What is the heart?
The heart is a muscular pump but it is a very sophisticated one. It is made of muscle different from the sort that moves your arms and legs. Heart muscle is particularly strong as it has to cope with the physical and emotional stresses of normal daily life and, of course, it never takes a rest (you hope!). It beats on average 100 000 times every 24 hours and pumps out between 5 and 20 litres of blood (1 litre equals just under 2 pints) every minute, depending on your body’s needs – more when you are being active than when you are resting. Every organ in the body needs oxygen to function normally and efficiently. Fresh blood in the arteries delivers oxygen and energy to your body tissues and then, when it has given up its energy supply, blood carries away inthe veins unwanted waste products including carbon dioxide. The heart is the engine that pumps the blood around; normally it is the size of a clenched fist.
Can you tell me what the coronary arteries are?
these are the tubes or vessels that supply your heart muscle with the oxygen and energy that it needs to pump efficiently. The vessels that carry the oxygen round the body are called arteries. Coronary arteries* are tough tubes able to cope with the pressure pumped out by the heart. They are often confused with veins, such as those that we see on the back of the hand or on the legs (usually blue). Veins bring used-up blood back to the heart. They are thinner than arteries and do not work or cope with high pressure in the same way as arteries do.
Think of your coronary arteries like the branches of a big tree with a main trunk branching out into smaller and smaller branches and twigs. There are three important coronary arteries with many branches. There is a left coronary artery which divides into two large branches, and a right coronary artery which is usually one big vessel (see Figure 1.1). The coronary arteries arise from the main artery leaving your heart (the aorta), beginning just above the aortic valve (see question below). The most important coronary artery is the left . main stem, which controls both branches of the left coronary artery and, as a result, most of the blood supply to your heart muscle.
The coronary arteries start at about 3–4mm in size (like a thin straw) and as they feed the muscle they divide to reach all the layers of muscle. They run around the outside of the heart, sending their branches inwards.