Ultrafiltration

Where does ultrafiltration take place

In the nephrons’ renal capsule

What is ultrafiltration powered by

The high hydrostatic pressure from the blood coming through into the renal artery from the aorta then into the renal arteriole

How does blood enter the renal capsule

Through the afferent arteriol

How does the blood leave the renal capsule

Through the efferent arteriole

How does the afferent arteriole differ from the efferent arteriole and how does it aid ultrafiltration

The lumen of the efferent arteriole is much smaller than the afferent arteriole so causes a build up of hydrostatic pressure of the highly convoluted capillaries of the glomerulus inside the renal capsule

What are the three layers through which the glomerular filtrate passes through

• endothelium of the capillary

• The basement membrane

• The epithelium cells of the capsule (podocytes)

How is the endothelium of the capillary adapted for ultrafiltration of the blood

It has tiny pores (fenestrations) which are too small for cells and plasma proteins to leave the blood.

What is the role of the basement membrane

Acts as a filter

What is the limit of Mr for molecules to pass through the basement membrane

68000g/mol

What is the name of the cells that line the capsule wall

Podocytes

What is the role of podocytes and how are they adapted to their role

They have feet like extensions that form a network with tiny slits between them called filtration slits through which fluid can pass into the lumen of the renal capsule (the glomerular filtrate is very similar to blood plasma but with protein molecules missing)

What is the glomerular filtration rate

The rate at which fluid filters from the capillary to the renal capsule (125cm³/min)

What is the glomerular filtration rate determined by

The difference in water potential between the plasma in the glomerular capillaries and filtrate in Bowman’s capsule

Overall the effect of pressure outweighs the effects of solute concentration so fluid continues to move out of capillary into capsule