Capillary Networks (WJEC GCSE Biology): Revision Note

Capillary Networks

• Organs are supplied with the blood they need through very small blood vessels called capillaries

• The substances required by the cells within organs move into the capillaries via diffusion; substances leaving the cells diffuse out of the cells and into the capillaries

• Capillaries also surround all exchange surfaces for example in the lungs and small intestine

Capillary networks surrounding the alveoli diagram

The blood vessels surrounding the alveoli in the lungs act as an exchange surface

• Capillaries are adapted to allow for efficient diffusion of substances and molecules through their walls

  • The walls are very thin, just one cell thick

  • A network of capillaries is formed around cells so that every cell is in close proximity to a capillary