Kidney: water 1 (reabsorption)

Question 1

2 types of H2O (water) passive reabsorption

Answer 1

• Obligatory water reabsoprtion
• Facultative water reabsorption

Question 2

Obligatory water reabsorption is responsible for ____% of water reabsorption

Answer 2

87% of water reabsorption

Independent of ADH (anti-diuretic Hormone)

Question 3

Describe Obligatory Water reabsorption in Proximal Convoluted tubule (PCT)

Answer 3

Solutes (Na+):
* reabsorption of 65% of Na+, which creates an osmotic gradient
Water (H2O):
* PCT is Highly permiable to water
* reabsorption, by osmosis, of 65% of water down osmotic gradient, through Aquaporin-1 Channels

Osmolarity:
* * Osomlarity inside lumen/tubular fluid osmolarity = to plasma osmolarity (iso-osmotic/isotonic) = 300m osmo/L

Question 4

Describe Obligatory Water reabsorption in Descending limb of loop of henle

Answer 4

Solutes (Na+):
* Descending is impermiable to Na+
* so no reabsoption of Na+

Water:
* Descending limb is highly Permiable to water
* Reabsoprtion of 15% of water, by osmosis
* this is due to Hyperosmotic medullary ISF

Osmolarity of tubular lumen:
* Osmolarity increases until it reaches equilibrium & becomes equal to Hyperosmotic Medullary ISF (1200-1400 m osmo/L)

Question 5

Describe Obligatory Water reabsorption in Ascending limb of loop of henle

Answer 5

Solutes (Na+):
* Reabsoprtion of solutes (via active transport)

Water:
* Ascending limb is impermiable to water
* No reabsorption of water

Osmolarity:
* Water stays inside
* solutes reabsorbed outside
* Osmolarity decreases inside tubular fluid (100m osmo/L)

Question 6

Describe Obligatory Water reabsorption in early part of Distal convoluted tubule of loop of henle

Answer 6

same as Ascending limb of loop of henle
* Solutes continue to be reabsoprbed
* impermiability to water, so water is not reabsoprbed
* Osmolarity continues to decrease inside tubular fluid= more diluted (60m osmo/L)

Ascending + early DCT are called diluting segments

Question 7

Obligatory Water reabsorption in Late DCT & Collecting duct is respsosible for ____% of water reabsoprtion

Answer 7

7%

ADH (hormones) are not the only cause of reabsorption in CD & late DCT

Question 8

Describe Facultative Water reabsorption & how it’s controlled by ADH

Answer 8

• Responsible for 13% of water Reabsoprtion
• occurs at late DCT & CD
• It depends on the body’s needs of water
• ADH increases water Reabsoprtion
• by Inserting aquaporin-2 Channels into luminal membrane of P (principal) cells
• Water then diffuses from basolateral border of P cells to ISF by aquaporin-3 & aquaporin-4

Question 9

function of Aquaporin 1

Answer 9

Obligatory Reabsoprtion of water at luminal border (at PCT, Descending limb of loop of henle, late DCT & CD)

Question 10

Function of Aquaporin 2

Answer 10

Facultative reabsorption of water at late DCT & CD

Question 11

Function of aquaporin-3,4

Answer 11

Diffusion of water from P cells into ISF at basolateral border