Loop of Henle

Question 1

What is the function of the proximal tubule?

Answer 1

Reabsorption
65-75% NaCl
H2O
Nutritionally Important substances

Question 2

How much albumin is secreted a day? What happens to it?

Answer 2

30g/0.5%

Completely reabsorbed

Question 3

How are lipid soluble pollutants removed from the system?

Answer 3

Liver metabolises them into polar compounds - reduces permeability

Question 4

What is the normal osmolarity of fluid leaving the proximal tubule?

Answer 4

Isosmotic - 300mOmoles/l

Question 5

Why is fluid leaving the proximal tubule isosmotic?

Answer 5

Solute movements are accompanied by H2O movements

Question 6

The proximal and distal tubules sit where?

Answer 6

The cortex

Question 7

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

Answer 7

1200-1400mOsmoles/l

Question 8

Why does the human kidney have a minimum obligatory H2O loss? What is it?

Answer 8

500mls

Because there are waste products amounting to 600mOsmoles which must be excreted

Question 9

What is the minimum [urine] in a human?

Answer 9

30-50mOsmoles

Question 10

The loops of Henle act as what?

Answer 10

Counter-current multipliers

Question 11

What is meant by counter current?

Answer 11

Fluid flows down descending limb, up ascending limb

Question 12

What is meant by a (counter-current) multiplier?

Answer 12

Ascending limb actively contransports NaCl out, whilst impermeable to H2O
Descending limb freely permeable to H2O, impermeable to NaCl

Question 13

What is the limiting gradient osmolarity in the ascending limb of the loop of Henle?

Answer 13

200mOsm

Question 14

What is the net effect of removing NaCl from the ascending limb into the interstitium?

Answer 14

Osmolarity of the lumen decreases

Osmolarity of the interstitium increases

Question 15

The increased osmolarity in the interstitium next to the ascending limb causes what?

Answer 15

H2O outflow from ascending limb to counteract osmolarity

Question 16

Why does H2O outflow from the descending limb not cause isosmolarity in the adjacent interstitium?

Answer 16

This water is reabsorbed by the high oncotic and tissue pressure into the vasa recta

Question 17

Greater concentration of the descending limb causes what?

Answer 17

Greater concentration of the interstitium by adding salt from ascending limb

Question 18

What is the vertical gradient of the interstitum?

Answer 18

300–>1200 mOsmol

Question 19

How do Loop diuretics effect diuresis?

Answer 19

Block active transport of NaCl out of ascending limb - no conc differences - no gradient in the medulla
Only isotonic urine

Question 20

What is the key step which causes a concentration gradient in the medulla?

Answer 20

Active transport of NaCl

Question 21

What does the countercurrent multiplier achieve?

Answer 21

1. Dilutes by removing NaCl
2. 15-20% of intial filtrate removed from loop of henle
3. Fluid in tubule more dilute than plasma (hypotonic)

Question 22

What are the vasa recta?

Answer 22

Arrangement of peritubular capillaries of the juxtamedullary nephrons that participate in the countercurrent mechanism

Question 23

Why do the vasa recta not drain NaCl in the Loop interstitium?

Answer 23

Hairpin loop arrangement to not interfere with the gradient

Question 24

What are the functions of the vasa recta?

Answer 24

• Provide medulla O2
• NOT disturb the gradient
• Remove volume from interstitium

Question 25

How much volume is removed from the interstitium by the vasa recta?

Answer 25

Up to 36l/day

Question 26

What is the flow rate of the vasa recta?

Answer 26

Very low

Question 27

Why is the flow rate of the vasa recta so low?

Answer 27

To give time for the equilibrium with the interstitium to take place

Question 28

Why are the starling forces in the vasa recta in favour of reabsorption?

Answer 28

High oncotic pressure and high pressure

Question 29

Permeability of the collecting duct to water is dependent on what?

Answer 29

ADH (vasopressin)

Question 30

ADH is secreted by what?

Answer 30

Posterior pituitary

Question 31

What is the role of ADH?

Answer 31

Control concentration of urine in the collecting duct