Urine Concentration

Question 1

Countercurrent multiplication system

Answer 1

Process in which a small osmotic gradient established at any level of LOH is multiplied into larger gradient. Single effect, due to movement of solute out of water impermeable asc limb.

As tubular fluid enters deeper layers of medulla, it is more concentrated that creates increasing gradient of osmolality, axial gradient.

Question 2

Countercurrent exchange system

Answer 2

Exchange of salutes and water takes place passively b/w asc and desc limbs of vasa recta, decreasing dissipation of solute gradient from medullary interstitium.
Water removed, exchanged.

Question 3

Countercurrent mechanism

Answer 3

Depends of generation and maintenance of increasing osmolality gradient along medullary pyramid from its outer to deepest layer.
Generated by LOH, maintained by vasa recta.
Collecting duct contributes by equilibrium for the gradient.

Question 4

Loop of Henle

Answer 4

Counter current multiplier. Selective reabsorption. Descending limb, increasing osmolality.
Thin ascending limb passive transport of solutes.
Thick ascending limb, active transport, Na-K ATPase.
Depends on length.

Question 5

Role of collecting duct

Answer 5

Permeability to water, and urea.
Water moves out, makes tubular urine hypertonic.
Urea some of it reab in PCT, everywhere else impermeable, therefore by the time in collecting duct, urea conc very high. Moves passively from tubular fluid to interstitium. Therefore water also moves.

Question 6

Role of vasa recta: the counter current exchanger system

Answer 6

Osmolal gradient is maintained by vasa recta.
In desc, solutes diffuse in, in asc, solutes diffuse out.
Movement of water opposite.