Summary Ultrafiltration, Selective Reabsorption and Reabsorption of Water

Ultrafiltration, Selective Reabsorption, Reabsorption of Water:


 Ultrafiltration:
o The basement membrane acts as a filter.
o Water, glucose, mineral ions & other small molecules are
forced out of the capillary into the glomerular filtrate.
o The diameter of the afferent (coming in) arteriole is
greater than the diameter of the efferent (exiting)
arteriole, so there is a build up of hydrostatic pressure in
the glomerulus (network of capillaries) that forces fluid
into the renal capsule.
o The filtrate passes through the basement membrane and
then through the fenestrations in the podocytes.
o 125cm3 of blood is filtered each minute – this is the
glomerular filtrate rate (GFR).
o However lots of useful substances need to be reabsorbed
from the filtrate, this is done in the proximal convoluted
tubule (PCT).

 Selective reabsorption:
o In the PCT nearly 65% of the filtrate is reabsorbed back
into the blood,
o Cells of the PCT:
 Cuboidal epithelial cells.
 They have microvilli to create a large surface area.
 They have lots of mitochondria to provide ATP.
 The blood capillaries lie very close to the cells.