Loop of Henle

Question 1

Where is the major site of reabsorption?

Answer 1

Proximal convoluted tubule

Question 2

What proportion of nutritional important substances are absorbed at the proximal tubule?

Answer 2

65-75%

Question 3

Which protein in particular can pass is small amounts though the proximal tubule and be reabsorbed?

Answer 3

Albumin

Around 0.5% of the total amount filtered at the glomerulus

Question 4

Are the majority of drugs and pollutants lipid soluble?

Answer 4

Yes, many are non polar and therefore highly lipid soluble

Question 5

What is the normal value of the proximal tubule osmolarity and that of the plasma?

Answer 5

300 mOsmoles/l

Question 6

What maintains the isosmocity of the proximal tubule with the plasma?

Answer 6

The equivalent H20 movements which accompany the solute movements, maintaining the osmotic equilibrium

Question 7

Where do ALL the proximal and distal tubules reside?

Answer 7

In the cortex

Question 8

What is the overriding role of the juxtamedullary nephrons?

Answer 8

Maintaining water balance

Question 9

What is the maximum level of concentration of urine that the kidneys can achieve?

Answer 9

1200-1400 mOsmoles/l

i.e. 4x more than plasma

Question 10

What is the bodies minimum obligatory H20 loss?

Answer 10

500mls per day - this occurs regardless of water intake (even in complete absence)

Question 11

Give some waste products which met be excreted each day

Answer 11

Urea
Sulphate
Phosphate

Question 12

What term is applied to the mechanism provided by the juxtamedullary apparatus which gives the kidney its ability to concentrate urine in line with fluid status?

Answer 12

Counter-current multipliers

Question 13

What are the two critical characteristics of the loops of Henle which make them counter-current multipliers? (one for ascending limb one for descending limb)

Answer 13

1. The ascending limb of the Loop of Henle actively co-transports Na+ and Cl- ions out of the tubule lumen into the interstitium. The ascending limb is IMPERMEABLE to H20
2. The descending limb is freely permeable to H20 but relatively impermeable to NaCl

Question 14

Describe the change in the concentrate of fluid as it passes through the LoH

Answer 14

It is concentrated as it goes down the loop - H20 leaves and NaCl enters

The high NaCl in this concentrated fluid loops round into the ascending limb and is then actively removed, and H20 added - and the concentration decreased

Question 15

Describe the concentration in the interstitium as fluid passes through the LoH

Answer 15

As water passes out of the descending limb the concentration of the interstitium decreases as it becomes more dilute, then when the concentrated fluid pass around into he ascending tubule, and the NaCl is excreted, the concentration in the interstitium increases. There is always a difference of 200 mOsmoles/l between two opposite levels in the ascending and descending limbs

Question 16

What is the key step of the LoH mechanism in maintaining the vertical concentration gradient in the interstitium?

Answer 16

The active transport of NaCl to of the ascending limb

Question 17

What is the end result of the counter-current mechanism system of the LoH?

Answer 17

To concentrate the medullary interstitium and deliver hypotonic fluid to the dial tubule

Question 18

What is the vasa recta? They are not countercurrent multipliers but…?

Answer 18

The specialised arrangement of the peritubular capillaries of the JG nephrons
Countercurrent exchangers

Question 19

What are the functions of the vasa recta?

Answer 19

1. Provide O2 for the medulla
2. In providing O2 it must not disturb the gradient
3. Removes volume from the interstitium - up to 36l/day

Question 20

What is the overall site of water regulation? What determines the permeability of this structure?

Answer 20

The collecting duct

ADH (vasopressin)

Question 21

What determines whether or not the dilute urine delivered to the distal tubule in concentrated, at to what extent?

Answer 21

The presence of the PP hormone ADH