Loop of Henle

Question 1

What is the function of the proximal tubule

Answer 1

Major site of reabsorption, 65-75% of all NaCl and H2O all nutritionally important substances.

Question 2

How does the liver help in excretion of Drugs and pollutants

Answer 2

The liver metabolizes them to polar compounds thus reducing their permeability and facilitating their excretion.

Question 3

What osmolarity is the filtrate that comes from the proximal tubule heading into the loop of henle?

Answer 3

300 mOsM/L

the same as plasma because all solute movements are accompanied by equivalent H20 movements - osmotic equilibrium is maintained

Question 4

What is a nephron?

Answer 4

A nephron is the microscopic structural and functional unit of the kidney.

It is composed of a renal corpuscle (glomerulus and capillaries) and a renal tubule.

ALL of the nephrons have their proximal and distal tubules in the Cortex and all nephrons have common processes for the reabsorption and secretion of solutes of the filtrate.

Question 5

The loops of henle of juxtamedullary nephrons are essential for which important process?

Answer 5

Water balance

Question 6

How do humans survive without water?

Answer 6

The kidney is able to produce concentrated urine in times of H2O deficit, however, as humans our ability to save water isn’t very good

Question 7

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

Answer 7

1200-1400 mOsmoles/L

Question 8

How many ml of H20 will every person lose in a day no matter what if their kidneys are functioning normally?

Answer 8

500 ml (doesn’t include sweating)

Question 9

What is the minimum urine concentration in humans?

Answer 9

30-50 mOsmoles/L (very diluted urine)

Question 10

What is the range of osmolarities that urine can be within in humans?

Answer 10

30-50 to 1200-1400 mOsmoles/l

Question 11

Characteristics of the ascending limb of the loop of henle?

Answer 11

It actively co-transports Na+ and Cl- ions out of the tubule lumen into the interstitium.

The ascending limb is impermeable to H2O.

Question 12

Characteristics of the descending limb of the loop of henle?

Answer 12

The descending limb is freely permeable to H2O but relatively impermeable to NaCl.

Question 13

What happens to the osmolarity inside the tubule and the interstitium when NaCl is actively pumped out of the ascending tubule

Answer 13

The osmolarity decreases inside the tubule but increases in the interstitium

Question 14

What happens in the descending tubule as a result of active transport of NaCl?

Answer 14

The descending limb is now exposed to greater osmolarity in the interstitium, H2O will move out to equate the osmolarity.

H2O does not stay in the interstitium, but is reabsorbed by the high oncotic and tissue pressures into the vasa recta (Starling’s forces).

Question 15

What is the vasa recta?

Answer 15

The specialised arrangement of the peritubular capillaries of the juxtamedullary nephrons.

They also participate in the countercurrent mechanism by acting as countercurrent exchangers.

Question 16

What happens as fluid moves through the loop of henle?

Answer 16

Concentrated fluid in descending limb rounds the bend and delivers a [high] to the ascending limb.

NaCl is actively removed again which further concentrates the interstitium and exposes the descending limb again to a greater osmolarity. This cycle repeats.

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

Question 17

At any horizontal level of the loop of henle what is the osmolarity gradient difference between the ascending limb and the interstitium ?

Answer 17

200 mOsmol

Question 18

What does the vertical gradient in the interstitium go from?

Answer 18

300-1200 mOsmol

Question 19

The loop of henle is in which part of the kidney?

Answer 19

The medulla

Question 20

How can the active transport of NaCl be abolished/stopped?

Answer 20

The use of a diuretic e.g furosemide/frusemide

Question 21

What happens if you take a diuretic like furosemide?

Answer 21

Unable to establish gradient because the diuretic switches off all the active transporters + all the ATP driven processes.

This means that salt (NaCl) is not being reabsorbed so doesn’t move into the interstitium and as a result there is no H20 movement so the filtrate fluid isn’t being concentrated as normal.

The kidney can only produce isotonic urine. Diuretics make you pee more essentially.

Question 22

How is the fluid ‘diluted’ in the ascending tubule?

Answer 22

By removing NaCl not by adding H20

Question 23

What osmolarity is the fluid that reaches the distal tubule?

Answer 23

About 100 mOsmole = hypotonic - lower concentration of solutes

Question 24

What are the key functions of the loop of henle?

Answer 24

To concentrate the medullary interstitium

To deliver hypotonic fluid to the distal tubule

Question 25

How come the medullary capillaries don’t interfere with the gradient

Answer 25

Due to their structure/arrangement - they are arranged as hairpin loops and therefore do not interfere with the gradient.

As with all capillaries, the vasa recta are freely permeable to H2O and solutes and therefore equilibrate with the medullary interstitial gradient at each level.

The flow rate through the vasa recta is very low (due to length and small diameter) so that there is plenty of time for equilibration to occur with the interstitium, further ensuring that the medullary gradient is not disturbed.

Question 26

Functions of the vasa recta (2)

Answer 26

Provide O2 for medulla - In providing O2 must not disturb gradient.

Removes volume from the interstitium, up to 36l/day.

Question 27

In terms of vasa recta H2O out and NaCl in occurs in which limb

Answer 27

Descending

Question 28

In terms of vasa recta NaCl out of the tubule occurs in which limb?

Answer 28

Ascending - this is most important to get water back into blood.

NaCl moves into the interstitium causing H2O to move out of the descending limb into the interstitium. H2O doesn’t stay in the interstitium but moves into the blood.

Question 29

What is the site of water regulation?

Answer 29

The collecting duct