B3- The Circulatory System

The Blood

Blood has four components-platelets (bits of broken cell), plasma, white blood cells and red blood cells.

Platelets clump together when a blood vessel becomes damaged in order to produce a clot.

Plasma transports several substances around the body including foods like glucose, water, hormones, antibodies and waste products.

White blood cells protect the body against disease. Some have a flexible shape which allows them to engulf disease-causing microorganisms.

Red blood cells transport oxygen from the lungs to the tissues. They: are small and flexible, so they can pass through narrow blood vessels and don't have a nucleus, so they can be packed with haemoglobin. The small size and biconcave shape of red blood cells gives them a large surface area to volume ratio for absorbing oxygen. When the cells reach the lungs, oxygen diffuses from the lungs into the blood. 

The haemoglobin molecules in the red blood cells bind with the oxygen to form oxyhaemoglobin. The blood is then pumped around the body to the tissues, where the reverse reaction takes place. Oxygen is released which diffuses into cells.

The Circulatory System

Blood moves around the body in arteries, veins and…