Blood

Why is blood so important?

• An adult has about 5 litres of blood. Although blood is liquid, it is also an organ containing many different types of specialised cells that carry out particular functions in your body
• These have all differentiated from blood stem cells and become specialised 

The composition of blood

• Blood is made up of four main components: plasma, red blood cells, white blood cells and platelets

• Plasma is a yellow liquid. It transports dissolved substances such as carbon dioxide, food substances and hormones

• Red blood cells contain the red pigment haemoglobin. Haemoglobin can combine reversibly with oxygen to form oxyhaemoglobin:

haemoglobin + oxygen = oxyhaemoglobin

• When blood passes through the lungs the haemoglobin combines with oxygen
• …