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URINARY > 3. Loop of Henle > Flashcards

3. Loop of Henle Flashcards

1
Q

what is the main function of the proximal tubule

A

major site of reabsorption - 65-75% of all NaCl and H20

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2
Q

what happens to proteins that get through the glomerulus

A

Completely reabsorbed by a Tm carrier mechanism in the proximal tubule

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3
Q

why would some pollutants/drugs not naturally be removed

A

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

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4
Q

how are pollutants/drugs ultimately able to be removed

A

the liver metabolises them to polar compounds - reduces permeability - facilitates their excretion - will stay where kidneys put them

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5
Q

what occurs at the loop of henle

A

reabsorption

NO excretion

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6
Q

what are the components of the loop of henle

A

a descending limb and an ascending limb

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7
Q

what is the osmolarity of the fluid that leaves the proximal tubule

A

300 mOmoles/L = isosmotic to plasma

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8
Q

why is the fluid isosmotic as it laves the proximal tubule

A

because all the solute movement are accompanied by equivalent H20 - i.e. osmotic equilibrium has been maintained

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9
Q

what does the mechanism in the loop of henle allow with regards to urine concentration

A

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

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10
Q

what is the maximum concentration of urine that can be produced by the human kidney

A

1200-1400mOsmoles/l

ie 4x more concentrated than plasma = excess of solute over water

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11
Q

what is the minimum obligatory H20 loss per day

A

500mls

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12
Q

why is there a minimum obligatory H20 loss per day

A

certain substances MUST be excreted each day - urea, sulphate, phosphate, other waste products, non-waste ions (Na+ and K+)

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13
Q

what would happen to the minimum obligatory H20 loss if there was no H2o intake

A

NO CHANGE - as long as kidneys functioning, volume will be excreted even if no H2O intake

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14
Q

what would happen in conditions of excess H2) intake

A

H2O is excreted in excess of solute -

minimum [urine] in man is 30-50 mOsmoles/l ie 10 fold dilution compared with plasma.

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15
Q

what enables the kidneys to produce urine of varying concentration

A

the loops of henle act as COUNTER-CURRENT MULTIPLIERS

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16
Q

what are the permeabilities of the DESCENDING limb of the loop of henle

A

freely permeable to H20

impermeable to NaCl

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17
Q

what are the permeabilities/actions of the ASCENDING limb of the loop of henle

A

actively co-transprot Na+ and Cl- ions out of the tubule lumen

impermeable to H2O - no aquaporins

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18
Q

what does the impermeability to water of the ascending limb mean for osmolarity

A

creates a large osmotic effect

19
Q

if starting with 300mOsm/l of stationary fluid in loop, what is the first thing that occurs to affect osmolarity

A

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

20
Q

what happens to the osmolarity of the tubule as NaCl is removed

A

as concentration decreases - osmolarity decreases

21
Q

what happen to the osmolarity of the interstitium as NaCl is added

A

as concentration increases - osmolarity increases

22
Q

what is the effect on the descending limb of the increased osmotic effect in the interstitium

A

H20 moves out to equate osmolarity

23
Q

what happens to H2O once in the interstitium

A

reabsorbed by the vasa recta (veins following the loop) by the high osmotic pressure and tissue permeability

24
Q

what does this reabsorption of water into the vasa recta enable

A

osmotic gradients to be maintained to further remove NaCl and Water out of their respective parts of the loop

25
Q

fluid is constantly moving through the loop - what is the concentration of the fluid arriving from the descending limb

A

high concentration fluid arrives at the ascending limb - due to water removal at the descending limb

26
Q

what does this high concentration fluid arriving at the ascending limb promote

A

active removal of NaCl

27
Q

what does the active removal of NaCl at the ascending limb promote

A

further concentration of interstitium - increasing osmolarity as body tries to maintain 200mOsm gradient

28
Q

what happens to the fluid concentration as it moves through the tube

A

progressively concentrated as it moves down the descending limb

progressively diluted as it moves up ascending limb

29
Q

what is the overall affect on interstitium concentration as concentrated fluid is delivered to the ascending limb

A

interstitium become more and more concentrated

30
Q

what is the gradient at any horizontal level between the ascending limb and interstitium

A

200mOsmol

31
Q

what does the vertical gradient in the interstitium go from

A

300-1200mOsmol

32
Q

summary of counter current system and osmolarities along the loop - start with fluid at 300 as it exits proximal tubule

A

start with 300

  • starts to concentrate up to 1200 down descending tubule (by removing water)
  • then goes down from 1200 to 100 in ascending tubule (by removing salt)
  • ends up with fluid that contains less salt
33
Q

what happens if the active transport of NaCl out of the ascending limb is stopped e.g. by frusemide

A

all concentration differences are lost and the kidney can only produce isotonic urine:

can’t transport Na out in AL - can’t concentrate interstitium - can’t make osmotic effect to draw water out DL - produces isotonic (300) urine

34
Q

what percentage of the initial filtrate is removed from the loop of henle

A

15-20%

35
Q

what is the osmolarity of the fluid that enters the distal tubule from the loop of henle

A

hypotonic fluid - ie more dilute than plasma

fluid enters loop at 300 and leaves at 100 = hypotonic

36
Q

what are the vasa recta

A

specialised arrangement of peritubular capillaries - veins that follow the loop of henle

37
Q

what is the importance of the vasa recta following the loop

A

means gradient is maintained as water is reabsorbed by veins as it goes along

38
Q

how do the vasa recta maintain/mediate the interstitial gradient

A

are freely permeable to both H20 and solutes - equilibrate at any given level with osmolarities

39
Q

what moves in and out if the vasa recta at the DL

A

Na in

H2O out

40
Q

what moves in and out of the vasa recta at the AL

A

H20 in

Na out

41
Q

what are the 3 main functions of the vas recta

A
  1. provide O2 for the medulla
  2. does not disturb/maintains gradient
  3. removes volume from the interstitium
42
Q

why is the flow rate through the vasa recta very low

A

to allow plenty of time for equilibration to occur with the interstitium

43
Q

what is the site of water regulation in the nephron and what regulates it

A

the collection duct - regulated by ADH (vasopressin)

more ADH = less fluid lost

URINARY (27 decks)

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