# Blood and Blood Vessels

Source: https://projectgcse.co.uk/biology/human_biology/blood_and_blood_vessels

> The contents of blood including red blood cells, white blood cells, platelets and plasma

The following are found inside the blood:

#### Red blood cells

- These contain haemoglobin which transport the oxygen to cells around the body.
- They have a large surface area so they can transport more oxygen.
- They also have a dent in them which makes them more flexible to fit through small blood vessels.

#### White blood cells

- These cells fight infection.
- They make antibodies to surround and overcome bacteria.
- Some white blood cells change shape to engulf bacteria.

#### Platelets

#### Plasma

- This is the yellow part of the blood.
- It contains many substances dissolved in it such as the products of digestion.

### BLOOD VESSELS:

#### Artery

- Thick and muscular with only a small hole through the middle so that it can withstand high pressure.
- The arteries carry blood with high levels of oxygen from the heart around the body.

#### Vein

- Thinner wall than the artery and it has lower pressure but a larger space inside.
- The veins also contain valves to prevent the blood from flowing the wrong way

#### Capillary

- Very thin wall which is only one cell thick.
- They pass close to cells and allow the blood to leak in and out of them.