Heart

These layers are surrounded by the pericardium, a thin outer lining protecting your heart. There are four chambers that make up the heart – two on the left side and two on the right.

The two small upper chambers are the atria. The two larger lower chambers are the ventricles. These left and right sides of the heart are separated by a wall of muscle called the septum.

Circulatory system: Your heart pumps blood around the body all the time – about five liters (eight pints) of it – and this is called circulation. Your heart, blood, and blood vessels together make up your cardiovascular system (or heart and circulatory system). The right side of the heart receives blood that is low in oxygen because most has been used up by the brain and body. It pumps this to your lungs, where it picks up a fresh supply of oxygen. The blood then returns to the left side of the heart, ready to be pumped back out to the brain and the rest of your body.

Blood vessels: Your blood is pumped around your body through a network of blood vessels:

• Arteries – they carry oxygen-rich blood from your heart to all parts of your body, getting smaller as they get further away from the heart

• Capillaries – they connect the smallest arteries to the smallest veins, and help exchange water, oxygen, carbon dioxide and other nutrients and waste substances between the blood and the tissues around them

• Veins – they carry blood, lacking in oxygen, back towards your heart, and get bigger as they get nearer your heart Blood vessels are able to widen or narrow depending on how much blood each part of your body requires. This action is partly controlled by hormones.

Valves: Your heart has four valves. They act like gates, keeping the blood moving in the right direction:

• Aortic Valve – on the left side

• Mitral Valve – on the left side

• Pulmonary Valve – on the right side

• Tricuspid Valve – on the right side

Electrical system  For your heart to keep pumping regularly, it needs electrical signals which are sent to the heart muscle telling it when to contract and relax.

The electrical signal starts in the right atrium where your heart’s natural pacemaker – the sinoatrial node – is situated. This signal crosses the atria, making them contract. Blood is pumped through the valves into the ventricles. Where the atria meet the ventricles, there is an area of special cells – called the atrioventricular node – which pass the electrical signals throughout your heart muscle by a system of electrical pathways, known as the conducting system.

The muscles of the ventricles then contract, and blood is pumped through the pulmonary and aortic valves into the main arteries. The heart’s natural ‘pacemaker’ – the sino-atrial node – produces another electrical signal, and the cycle starts again.

Blood pressure This is the measurement of the pressure within the arteries. It plays a vital role in the way your heart delivers fresh blood to all your blood vessels. For blood to travel throughout your body quickly enough, it has to be under pressure. This is created by the relationship between three things:

• Your heart’s pumping action

• The size and stretchiness of your blood vessels

• The thickness of the blood itself

One heartbeat is a single cycle in which your heart contracts and relaxes to pump blood. At rest, the normal heart beats approximately 60 to 100 times every minute, and it increases when you exercise. To ensure an adequate blood supply around your body, the four chambers of your heart have to pump regularly and in the right sequence.

There are two phases to your heart’s pumping cycle:

• Systole – This is when your heart contracts, pushing blood out of the chambers

• Diastole – This is the period between contractions when the muscle of your heart (myocardium) relaxes and the chambers fill with blood

Heart Problems Some things that may put you at a higher risk of coronary artery disease are:

• Age (For men, the risk of heart disease goes up after age 55; for women, the risk rises sharply after menopause.)

• Being inactive

• Having diabetes or metabolic syndrome

• Family history of coronary heart disease

• Genetics

• High blood pressure

• High levels of LDL “bad” cholesterol or low levels of HDL “good” cholesterol

• Obesity

• Smoking

• Stress