The heart
The structure of the heart
The heart is a muscular pump with four chambers:
- two at the top, which receive blood coming into the heart
- two at the bottom, which pump blood out of it.
The is the wall dividing the right side from the left side. Valves stop blood flowing backwards: the on the right and the on the left, between each atrium and ventricle, and the where blood leaves the ventricles.
The diagram shows the heart from the front, so its right side is on the left.
Key terms
The pathway of blood through the heart
- Deoxygenated blood from the body enters the through the .
- It passes through the into the .
- The right ventricle pumps it through a into the , to the lungs, where it picks up oxygen.
- Oxygenated blood returns through the into the left atrium.
- It passes through the into the left ventricle.
- The left ventricle pumps it through a semilunar valve into the , to the body.
The left ventricle has the thickest wall, because it pumps blood all round the body.
Remember
The right side carries deoxygenated blood; the left side carries oxygenated blood.
Heart rate, stroke volume and cardiac output
- is the number of times the heart beats per minute, in beats per minute (bpm).
- is the volume of blood pumped out of the left ventricle in one beat, in millilitres (ml).
- is the volume of blood pumped out of the left ventricle in one minute, usually in litres per minute (l/min).
Cardiac output = stroke volume × heart rate
Rearranged: heart rate = cardiac output ÷ stroke volume, and stroke volume = cardiac output ÷ heart rate.
Key terms
Worked examples
At rest: a person has a stroke volume of 70 ml and a heart rate of 70 bpm.
Cardiac output = 70 ml × 70 bpm = 4,900 ml/min. Divide by 1,000 to change millilitres to litres: 4.9 l/min.
During exercise: a swimmer has a cardiac output of 7,000 ml/min and a stroke volume of 70 ml.
Heart rate = cardiac output ÷ stroke volume = 7,000 ÷ 70 = 100 bpm.
These are typical values: everyone's are different.