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Unlock This CourseThe heart is a muscular organ about the size of your fist that pumps blood around your body. It beats approximately 100,000 times per day, pumping about 7,500 litres of blood! The heart is located in the thorax (chest), between your lungs and is protected by the ribcage.
Key Definitions:
The heart is divided into four chambers - two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. The right side of the heart pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the body.
Right Atrium: Receives deoxygenated blood from the body via the vena cava.
Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.
Left Atrium: Receives oxygenated blood from the lungs via the pulmonary vein.
Left Ventricle: Pumps oxygenated blood to the body via the aorta.
The walls of the ventricles are thicker than the atria because they need to generate more pressure to pump blood further.
The left ventricle has the thickest walls because it needs to pump blood all the way around the body against higher pressure.
The right ventricle only needs to pump blood to the lungs, which are close by and have lower pressure.
Valves in the heart ensure that blood flows in one direction only. They open and close due to pressure differences on either side.
These valves sit between the atria and ventricles:
They prevent blood from flowing back into the atria when the ventricles contract.
These valves are found at the exits of the ventricles:
They prevent blood from flowing back into the ventricles when they relax.
Several major blood vessels connect to the heart, bringing blood in or taking it away:
Vena Cava: Returns deoxygenated blood from the body to the right atrium.
Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium.
Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
Aorta: Carries oxygenated blood from the left ventricle to the body.
Coronary Arteries: Supply the heart muscle itself with oxygen and nutrients.
Coronary Veins: Remove waste products from the heart muscle.
The heart functions as a double pump because it pumps blood through two separate circuits:
This is the shorter circuit where:
This is the longer circuit where:
The cardiac cycle refers to the sequence of events that occur during one heartbeat:
Coronary heart disease occurs when the coronary arteries become narrowed by a build-up of fatty material (atheroma). This reduces the blood supply to the heart muscle, which can cause chest pain (angina) or a heart attack if a coronary artery becomes completely blocked.
Risk factors include smoking, high blood pressure, high cholesterol, obesity and lack of exercise. Understanding the heart's structure helps explain why blockages in these small but vital arteries can have such serious consequences.
The heart's structure is perfectly adapted to its function:
In a laboratory setting, you might examine a heart specimen (often a sheep or pig heart, which is similar to a human heart). Key features to identify include:
The "lub-dub" sound of your heartbeat is actually the sound of your heart valves closing! The "lub" is the atrioventricular valves closing and the "dub" is the semilunar valves closing.
Your heart will beat about 2.5 billion times in an average lifetime!