Controlling osmolarity

Question 1

When would you require diuresis and anti-diuresis?

Answer 1

Hypotonic - diuresis
Hypertonic - anti-diuresis

*dilute urine/loss excess water if fluid is already hypotonic

Question 2

Which parts of the nephron are diluting segments?

Answer 2

The LOH, DCT and the CT

Question 3

How does the LOH dilute the urine?

Answer 3

Variable sodium/water reabsorption in descending.

Ascending is impermeable to water and ions pumped out

Creates hypotonic filtrate and hypertonic medullary interstitium

Question 4

How do the DCT and the CT concentrate vs dilute urine?

Answer 4

Depends on permeability to water

Concentrate urine: Aquaporins
*water leaves CT as it passes into hypertonic medullary interstitium

Question 5

What do osmoreceptors do and where are they?

Answer 5

In Hypothalamus, shrink -> triggers thirst and ADH (from posterior pituitary)

ADH stimulates..

1. Aquaporins on basolateral side of DCT and CT -> more water resorption
   * not permanent due to quick membrane turnover
2. Vasoconstriction
   - > increase BP

Question 6

What is counter-current multiplication?

Answer 6

Ascending LOH impermeable to water and creates a hypertonic medullary interstitium via actively pumping out ions (Na-K-Cl cotransporter and Na-K-ATPase)

Descending LOH is permeable to water -> water leaves filtrate

Question 7

Is counter-current multiplication enough to keep an extreme hypertonic medullary interstitium?

Answer 7

Urea also recovered into interstitial fluid via DCT

*further concentrates medulla

Question 8

Explain how the blood supply fuels the kidneys without interrupting the process?

Answer 8

Vessels arranged in U shaped vasa recta (cortex - down into medulla-back up)

Question 9

Why does the kidney require 25% of cardiac output at rest?

Answer 9

Countercurrent multiplication requires a lot of ATP