Week 2 - C - Physiology 5 - Countercurrent system in the kidney

Question 1

What is the gradient produced by the loop of henle due to the tubular reabsorption/secretion of substances?

Answer 1

Creates a corticomedullary solute concentration gradient in the interstitial fluid

Question 2

What type of urine does the corticomedullary gradient allow for the production of?

Answer 2

Allows for the production of hypertonic urine in the presence of ADH

Question 3

What is the opposing flow in the two limbs leading to the corticomedullary solute concentration gradient known as?

Answer 3

This is the countercurrent flow

Question 4

The loop of Henle works with what to establish a hyper-osmotic medullary interstitial fluid ?

Answer 4

Works with the vasa recta to establish this

Question 5

Descending limb (DL) of the loop of Henle This segment does not reabsorb NaCl and is highly permeable to water How does this differ from the ascending limb?

Answer 5

The ascending limb is impermeable to water however absorbs sodium and chloride

Question 6

How is it that the hyper-osmotic medullary interstitial fluid is set up then?

Answer 6

As there is no salt reabsorption in the desceing loop of Henle this makes the interstitial fluid at the bottom of the medullary portio of loop very osmotic Salt is then reabsorbed in ascending loop of Henle

Question 7

Easier way to understand it Imagine the loop of Henle is filled with isotonic fluid eg 300mosmol/l What would the sodium and chloride absorption in thick loop of henle cause? Why cant water counteract this?

Answer 7

Sodium and chloride is reabsorbed from the tubular lumen to interstitial fluid here therefore making the hypertonic interstitium As the ascending loop of Henle is impermeable to water, it cannot be reabsorbed into the ascending loop of Henle

Question 8

What is the main transporter in thick ascending loop of Henle to transport substances from tubular lumen into the tubular cells/interstitium?

Answer 8

This is the Na+/K+/2Cl- symporter where absorbs all three substances into the tubular cells

Question 9

What happens to the potassium once it is reabsorbed into the tubular cells?

Answer 9

It is then secreted back into the tubular lumen by different potassium channels

Question 10

K+ recycling means that NaCl is absorbed into the interstitial fluid What is the pump specific to the basolateral membrane of the tubular cell accounting for the reabsorption of Na into the interstitial fluid?

Answer 10

This is the Na+/K+,ATPase (sodium, potassium pump) pump which causes the reabsorption of sodium Also have a K+/Cl- contransporter which transports both into the interstituim however potassium is recycled

Question 11

What are the class of drugs which inhibit the Na+/K+/2Cl triple co-transporter?

Answer 11

These are the loop diuretics

Question 12

Triple co-transporter pumps solute from the thick ascending limb of Loop of Henle into the interstitial fluid What does this result in from the descending loop of Henle?

Answer 12

The descending loop of Henle responds by reabsorbing water into the interstitial fluid due to the osmosis Descending loop of Henle is impermeable to salt

Question 13

Once the hypotonic fluid in the thick ascending loop is formed, where does it move to?

Answer 13

It moves on to the distal tubule

Question 14

This process continues to occur. State how the process of countercurrent flow continues.

Answer 14

The fluid moves along the tubule And again the solute is reabsorbed via Na+/K+/2Cl- cotransporter at the apical membrane into the tubular cell and the Na+/K+/ATPase pump at the basoleteral membrane into the interstitium This causes an increase in intertsitial omsolarity leading to water reabsorption from the descedning limb

Question 15

Eventually the a steady state is reached in the loop of Henle, what is this steady state known as?

Answer 15

This is known as the corticomedullary solute concentration gradient

Question 16

Describe enters of iso, hypo, hyper what the fluid entering and leaving the loop of Henle is?

Answer 16

The fluid entering the loop of Henle is iso-osmotic and leaving the loop of Henle is hypoosmotic

Question 17

It is not only salt which contributes to the corticomedullary concnentration gradient Where else does the concentration gradient arise from?

Answer 17

Concentration gradient also arises from urea Urea along with salt contributes to the corticomedullary concentration gradient

Question 18

What percentage of urea is reabsorbed and from which part of the nephron?

Answer 18

50% of urea that is filtered is reabosrbed from the nephron

Question 19

The purpose of the countercurrent multiplication is to concentrate the medulary interstitial fluid Why is this?

Answer 19

This enables the kidney to produce urine of different volume and concentration in relevance to the quantity of ADH production (ADH = vasopressin)

Question 20

The volume of urine produced per day is roughly 1.5l/day What is the Vu? (remember, rate of urine flow) What can it increase and decrease to depending on ADH?

Answer 20

It is 1ml/min roughly Can decrease to 0.3ml/min and increase to 25ml/min

Question 21

What runs along the loop of Henle in juxtamedullary nephrons?

Answer 21

The vasa recta

Question 22

Omsolality of the blood will rise as it dips into the medulla and fall as it goes back into the cortex Why is this?

Answer 22

This is due to the vasa recta reaching an equilibrium state with the interstitial fluid and therefore when the omsolarity of the interstitial fluid changes, so does the vasa recta omsolality

Question 23

Vasa recta acts as a COUNTERCURRENT EXCHANGER Together, the Loop of Henlé and vasa recta form a COUNTERCURRENT SYSTEM. How does the vasa recta contribute?

Answer 23

Pssive exchange across the endothelium of the capillaries maintains the medullary gradient whilst ensuring that solutes are not washed away

Question 24

The countercurrent multiplier and the urea cycle create what?

Answer 24

The corticomedullary solute concentration gradient

Question 25

The countercurrent exchanger preserves that gradient What is the countercurrent exchanger? What forms the countercurrent system

Answer 25

The countercurrent exchanger is the vasa recta The loop of Henle together with the vasa recta forms the countercurrent system

Question 26

What does the high medullary osmolality allow for?

Answer 26

This allows for the production of hypertonic urine in the presence of ADH