2.75B - Ultrafiltration

Edexcel IGCSE Biology

Where is blood filtered?

In the kidneys

What is the order of the reabsorption of key substances?

1. Ultrafiltration

2. Selective reabsorption of glucose

3. Reabsorption of water and salts

What is ultrafiltration?

Filtration of the blood which involves blood being forced out of the capillaries due to high pressure

What is the process of ultrafiltration?

1. Arterioles branch off the renal artery and lead to each nephron

   1. The arterioles form a knot of capillaries (glomerulus) which sits inside Bowman’s capsule

2. Capillaries get narrower as they go further into the glomerulus

3. This increases pressure on blood moving through

4. Pressure increase causes smaller molecules to be forced out the capillaries and into Bowman’s capsule

5. Smaller molecules form filtrate

6. Substance forced out of the capillaries contains: glucose, water, urea, salts

7. Some of these will be reabsorbed