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The heart

The heart is a muscular organ that pumps blood to the lungs and around the body.

The left and right sides of the heart are named from a first-person perspective. The left side of my heart is on the same side as my left arm.
The left and right sides of the heart are named from a first-person perspective. The left side of my heart is on the same side as my left arm.

The heart consists of two pumps that work together. The right side pumps deoxygenated blood to the lungs. The left hand side pumps oxygenated blood to the rest of the body.

The left side of the heart is more muscular than the right. This provides enough power to pump blood around the whole body.

Each side of the heart has two chambers:

  • Blood enters the heart through an atrium (plural atria).
  • Blood is pumped from the atria to the ventricles. The ventricles are larger the than atria.

The passage of blood is controlled by valves. Valves prevent blood from flowing in the wrong direction.

The tricuspid valve prevents blood from the right ventricle moving back into the right atrium.

The cardiac cycle is the series of heart muscle contractions that occur during a single heartbeat.

  1. During diastole, the atria and ventricles relax. Blood flows into the left and right atria.
  2. During atrial systole, the atria contract. Pressure in the atria becomes greater than in the ventricles. The atrioventricular valves (mitral and tricuspid) open and blood flows into the ventricles.
  3. During ventricular systole, the ventricles contract. Pressure in the ventricle becomes greater than in the atrium.

    This forces the atrioventricular valves to close and the semilunar valves to open. Blood flows out of the heart (via pulmonary artery and aorta).

The ventricles undergo a much larger pressure than the atria during the cardiac cycle.
The ventricles undergo a much larger pressure than the atria during the cardiac cycle.

The opening and closing of the heart valves depends only on the pressure difference between the two sides of the valve.

The closing of valves creates the 'lub-dub' sounds you hear when you listen to someone's heart. The 'lub' is the atrioventricular valves closing and the 'dub' is the semilunar valves closing.

The cardiac cycle is often displayed by the changes in pressure that occur during the cycle.

The heartbeat in this diagram lasts for approximately 1 second.
The heartbeat in this diagram lasts for approximately 1 second.
  1. Atrial systole : blood pressure rises when the atria contract, then falls while the blood is pumped into the ventricles. Once the blood has left the atria, the atrioventricular valves shut.
  2. Ventricular systole : once the atrioventricular valves shut, the blood pressure in the ventricles rises steeply while they contract (systole). When the semilunar valves open, the pressure is equalised with the aorta.
  3. Diastole : the semilunar valve shuts and the heart relaxes, allowing the pressure in the ventricles to fall. The blood pressure in the atrium slowly rises as it is filled with blood entering the heart.

Remember that the same contractions happen on both sides of the heart simultaneously.

Coronary heart disease is the general term for the narrowing of the arteries in the heart muscle.

Heart muscle is supplied with blood via coronary arteries. Coronary heart disease narrows the lumen of coronary arteries and stiffens their walls, increasing the chance of clotting.

If a coronary artery is blocked, insufficient blood will reach the heart muscle. This can cause a heart attack.

Several risk factors increase the risk of heart disease:

Risk factor Effects Prevention
Diet Fatty diets increase cholesterol levels Eat less fatty foods
Smoking Nicotine increases fat and cholesterol deposition in arteries Don't smoke
Lack of exercise Increases blood pressure and cholesterol Regular exercise
Stress Not fully understood
Inheritance Some people are genetically more prone to heart disease Not preventable
Cardiovascular disease is caused by the build-up of fatty deposits on the coronary artery walls.
Cardiovascular disease is caused by the build-up of fatty deposits on the coronary artery walls.