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Cardiovascular system
The cardiovascular system supplies oxygen from the lungs to the tissues around the body. It also transports carbon dioxide, a waste product, from the body to the lungs. Breathing out removes carbon dioxide from the body.
How the heart works
About the cardiovascular system
How does your cardiovascular system work?
Your cardiovascular health
How the heart works
About the cardiovascular system
Your cardiovascular system is your:
• heart
• blood vessels – arteries, veins and capillaries (small blood vessels)
• blood
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 the capillaries in your tissues it releases oxygen, which cells use to make energy. These cells release waste products, such as carbon dioxide and water, which your blood absorbs and carries away.
The used (or 'deoxygenated') blood then travels along your veins and back towards your heart. Your heart pumps the deoxygenated blood back to your lungs, where it absorbs fresh oxygen, and the cycle starts again.
The heart
Your heart is roughly the size of a clenched fist and weighs about 300g. It lies just to the left in your chest, surrounded by a protective membrane called the pericardium.
Your heart is a pump, divided into left and right sides. It has walls, made of muscle, which squeeze (contract) to pump blood into the blood vessels and around your body. You have around 8 pints of blood in your body, and in an average day your heart beats 100,000 times to keep the blood moving around your body.
Your veins deliver deoxygenated blood to the right side of your heart. Your heart pumps this blood 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 than the right: the right side only pumps blood to your lungs, the left side pumps 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.
[Please insert illustration
The lungs
Your lungs are on either side of your heart in your chest (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 makes your lungs inflate.
Air passes from your nose and mouth into your 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 filter 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 300 million alveoli in each lung, 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, you breathe 10,000 litres of air in and out of your lungs.
Blood pressure
Blood carrying oxygen and nutrients is pumped around your body by your heart. The blood is under pressure as a result of the pumping action of your heart and the size and flexibility of your arteries. This blood pressure is an essential 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 vessels.
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 vessels.
The lower your blood pressure, the better for your health, although very low blood pressure can make you feel dizzy or faint. Doctors recommend that blood pressure is kept below 140/85. If you have diabetes, kidney disease or cardiovascular disease, your blood pressure should be lower than this – ideally less than 130/80.
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 not smoking can all help to maintain a healthy cardiovascular system.
This section contains answers to common questions about this topic. Questions have been suggested by health professionals, website feedback and requests via email.
What sorts of exercises can I do to keep my heart healthy?
I have diabetes and I have heard this can affect my heart. Do I need to take special precautions?
Can too much stress in my life really cause heart disease?
What sorts of exercises can I do to keep my heart healthy?
You can improve the health of your heart (your cardiovascular fitness) through different types of physical activity or exercises.
Explanation
The best kind of exercise for your heart is aerobic activity – this means that it involves or improves the use of oxygen by your body. This is essential for improving your cardiovascular fitness. Aerobic activity can be any repetitive exercise that involves the large muscle groups of your legs, shoulders or arms.
The recommended healthy level of physical activity is 30 minutes’ moderate exercise on at least five days each week. Moderate means your breathing is faster, your heart rate is increased and you feel warmer. At this level of activity, your heart and lungs are being stimulated and this goes towards making you fitter.
Good forms of cardiovascular exercise include running, aerobics, cycling and swimming. It's important to realise that exercise can also include all kinds of day-to-day activities such as:
• gardening
• climbing stairs
• walking
• vacuuming
If you are overweight or have a medical condition, check with your GP before starting an exercise programme. He or she will be able to advise you on the best way to increase your physical activity.
I have diabetes and I have heard this can affect my heart. Do I need to take special precautions?
If you have diabetes, you have a higher risk of developing heart disease. However, your GP can advise you how you can reduce your risk by making lifestyle changes and controlling your diabetes.
