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