Loop of Henle

Question 1

What is the function of the proximal tubule?

Answer 1

Major site of reabsorption
65-75% of NaCl and H2O

Question 2

How much protein (particularly albumin) gets though tubule?

Answer 2

20g/day so 0.5% of total amount presented at glomerulus
Completely reabsorbed by a Tm carrier mechanism in proximal tubule

Question 3

Describe drugs and pollutants and tubular function

Answer 3

Many are non polar and high lipid soluble so removal of H2O in proximal tubule establishes conc. gradients for their reabsorption
Liver metabolises them polar so reduces their permeability and facilitates the excretion

Question 4

What is the fluid described as when it leaves the proximal tubule?

Answer 4

Isosmotic with plasma - 300mOmoles/l

Question 5

Why is the fluid leaving the proximal tubule isosmotic with plasma?

Answer 5

All solute movements are accompanied by equivalent H2O movements so osmotic equilibrium is maintained

Question 6

What process is attributable to the loops of Henle of juxtamedullary nephrons?

Answer 6

Essential for water balance

Question 7

Where are the nephrons distal and proximal tubules?

Answer 7

In cortex
All nephrons have common processes for reabsorption and secretion of solutes of filtrate

Question 8

What does the mechanism of the loop of Henle ensure?

Answer 8

The kidney can produce concentrated urine in times of H2O deficit

Question 9

What is the max. conc. of urine that can be produced by the human kidney?

Answer 9

1200-1400mOsmoles/l so 4 x more concentrated than plasma as excess of solute over water

Question 10

What is the minimum obligatory H2O loss and why?

Answer 10

500mls
As this is required to excrete 600mOsmoles of waste products (urea, sulphate and phosphate) and non-waste ions which must be excreted

Question 11

What happens if no H2O intake?

Answer 11

Functioning kidneys still excrete 500mls so urinate to death

Question 12

What is the min. conc. of urine?

Answer 12

30-50mOsmoles/l so 10 fold dilution compared with plasma
In conditions of excess H2O

Question 13

How are kidneys able to produce urine of varying conc.?

Answer 13

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

Question 14

What is counter current?

Answer 14

Fluid flows down descending limb and up the ascending limb

Question 15

What are the critical characteristics that make loops counter-current multipliers?

Answer 15

Ascending limb actively co-transports Na and Cl ions out of tubule lumen into interstitium
Ascending limb impermeable to H2O
Descending limb is freely permeable to H2O but relatively impermeable to NaCl

Question 16

What happens after loop of Henle is filled with stationary isosmotic fluid (300mOsmoles/l)?

Answer 16

Active removal of NaCl from ascending limb - is put into interstitium so osmolarity in tubule decreases and increases in interstitium

Question 17

What happens when the descending limb is exposed to greater osmolarity in interstitium?

Answer 17

H2O will move out to equate the osmolarity
H2O does not stay in the interstitium but is reabsorbed by high osmotic and tissue pressure into vasa recta

Question 18

What happens when fluid is moving in the loop of Henle?

Answer 18

Fluid is entering at proximal and leaving at distal
Concentrated fluid in descending limb rounds the bend and delivers a high conc. to ascending limb - active NaCl removal which further concentrates the interstitium

Question 19

What does greater conc. of descending (by removal of water) limb mean?

Answer 19

Greater conc. of interstitium by addition of salt from ascending limb

Question 20

Where in the tubule is the conc. of fluid more and progressively diluted?

Answer 20

More concentrated - as moves down descending limb
Diluted - moves up ascending limb

Question 21

At horizontal level what is the mOsmol gradient between ascending limb and interstitium?

Answer 21

200mOsmol
As 100 in ascending and 300 in interstitium

Question 22

What happens when more and more concentrated fluid is delivered to ascending limb?

Answer 22

The interstitium becomes more and more concentrated

Question 23

What is the vertical gradient in the interstitium?

Answer 23

300 to 1200mOsmol

Question 24

What is the key step in the loop of Henle?

Answer 24

Active transport of NaCl out of ascending limb
If abolished then (ex. by use of diuretic frusemide) all conc. differences are lost and kidney produces isotonic urine

Question 25

What has the counter-current multiplier achieved?

Answer 25

Concentrates fluid on way down and dilutes on way up, by removing NaCl
Consequence - 15-20% of initial filtrate is removed from loop of Henle
Fluid which enters tubule is more dilute than plasma

Question 26

What is the significance of the counter-current multiplier?

Answer 26

Creates an increasingly concentrated gradient in the interstitium

Question 27

What does the counter-current multiplier deliver to the distal tubule?

Answer 27

hypotonic fluid

Question 28

What is the main importance of the counter-current multiplier?

Answer 28

All about concentrating the medullary interstitium
And delivering hypotonic fluid to the distal tubule

Question 29

What is the vasa recta?

Answer 29

Specialized arrangement of peritubular capillaries of juxtamedullary nephrons

Question 30

How does the vasa recta participate in the counter-current mechanism?

Answer 30

By acting as counter-current exchanges
They are arranged as hairpin loops and therefore don’t interfere with gradient
Vasa recta are freely permeable to H2O and solutes so equilibrate the medullary interstitial gradient

Question 31

What are the functions of the vasa recta?

Answer 31

Provide O2 for medulla
In providing O2 must not disrupt gradient
Removes volume from interstitium - up to 36l/day

Question 32

How are the Starling’s forces in favour of reabsorption in vasa recta?

Answer 32

High osmotic pressure and high tissue pressure due to tight renal capsule which drives fluid into capillaries

Question 33

What is the flow rate of vasa recta?

Answer 33

Very low so there is plenty of time for equilibration to occur with interstitium and does not disturb medullary gradient

Question 34

Where is the site of water regulation?

Answer 34

Collecting duct - whose permeability is under control of ADH

Question 35

What does the presence of ADH determine?

Answer 35

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