potentials causing the release of ADH
