loop of henle

Question 1

important feature of the fluid that leaves the proximal tubule

Answer 1

fluid that leaves the proximal tubule is isosmotic with plasma ie 300mOmoles/l

Question 2

why is fluid that leaves proximal tubule isosmotic with plasma

Answer 2

because all solute movements are accompanied by equivalent H20 movements, so osmotic equilibrium is maintained

Question 3

what does loop of henle mechanism allow

Answer 3

kidney to produce concentrated urine in times of H20 deficit, a major determinant of out ability to survive without water

Question 4

maximum concentration of urine that can be produced

Answer 4

1200-1400mOsmoles/l

i.e. 4x more concentrated than plasma
excess solute over water

Question 5

what is the minimum obligatory H20 loss

Answer 5

500mls

Question 6

why is there a minimum obligatory H20 loss

Answer 6

urea, sulphate, phosphate and other waste products and non-waste ions (Na and K) must be excreted each day in amount to ~600mOsmoles - obligatory water loss

Question 7

what happens when excess H20 intake

Answer 7

H20 is excreted in excess of solute

Question 8

minimum urine concentration

Answer 8

30-50mOsmoles/L

10 fold dilution compared w plasma

Question 9

how are kidneys able to produce urine of varying concentration

Answer 9

because the Loops of Henle of juxtamedullary nephrons act as counter-current multipliers

Question 10

what are critical characterisics of Loop of Henle which make it counter-current multipliers

Answer 10

1. ascending limb actively transports Na+ and Cl- ions out of the tubule lumen into interstium. the ascending limb is impermeable to H20
2. descending limb is freely permeable to H20 but relatively impermeable to NaCl

Question 11

why does fluid become progressively concentrated as move down descending limb

Answer 11

removal of water

Question 12

why does fluid become more diluted as move up ascending limb

Answer 12

removal salt

Question 13

what is the key step

Answer 13

active transport of NaCl out of ascending limb

Question 14

what does counter-current multiplier acheive

Answer 14

1. concentrates fluid on way down and re-dilutes on way back up (not by adding H2O but by removing NaCl)
2. 15-20% initial filtrate is removed from loop of henle
3. fluid which enters distal tubule is more dilute than plasma

Question 15

what is significance of counter-current multiplier

Answer 15

it creates an increasingly concentrated gradient in the interstitium

also delivers hypotonic fluid to distal tubule

Question 16

vasa recta

Answer 16

specialised arrangement of peritubular capillaries of juxtaglomerular nephrons also participating in countercurrent mechanism by acting as countecurrent exchangers

Question 17

how are vasa recta arranged

Answer 17

as hairpin loops and therefore do not carry away NaCl removed from loop of henle and so do not interfee with the gradient

Question 18

functions of vasa recta

Answer 18

1. provide O2 for medulla
2. in providing O2 must not disturb gradient
3. removes volume from interstitium

Question 19

starlings forces in vasa recta

Answer 19

in favour of reabsorption due to high oncotic pressure and high tissue pressure due to tight renal capsule which drives fluid into capillaries

Question 20

flow rate through vasa recta

Answer 20

very low so there is plenty of time for equilibrilation o oxxur within interstitum,

Question 21

site of water regulation

Answer 21

collecting duct

Question 22

what controls collecting duct permeability to water

Answer 22

anti-diuretic hormone

Question 23

what does ADH do

Answer 23

determines whether or not the dilute urine delivered to the distal tubule is concentrated and to what extent