Explanation
If you have diabetes, you’re more likely to have high blood pressure and high levels of fats in your blood. Diabetes can also affect the heart muscle itself, making it a less efficient pump and making it more likely that you will develop heart disease. So, if you have diabetes, your GP will probably prescribe medicines to treat some of the risk factors that you may have. For example, he or she may give you medicines to lower your blood pressure and cholesterol level or aspirin to reduce the risk of blood clotting. If you smoke, your GP will also encourage you to stop smoking.
If you have high levels of triglycerides (a type of fat) and cholesterol in your blood, you have a greater risk of heart disease. The risk is particularly high if you also have a low level of HDL cholesterol (high-density lipoprotein, or 'good' cholesterol), which is more likely if you have diabetes. You may need to take a medicine known as a statin to reduce your cholesterol levels, and you may also need to have another medicine to control your triglyceride levels. Cutting down on fats in your diet, particularly saturated fats (which are found mostly in meat and dairy products), will also help.
High blood pressure is common in people with diabetes and it's important to control it. If you have diabetes, you should aim to have a blood pressure below 130/80mmHg, or lower than that if your kidneys are already damaged. You may be able to control your blood pressure by losing excess weight, doing more exercise and cutting down on alcohol and salt, although you may need to take medicines too.
Being physically active may help to reduce the amount of medicine or insulin you need to take for your diabetes, and can help reduce the risk of heart disease. It's important to monitor your blood glucose carefully as you start to build up your level of physical activity because you may need to change the dose of your medication. Your GP can advise you about this.
Can too much stress in my life really cause heart disease?
Stress isn't the only cause of heart disease but when combined with other risk factors, such as smoking, lack of physical activity, and high blood cholesterol, it can act to increase your risk of developing it.
Explanation
Many people think that heart disease is caused by years of stress. However, there is no evidence to show that stress alone causes heart disease, even though stress can cause your blood pressure to increase.
However, the way you try to cope with stress may increase your risk of developing heart disease. Stress can encourage less healthy behaviour, such as smoking, drinking too much alcohol, and over-eating.
Sources of stress can include relationships, work, health, financial problems, and major events such as moving house, bereavement or divorce.
A good way of identifying your sources of stress is to keep a diary and write in it when you are feeling stressed. This might help you to work out why you feel more stressed on some days than others. Once you have identified the possible causes of your stress, you can then take steps to tackle them and change how you respond to stressful situations.
If you can't change a source of stress, aim to try and change your attitude towards it. Think about how you respond when you find yourself in a stressful situation. Then try and think about how you could change both your physical and mental response to it.
A balanced diet and regular physical activity can help you to feel more ready to cope with potentially stressful situations. It's also important to learn how to relax – yoga and other relaxation techniques may help.
Talking to friends, colleagues or family members about any worries you have can help. If you think you are stressed or very anxious, talk to your GP who will be able to help you decide on the best way to deal with it.
Keywords Cardiovascular system, heart, lungs, blood, circulation, stress, heart disease, exercise, physical activity
Further information
• British Cardiovascular Society
020 7383 3887
www.bcs.com
• British Heart Foundation
0845 070 8070
www.bhf.org.uk
• HEART UK
0845 450 5988
www.heartuk.org.uk
Sources
• The heart – technical terms explained. www.bhf.org.uk, accessed 23 September 2010
• The way your lungs work. British Lung Foundation. www.lunguk.org, accessed 23 September 2010
• Simon C, Everitt H, van Dorp F. Oxford handbook of general practice. 3rd ed. Oxford: Oxford University Press, 2010: 253
• Blood pressure. British Heart Foundation. www.bhf.org.uk, accessed 23 September 2010
• CVD risk assessment and management. Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 23 September 2010
Related topics
• Angina
• Arrhythmia (palpitations)
• Chronic obstructive pulmonary disease (COPD)
• Coronary artery disease
• Deep vein thrombosis (DVT)
• Diagnosing heart conditions
• Healthy eating
• Heart attack
• Heart failure
• Heart valve disease
• High blood pressure
• High cholesterol
• Looking after your heart
• Sensible drinking
Published by Bupa's Health Information Team, November 2010.
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