3. Loop of Henle Flashcards
what is the main function of the proximal tubule
major site of reabsorption - 65-75% of all NaCl and H20
what happens to proteins that get through the glomerulus
Completely reabsorbed by a Tm carrier mechanism in the proximal tubule
why would some pollutants/drugs not naturally be removed
lipid soluble - would just pass through lipid membrane - could never be removed
removal of H20 in the proximal tubule would establish concentration gradients for their reabsorption
how are pollutants/drugs ultimately able to be removed
the liver metabolises them to polar compounds - reduces permeability - facilitates their excretion - will stay where kidneys put them
what occurs at the loop of henle
reabsorption
NO excretion
what are the components of the loop of henle
a descending limb and an ascending limb
what is the osmolarity of the fluid that leaves the proximal tubule
300 mOmoles/L = isosmotic to plasma
why is the fluid isosmotic as it laves the proximal tubule
because all the solute movement are accompanied by equivalent H20 - i.e. osmotic equilibrium has been maintained
what does the mechanism in the loop of henle allow with regards to urine concentration
enables kidney to produce concentrated urine in times of H20 deficit - i.e. can reabsorb more water to protect the body - excreting less water per molecule of substance excreted
what is the maximum concentration of urine that can be produced by the human kidney
1200-1400mOsmoles/l
ie 4x more concentrated than plasma = excess of solute over water
what is the minimum obligatory H20 loss per day
500mls
why is there a minimum obligatory H20 loss per day
certain substances MUST be excreted each day - urea, sulphate, phosphate, other waste products, non-waste ions (Na+ and K+)
what would happen to the minimum obligatory H20 loss if there was no H2o intake
NO CHANGE - as long as kidneys functioning, volume will be excreted even if no H2O intake
what would happen in conditions of excess H2) intake
H2O is excreted in excess of solute -
minimum [urine] in man is 30-50 mOsmoles/l ie 10 fold dilution compared with plasma.
what enables the kidneys to produce urine of varying concentration
the loops of henle act as COUNTER-CURRENT MULTIPLIERS
what are the permeabilities of the DESCENDING limb of the loop of henle
freely permeable to H20
impermeable to NaCl
what are the permeabilities/actions of the ASCENDING limb of the loop of henle
actively co-transprot Na+ and Cl- ions out of the tubule lumen
impermeable to H2O - no aquaporins
what does the impermeability to water of the ascending limb mean for osmolarity
creates a large osmotic effect
if starting with 300mOsm/l of stationary fluid in loop, what is the first thing that occurs to affect osmolarity
NaCl actively pumped out of the ascending limb - causes concentration to fall in tubule - concentration in interstitium rises - occurs until limiting gradient of 200mOsm is established
what happens to the osmolarity of the tubule as NaCl is removed
as concentration decreases - osmolarity decreases
what happen to the osmolarity of the interstitium as NaCl is added
as concentration increases - osmolarity increases
what is the effect on the descending limb of the increased osmotic effect in the interstitium
H20 moves out to equate osmolarity
what happens to H2O once in the interstitium
reabsorbed by the vasa recta (veins following the loop) by the high osmotic pressure and tissue permeability
what does this reabsorption of water into the vasa recta enable
osmotic gradients to be maintained to further remove NaCl and Water out of their respective parts of the loop
