Selective Reabsorption in the Proximal Convoluted Tubule

Question 1

How much filtrate is reabsorbed?

Answer 1

85%- all glucose and amino acids and some salts along with water

Question 2

Useful substances will be…

Answer 2

…‘reabsorbed’ from PCT into capillaries

Question 3

Process…

Answer 3

1.Na + actively transported out of cells of PCT through basal membranes
-high mitochondrial density for this
-K+ ions diffuse into to maintain electrochemical balance
2.As a result Na+ conc decreases
3.This creates conc gradient from filtrate in PCT down to cytoplasm of cells lining PCT
4.As a result, Na+ diffuses from lumen of PCT into cells via transporter proteins (co-transporter)
-glucose and amino acids are transported simultaneously
5.As a result of influx of solutes to cells of PCT, water potential in those cells decrease
-65%of water molecules move down gradient by osmosis, from nephron into blood
-urea also reabsorbed by diffusion due to its small size

Question 4

The loop of Henle function

Answer 4

-To create environment with low water potential
-Facilitate production of urine that it more concentrated than blood

Question 5

The counter-current multiplier…

Answer 5

…ensures tissue fluid in the medulla is of higher concentration (lower water potential) compared to filtrate in nephron

Question 6

The purpose of this ‘salt bath’…

Answer 6

…is to facilitate reabsorption of water from collecting duct

Question 7

2 adaptations of PCT

Answer 7

Covered in microvilli=greatly increasing surface area over which substances can be reabsorbed
Mitochondria=provide ATP needed in active transport system