How the circulatory system works

Your heart is an amazing organ. It continuously pumps oxygen and nutrient-rich blood throughout your body to sustain life. This fist-sized powerhouse beats (expands and contracts) 100,000 times per day, pumping about 4.7 to 5.7 litres (8 to 10 pints) of blood each minute, or about 7,570 litres (13,300 pints) per day.

How does blood travel through the heart?

As the heart beats it pumps blood through a system of blood vessels, called the circulatory system. The vessels are elastic tubes that carry blood to every part of the body.

Blood is essential. In addition to carrying fresh oxygen from the lungs and nutrients to your body's tissues, it also takes the body's waste products including carbon dioxide away from the tissues. This is necessary to sustain life and promote the health of all the body's tissues.

There are three main types of blood vessels:

• Arteries. They begin with the aorta, the large artery leaving the heart. Arteries carry oxygen-rich blood away from the heart to all of the body's tissues. They branch several times, becoming smaller and smaller as they carry blood further from the heart and into organs.
• Capillaries. These are small thin blood vessels that connect the arteries and the veins. Their thin walls allow oxygen, nutrients, carbon dioxide and other waste products to pass to and from our organ's cells.
• Veins. These are blood vessels that take blood back to the heart. This blood lacks oxygen (oxygen-poor) and is rich in waste products that are to be excreted or removed from the body. Veins become larger and larger as they get closer to the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.

This vast system of blood vessels - arteries, veins and capillaries - is over 96,550km (60,000 miles) long. That's long enough to go around the world more than twice!

Blood flows continuously through your body's blood vessels. Your heart is the pump that makes it all possible.

Where is your heart and what does it look like?

The heart is located under the rib cage, to the left of your breastbone (sternum) and between your lungs.

Looking at the outside of the heart, you can see that the heart is made of muscle. The strong muscular walls contract (squeeze), pumping blood to the arteries. The major blood vessels that enter the heart are the aorta, the superior vena cava, the inferior vena cava, the pulmonary artery (which takes oxygen-poor blood from the heart to the lungs where it is oxygenated), the pulmonary vein (which brings oxygen-rich blood from the lungs to the heart) and the coronary arteries (which supply blood to the heart muscle).