5.2.6- The function of the kidney 2

Question 1

How much water is reabsorbed?

Answer 1

1) Every minute: 125cm3 filtered from the blood and enters the nephrons.
2) After selective reabsorption 45cm3 fluid is left
3) By the time this fluid reaches the bladder, volume dropped to about 1.5cm3

Question 2

What does the loop of henle consist of?

Answer 2

consists of a descending limb that desends into the medulla and an ascending limb that ascends back out to the cortex.

Question 3

What does the arrangement of the loop of Henle allow it to do?

Answer 3

1) Allows mineral ions ( Na+,Cl+) to be transferred from the ascending limb to the descending limb
2) Overall effect is to increase the concentration of mineral ions in the tubule fluid which has a similar effect upon the concentration of mineral ions in the tissue fluid. –> Gives the tissue fluid in the medulla a very negative water potential

Question 4

What occurs in the loop of Henle?

Answer 4

1) Mineral ions enter the descending limb, concentration of fluid in the descending limb rises. –> Water potential decreases (negative) –> Increasingly more negative deeper the tubule descends into the medulla
2) As fluid rises up ascending limb, mineral ions leave the fluid. Near the base diffusion, further up is active transport —> Upper portion of the ascending limb is also impermeable to water
3) Effect of these ionic movements is to create a higher water potential in the fluid of ascending limb. Also decreases the water potential in the tissue fluid of medulla –> Water potential of tissue fluid becomes lower towards bottom of loop of Henle
4) Fluid passes down collecting duct, passes through tissues with an every-decreasing water potential –> Always a potential gradient between fluid in collecting duct and that in tissues, –> Allows water to be moved out of the collecting duct and into the tissues through osmosis

Question 5

Why is the arrangement of the loop of henle referred to as the ‘hairpin counter current multiplier system,’?

Answer 5

Overall effect of this arrangement is to increase the efficiency of transfer of mineral ions from the ascending limb to the descending limb, in order to create the water potential gradient seen in the medulla.

Question 6

What happens in the collecting duct?

Answer 6

1) At this stage tubule fluid still contains a lot of water, has a high water potential
2) Collecting duct carries fluid back down through the medulla to the pelvis –>Medulla has low water potential
3) Water moves out by osmosis from the tubule fluid into surrounding tissues –> Enters the blood capillaries by osmosis and carried away
4) Amount of water that is reabosrbed depends on the permeability of the collecting duct walls.
5) By the time urine reaches pelvis it has a very negative water potential and the concentration of minerals and urea is higher than in blood.