Substances are transported around the body by the circulation system (the heart, the blood vessels and the blood). They are transported from where they are taken into the body to the cells, or from the cells to where they are removed from the body.
There are two separate circulation systems, one to the lungs and one to all the other organs of the body.
- The heart pumps blood around the body.
- Blood flows from the heart to the organs through arteries and returns through veins.
- In the organs, blood flows through capillaries.
- Substances needed by cells in the body tissues pass out of the blood, and substances produced by the cells pass into the blood throught the walls of the capillaries.
Blood plasma transports:
- carbon dioxide from the organs to the lungs
- soluble products of digestion from the small intestine to other organs
- urea from the liver to the kidneys
Red blood cells
- Red blood cells transport oxygen from the lungs to the organs
- Red blood cells have no nucleus.
- They are packed with a red pigment called haemoglobin.
- In the lungs haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs oxyhaemoglobin splits up into haemoglobin and oxygen.