The circulatory system

The circulatory system, also known as the cardiovascular system, is critical to maintaining healthy organs, muscles and tissues. It delivers blood, which contains oxygen and nutrients, to all parts of the body and removes unwanted carbon dioxide and waste products.

The cardiovascular system consists of the heart and blood vessels.  The blood vessels work with the heart and lungs to continuously circulate blood around the body.

There are two circulatory systems in the body:

• Systemic circulation moves oxygen-rich blood from the lungs into the left side of the heart and is then pumped around the body for use
• Pulmonary circulation carries carbon dioxide-rich blood from your body back into your heart and then into your lungs to be exhaled

The heart

The heart is a muscle, about the size of a fist, in the middle of the chest and works like a pump sending blood around the body. 

The heart has a left and right side each with an upper and lower chamber.  The right side of the heart receives the deoxygenated blood that has just travelled around the body and pumps the blood to the lungs to collect a fresh supply of oxygen.  The left side of the heart pumps the reoxygenated blood around the body again.

The heart’s electrical system tells the heart when to contract and when to relax to keep blood pumping regularly. This is the heart rate and can change for example depending on emotions and if someone is active or resting. A normal resting heart rate is between 60 – 100 beats per minute but can vary due to age and health.

Like the rest of the body, the heart needs to be supplied with oxygenated blood to work properly which is provided by the coronary arteries spread across the outside of the heart. Sometimes the heart and circulatory system don’t work like they should which can cause heart and circulatory diseases, also called cardiovascular diseases, such as coronary heart disease (heart attack and angina) and stroke.

Composition of blood

Blood is made up of:

• Plasma which is approximately 90% water carrying platelets and red and white blood cells, and containing antibodies which fight infection
• Platelets that form blood clots to stop or prevent bleeding
• Red blood cells carrying oxygen from the lungs and delivering it throughout our body. They also transport waste such as carbon dioxide back to our lungs to be exhaled
• White blood cells which are part of the immune system manufacturing antibodies and fighting infection and bacteria

The blood vessels

• Arteries deliver oxygenated blood from the heart to the body except for the pulmonary artery which carries deoxygenated blood from the heart to the lungs
• Veins carry deoxygenated blood back to the heart
• Capillaries are much smaller blood vessels that form a link between the arteries, veins and body tissue to allow the transfer of oxygen and nutrients to the body and the removal of waste products