Lecture 3

Question 1

What pathway is water reabsorbed?

Answer 1

Diffusion (osmosis) and is secondary to the reabsorption of sodium.

(Water follows sodium)

Question 2

Which section of the renal tubules is impermeable to sodium?

Answer 2

Descending limb of henle

Question 3

Whats happening in the ascending limb of henle in regards to sodium and water ?

Answer 3

Ascending limb of Henle, active transport of sodium (reabsorption)

25 % of filtered load

Ascending loop of henle is impermeable to water

Question 4

Why are we able to excrete urine that is more concentrated than our body fluids? The

Answer 4

We are able to concentrate urine (hyperosmotic) due to the medullary interstital hyperosmotic gradient.

Human kidney. Max [urine] = 1200mOsm/L
Typical daily excretion of solutes ~600mOsm/day

Minimum critical volume that we need to excrete in a day 500ml

Question 5

Most renal energy utilisation goes to accomplishing…

Answer 5

Reabsorption of sodium (active process)