Lecture 5 - Loop of Henle

Question 1

What part of the tubule is the primary site of reabsorption?

Answer 1

Proximal tubule

Question 2

Is any protein filtered?

Answer 2

Some protein does get through, esp. albumin but this is completely reabsorbed via Tm carrier mechanisms in the PCT

Question 3

Why does the liver make a lot of drugs and pollutants that are non-polar polar?

Answer 3

Nonpolar substances can be easily reabsorbed but polar compounds have decreased permeability and hence are excreted more

Question 4

What is the collecting duct of the tubule responsible for?

Answer 4

Water regulation under the influence of ADH

Question 5

What is the loop of henle of the tubule responsible for?

Answer 5

Reabsorption only

NO secretion

Question 6

What are the two ‘limbs’ of the loop of Henle?

Answer 6

Ascending and descending

Question 7

Describe what the fluid leaving the PCT is like?

Answer 7

Isotonic with plasma (this is because all the solute movements are accompanied by equivalent H2O movements)

Question 8

Through what mechanism is the kidney able to produce concentrated urine in times of H2O deficit?

Answer 8

Loop of henle juxtamedullary nephrons

Question 9

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

Answer 9

1200-1400mOsmoles/L

x4 more concentrated than plasma

Question 10

Why is their an obligatory minimum loss of 500mls of water per day?

Answer 10

Urea, sulphate, phosphate, ammonia and other waste products and non-waste ions must be excreted each day

(Excreted even if no urine intake, therefore can urinate to death)

Question 11

What is the minimum urine concentration in man?

Answer 11

30-50mOsmoles/L (10x more diluted than plasma)

Question 12

The kidneys are able to produce urine of varying concentration because the loops of Henle of juxtamedullary nephrons act as …..

Answer 12

Counter current multiplyers

Question 13

What is the basic principle of counter current multiplers?

Answer 13

Fluid flows down descending limb and up ascending limb

Question 14

What are the 2 critical characteristics of the loops that make them counter current multiplers?

Answer 14

1. Ascending limb actively transports Na and Cl out of the tubule and into the interstitium and is IMPERMEABLE to water
2. Descending limb freely permeable to water but relatively impermeable to NaCl

Question 15

Describe in detail what happens at the loop of henle

Answer 15

1. NaCl actively transported out ascending limb
2. Osmolarity becomes greater in interstitum
3. Water from descending limb moves into interstitum
4. Water reabsorbed by high oncotic pressure + tissue pressure into vasa recta
5. As more + more concentrated fluid is delivered to ascending limb, interstitum becomes more concentrated

Question 16

The fluid in the tubule is progressively concentrated/diluted as it moves down the descending limb and progressively concentrated/diluted as it moves up the ascending limb.

Answer 16

Concentrated

Diluted

Question 17

Through use of the sodium channels how many mOsmoles of a difference are created between the ascending limb and the interstitium?

Answer 17

200

Question 18

How concentrated is the start of the descending limb vs the bottom of it?

Answer 18

300mOsmoles vs 1200 mOsmoles

Question 19

How does frusemide work?

Answer 19

Abolishes active transport NaCl from ascending limb so concentration differences are lost + kidney can only produce isotonic urine

Question 20

Is the fluid that enters the distal tubule more or less dilute than plasma?

Answer 20

More (fluid enters at 300mOsm + leaves at 100)

Question 21

The counter current mechansim concentrates/dilutes the medullary interstitum

Answer 21

Concentrates

Question 22

What are the vasa recta?

Answer 22

Specialised arrangement of peritubular capillaries at the juxtamedullary nephrons

Question 23

Are the vasa recta involved in the countercurrent mechanism?

Answer 23

Yeah as they act as countercurrent exchangers

Question 24

Why do the vasa recta not interfere with the gradient set up by the countercurrent mechanism?

Answer 24

They are arranged as hairpin loops (which follow the loop down) and are freely permeable with water and solutes so equibilirate with the medullary interstitial gradient

Question 25

What are the 3 main functions of the vasa recta?

Answer 25

Provide O2 for medulla
Do not disturb the gradient
Removes volume from interstitium (up to 36l/day)

Question 26

Why are the vasa recta able to reabsorb all this fluid?

Answer 26

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

Flow rate through vasa recta very low so plenty of time for equilibration to occur with interstitium

Question 27

Where is the site of water regulation in the kidneys?

Answer 27

Collecting duct

Question 28

What hormone is responsible for water regulation at the collecting duct?

Answer 28

ADH (vasopressin)