Your circulatory system works around the clock, with your heart acting as the pump that keeps blood moving throughout your body. Each heartbeat sends blood through a network of blood vessels, allowing oxygen and nutrients to reach your organs, muscles and tissues.
There are three main types of blood vessels, each with an important role. Arteries carry blood away from the heart, veins return blood towards the heart, and capillaries are tiny vessels where oxygen, nutrients and waste products are exchanged between the blood and surrounding tissues.
The circulatory and respiratory systems also work closely together. Blood travels to the lungs, where it releases carbon dioxide and takes up oxygen before returning to the heart to be pumped around the body.
This continuous process is known as circulation. It happens automatically, whether you're resting, walking, working or sleeping, helping your body carry out its normal everyday functions.