2.2. The Loop of Henle - Post-Proximal Tubule

Question 1

What is the osmolarity of the fluid which leaves the proximal tubule?

Answer 1

It is isosmotic with plasma at 300mOsmoles/L

Question 2

Why is the osmolarity the same as plasma?

Answer 2

Due to the solute movements being accompanied by H2O movements

Question 3

Where is the system essential for water balance located?

Answer 3

In the juxtamedullary nephrons (loops of henle)

Question 4

What does the system essential for water balance allow for?

Answer 4

Urine concentration in times of deficit

Question 5

Where is the rest of the tubule found?

Answer 5

In the renal cortex

Question 6

What volume of urine must be secreted, even if there is no water absorption?

Answer 6

500mls

Question 7

Why must this volume of urine be excreted, even if there has been no water absorption?

Answer 7

To allow for the essential minimal waste products to be excreted

Question 8

What is the osmolarity of the minimal amount of waste products which must be excreted each day?

Answer 8

600mOsmoles

Question 9

What forms the wate products?

Answer 9

1. Urea
2. Sulphate
3. Phosphate
4. Non-waste ions (Na, K)

Question 10

What happens in condition of excess water intake?

Answer 10

water will be excreted in excess of the solute

Question 11

What is the minimum concentration of urine?

Answer 11

30-50mOsmoles/L

Question 12

How is the kidney able to produce varying concentrations of urine?

Answer 12

Due to the loops of Henle acing as counter-current multipliers

Question 13

What are the critical characteristics of the counter-current multipliers?

Answer 13

1. The ascending limb actively transports NaCl out of the lumen, but is impermeable to H2O
2. The descending limb is freely permeable to H2O but is relitively impermeable to NaCl