Tubular function 3

Question 1

What environment is needed for the reabsorption of water?

Answer 1

hyperosmotic environment

Question 2

What is the difference between osmolarity and osmolality

Answer 2

OSMOLALITY - no. solute particles in 1kg water

OSMOLARITY - no. solute particles in 1L water

Question 3

Where is the hyperosmotic environment in the kidney?

Answer 3

Descending limb of loop of henle

Question 4

Explain countercurrent multiplication.

Active reabsorption of what molecule is important for countercurrent multiplication?

Answer 4

2 parallel loops of henle, with fluid moving through in opposite direction with different permeabilities too. This creates a hyperosmotic medullary interstitium. Primary force is active transport NaCl in ascending thick limb

Question 5

How does urea recycling lead to increased water absorption?

Answer 5

concentrates urea. diffuses passively (UT1) out of nephron and into interstitium and loop of henle. urea is trapped in thick loop of henle
contibutes to osmolality that drives water reabsorption

Question 6

Of the vasa recta, in terms of H2O and solutes, how do they move in the:
Descending limb?
Ascending limb?

Answer 6

Descending - H2O diffuses out and solutes into the vessels.

Ascending - H2O diffuses back in and solutes out of the vessels.

Question 7

Deep in the medulla, what is the pO2 and pCO2 ?

Answer 7

Low pO2 and high PCO2 bc of countercurrent arrangement

Question 8

What 2 mechanisms regulate osmolality?

What 2 things stimulate thirst and ADH secretion?

Answer 8

Thirst and ADH
Thirst - stimulated by inc osmolality and dec blood volume/pressure
ADH - stimulated by inc osmolality and dec blood volume/pressure

Question 9

What’s the osmotic threshold for ADH release?

Answer 9

~280-290mOsm/kg

Question 10

What can cause massive release of ADH?

Answer 10

severe blood loss

Question 11

Where is ADH synthesised?

What are the 4 main actions?

Answer 11

Posterior pituitary neurohypophysis. Triggered by baroreceptors and osmoreceptors

1. Inserts AQP2 at CD
2. Inserts splanchnic vasoconstrictor (ADH is also a vasoconstrictor but normally expressed at lower plasma levels than those having cardiovascular effects)
3. Inhibits renin T1 at CD
4. medullary collecting duct urea permeability

Question 12

Equation to find:
Total Solute?
Osmolality?

Answer 12

TS = fluid mass x osmolality 
O = solute/mass