Ultrafiltration: Ultrafiltration:
Occurs in the renal capsule.
The basement membrane acts as a filter.
Water glucose, mineral ions & other small molecules
are forced out of the capillary into the glomerular
filtrate.
The diameter of the afferent (coming in) arteriole is
greater than the efferent (exiting) arteriole, so there is a
build up of hydrostatic pressure in the glomerulus that
forces fluid into the renal capsule.
The filtrate passes through the basement membrane &
then through the fenestrations in the podocytes.
Selective Reabsorption: Selective Reabsorption:
Occurs in the proximal convoluted tubule (PCT) & in the
distal convoluted tubule (DCT).
Sodium-potassium pumps actively transport sodium out
of PCT cells & into the capillaries.
A low concentration of sodium ions in the cells cause
sodium ions to enter the PCT cells from the filtrate by
facilitated diffusion.
Glucose & amino acids are transported with the sodium
ions through cotransporter proteins into the PCT cells.
The glucose & amino acids then enter the blood
through facilitated diffusion.
The removal of solutes from the filtrate causes its water
potential to increase & the addition of solutes to PCT
cells & capillaries lowers their water potentials.
Water moves down the water potential gradient by
osmosis, through the PCT cells into the blood.
Urea enters the PCT cells passively by simple diffusion
since it is a small molecule.
Any large molecules (e.g. small proteins) will be
reabsorbed by endocytosis.
Occurs in the renal capsule.
The basement membrane acts as a filter.
Water glucose, mineral ions & other small molecules
are forced out of the capillary into the glomerular
filtrate.
The diameter of the afferent (coming in) arteriole is
greater than the efferent (exiting) arteriole, so there is a
build up of hydrostatic pressure in the glomerulus that
forces fluid into the renal capsule.
The filtrate passes through the basement membrane &
then through the fenestrations in the podocytes.
Selective Reabsorption: Selective Reabsorption:
Occurs in the proximal convoluted tubule (PCT) & in the
distal convoluted tubule (DCT).
Sodium-potassium pumps actively transport sodium out
of PCT cells & into the capillaries.
A low concentration of sodium ions in the cells cause
sodium ions to enter the PCT cells from the filtrate by
facilitated diffusion.
Glucose & amino acids are transported with the sodium
ions through cotransporter proteins into the PCT cells.
The glucose & amino acids then enter the blood
through facilitated diffusion.
The removal of solutes from the filtrate causes its water
potential to increase & the addition of solutes to PCT
cells & capillaries lowers their water potentials.
Water moves down the water potential gradient by
osmosis, through the PCT cells into the blood.
Urea enters the PCT cells passively by simple diffusion
since it is a small molecule.
Any large molecules (e.g. small proteins) will be
reabsorbed by endocytosis.
