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Cardiovascular system

Published by Bupa's health information team, May 2009.

This factsheet is for people who would like information on how the cardiovascular system works.

The cardiovascular system is responsible for getting the constant supply of oxygen your body needs to the tissues that need it. It also helps removes carbon dioxide, a waste product, from tissues and transports it to the lungs where it's removed when you breathe out.

How the heart works

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About the cardiovascular system

Your cardiovascular system consists of your:

How does your cardiovascular system work?

Oxygen makes up about a fifth of the atmosphere. You breathe air through your mouth and nose and it travels to your lungs. Oxygen from the air is absorbed into your bloodstream through your lungs. Your heart then pumps oxygen-rich ('oxygenated') blood through a network of blood vessels - the arteries - to tissues including your organs, muscles and nerves, all around your body.

When blood reaches your tissues, through the capillaries, it releases oxygen, which is used by cells to produce energy. In exchange, these cells release waste products, such as carbon dioxide and water, which are absorbed and carried away by your blood.

The used (or 'deoxygenated') blood then travels along your veins and back towards your heart. Your heart pumps the deoxygenated back to your lungs, where fresh oxygen is absorbed, and the cycle starts once again.

The heart

Your heart is roughly the size of a clenched fist and weighs about 300g. It lies in the centre of your chest, surrounded by a protective membrane called the pericardium. In an average day, your heart pumps the equivalent of nearly 22,750 litres (5,000 gallons) of blood around your body.

Your heart is a muscular pump, divided into left and right sides, and its muscular walls squeeze (contract), pumping blood into the blood vessels and around your body.

The right side of your heart receives deoxygenated blood though the veins. This blood is pumped back to your lungs where it absorbs more oxygen. This oxygenated blood then returns to the left side of your heart, which pumps it out to the rest of your body through the arteries. The muscle on the left side of your heart is slightly larger because it has more work to do, pumping blood around your body.

Each side of your heart is divided into an upper chamber called an atrium and a larger, lower chamber, called a ventricle. Blood flows from each atrium to the ventricle below, through a one-way valve.

Illustration showing the main organs, arteries and veins in the cardiovascular system
The main organs, arteries and veins in the cardiovascular system

The lungs

Your lungs are positioned on either side of your heart in your chest cavity (thorax) and consist of spongy tissue with a rich blood supply.

Your diaphragm is a sheet of muscle that separates your chest from your abdominal cavity and forms the floor of your thorax. Movement of your diaphragm as you breathe in causes your lungs to inflate.

Air passes from your nose and mouth into the trachea (windpipe) and into each lung, through two airways called the bronchi. These divide into smaller airways, called bronchioles, which repeatedly divide and end in tiny sacs called alveoli. These are air sacs with walls just one cell thick. It's here that oxygen and carbon dioxide filters into and out of your blood. In this process, known as gaseous exchange, molecules of oxygen and carbon dioxide bind to the haemoglobin, a protein in your red blood cells.

There are about seven million alveoli in your lungs, which provide a vast surface area for gaseous exchange - around the size of a tennis court if it could be spread out.

In an average day, 10,000 litres of air can move in and out of your lungs.

Blood pressure

Blood carrying oxygen and nutrients is pumped around your body by your heart. As a result of this pumping action and the size and flexibility of your arteries that carry blood, the blood is under pressure. This blood pressure is an essential and normal part of the way your body works.

When blood pressure is measured, the result is expressed as two numbers, such as 120/80mmHg ("one hundred and twenty over eighty millimetres of mercury").

The first figure - the systolic blood pressure - is a measure of the pressure when your heart muscle is contracted and pumping blood. This is the maximum pressure in your blood system.

The second figure - the diastolic blood pressure - is the pressure between heart beats when your heart is resting and filling with blood. This is the minimum pressure in your blood system.

Your blood pressure should ideally be around 120/80mmHg.

If you have diabetes, ideally your blood pressure should be less than 130/80mmHg.

Your cardiovascular health

Your lifestyle plays an essential part in maintaining your long-term cardiovascular health. A healthy diet, moderate drinking, plenty of exercise, and stopping smoking can all help to maintain a healthy cardiovascular system.

Related topics

Further information

Sources

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: May 2009