The circulatory system

The heart is an organ that pumps blood around the body in a double circulatory system (blood passes through the heart twice in one complete circuit of the body):

• The right ventricle pumps deoxygenated blood to the lungs for gas exchange.

• Oxygen enters the blood and waste carbon dioxide leaves the blood.

• The left ventricle pumps oxygenated blood around the rest of the body where body cells use the oxygen for aerobic respiration to provide energy.

• Respiration also produces waste carbon dioxide, which is transported in the blood and exhaled via the lungs.

Heart rate: number of times a heart beats per minute.

Stroke volume: amount of blood ejected from the heart per heartbeat.

Cardiac output: volume of blood being pumped by the heart per minute (i.e. heart rate × stroke volume).