Loop of Henle

Question 1

What happens to drugs that are lipid soluble?

Answer 1

The liver metabolizes them to polar compounds, which increases their permeability and facilitates their excretion

Question 2

What happens to the small amount of protein which reaches the glomerulus?

Answer 2

They are completely reabsorbed by a Tm mechanism in the proximal tubule

Question 3

What happens in the loop of henle?

Answer 3

Reabsorption only

Question 4

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

Answer 4

300mOsmoles/l (isosmotic with plasma)

Question 5

Where are the proximal and distal tubules located?

Answer 5

Cortex

Question 6

What is the special function of the juxtamedullary nephron loops of henle?

Answer 6

They allow the kidneys to produce concentrated urine in times of water deficit

Question 7

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

Answer 7

1200-1400mOsmoles/l (4x more concentrated than plasma)

Question 8

Which substances must be excreted every day?

Answer 8

Urea, sulphate, phosphate, waste products and non waste ions (Na and K)

Question 9

What is the osmolarity of the excreted substances and how much water is obligatory?

Answer 9

600mOsmoles and 500ml

Question 10

What is the minimum urine concentration?

Answer 10

30-50mOsmoles (10 fold diluted compared to plasma)

Question 11

How are the kidneys able to produce urine of varying concetrations?

Answer 11

Because the loops of henle of the juxtamedullary nephrons act as counter current multipliers

Question 12

How does a counter current work?

Answer 12

The fluid flows down the descending limb and up the ascending limb

Question 13

What are the critical characteristics of the loops which make them counter-current multipliers?

Answer 13

The ascending limb actively co-transports sodium and chlorine out of the tubule lumen and is impermeable to water
The descending limb is freely permeable to water and relatively impermeable to NaCl

Question 14

What is the maximum gradient in the loop of Henle?

Answer 14

200mOsm

Question 15

How does the concentration of the fluid in the tubule change as it passes through the loop?

Answer 15

It is progressively concentrated as it moves down the descending limb and progressively diluted as it moves up the ascending limb

Question 16

What happens to the concentration of urine when a diuretic (e.g. frusemide) is used?

Answer 16

The concentration differences are lost and can only produce isotonic urine

Question 17

What is the Vasa Recta?

Answer 17

The specialised arrangement of peritubular capillaries of the juxtamedullary nephrons

Question 18

What would happen if the medullary capillaries drained straight through?

Answer 18

They would carry away the NaCl removed from the loop of Henle and abolish the interstitial gradient

Question 19

What are the functions of the vasa recta?

Answer 19

Provides O2 for the medulla, does not disturb the gradient and removes volume from the interstitium

Question 20

Which part of the kidneys is responsible for water regulation?

Answer 20

Collecting duct

Question 21

Which hormone controls the permeability of the collecting duct?

Answer 21

Anti-diuretic hormone (ADH/vasopressin)

Question 22

Which factors affect the release of ADH?

Answer 22

Whether the dilute urine delivered to the distal tubule is concentrated and to what extent