Loop of Henle

Question 1

What is the major site for reabsorption?

Answer 1

Proximal tubule

Question 2

What protein is reabsorbed?

Answer 2

Albumin primarily

Question 3

How does the body excrete drugs?

Answer 3

Many are nonpolar and ∴ highly lipid soluble so that the removal of H2O in the proximal tubule establishes concentration gradients for their reabsorption. Because of their lipid solubility would never get rid of them! However the liver metabolizes them to polar compounds thus reducing their permeability and facilitating their excretion.

Question 4

How does the fluid in the proximal tubule compare in osmolarity to plasma?

Answer 4

The fluid that leaves the proximal tubule is isosmotic with plasma ie 300 mOmoles/L

Question 5

What is the maximum concentration of human urine the kidneys can produce?

Answer 5

1200-1400mOsmoles/L

i.e. 4x more concentrated than plasma = excess of solute over water

Question 6

What is the maximum concentration of desert species urine the kidneys can produce?

Answer 6

Desert species can produce urine as concentrated as 6000mOsmole/l, all H2O needs can be met by metabolic H2O

Question 7

What is the minimum concentration of human urine the kidneys can produce?

Answer 7

30-50 mOsmoles/L

i.e. 10 fold dilution compared with plasma.

Question 8

What is the minimum obligatory H20 loss required to clear waste products and substrates that must be removed daily?

Answer 8

minimum obligatory H2O loss of 500mls.

Question 9

What are the characteristics of loops of henle that make them counter-current multipliers?

Answer 9

o 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 H2O.

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

Question 10

What drug prevents active Na transport out of the ascending limb of the loop of henle?

Answer 10

Frusemide

Question 11

What are the vasa recta and what roles do they play in the kidneys?

Answer 11

The Vasa Recta: The specialized arrangement of the peritubular capillaries of the juxtamedullary nephrons; also participate in the countercurrent mechanism by acting as countercurrent exchangers.

Question 12

What are the functions of the vasa recta?

Answer 12

o Provide O2 for medulla.
o In providing O2 must not disturb gradient.
o Removes volume from the interstitium, up to 36L/day.

Question 13

What site in the kidneys is responsible for water reabsorption?

Answer 13

Collecting duct - permeability is under control by ADH

Question 14

What hormone is necessary for water balance?

Answer 14

ADH/vasopressin