Ultrafiltration

Urea is removed from the blood by the kidney nephrons by what process?

Ultrafiltration.

Why is the blood arriving at the capillaries of the glomerulus via the afferent arteriole at a high pressure?

• The heart’s contraction increases the pressure of arterial blood.

• The afferent arteriole has a wider lumen than the efferent arteriole– this difference increases the hydrostatic pressure of the blood plasma.

The blood entering the glomerulus is separated from the space inside the Bowman’s capsule by how many layers?

3 layers.

State the layers that separate the space inside the Bowman’s capsule from the blood in the glomerulus.

1. The wall of the capillary is a single layer of endothelium cells, with pores called fenestrae.

2. The basement membrane- acts as a selective barrier between the blood and the nephron.

3. The walls of the Bowman’s capsule is made of squamous epithelial cells called podocytes. Processes from each podocyte, called pedicels, wrap around the capillary, pulling it closer to the basement membrane. The gaps between the pedicels are called filtration slits.

Explain how the efficiency of filtration is increased.

• ‘Feet’ of the podocytes which increase surface area for filtration.

• Short distance between the podocytes and the capillary – this decreases the distance that substances have to travel between the blood and the filtrate – the contents of the Bowman’s capsule.

Why are small molecules forced out the blood and into the Bowman’s capsule?

Due to the high blood pressure of the glomerulus- solutes and water are forced through the fenestrae of the capillaries, through the basement membrane and through the filtration slits between the pedicels into the cavity of the Bowman’s capsule.

What does the glomerular filtrate (solutes and water forced into the Bowman’s capsule) contain?

• Water

• Glucose

• Salts

• Urea

• Amino acids

Why are blood cells, platelets and plasma proteins not filtered out?

They are too large- remain in the blood instead.