VMBO Year 2 · HAVO/VWO Years 2–3 · Circulation · Section 3.3
The heart
Heart structure
The heart is a hollow muscular organ. Coronary arteries, branching from the aorta, supply the heart muscle with oxygen and nutrients.
Coronary veins drain blood carrying carbon dioxide and waste products, mostly towards the right atrium through the coronary sinus.
A septum separates the right and left sides. Each side has an upper atrium and a lower ventricle.
Blood flow through the heart
Deoxygenated blood returns from the body through the superior and inferior vena cava to the right atrium, then enters the right ventricle.
The right ventricle pumps it through the pulmonary arteries to the lungs. After gas exchange, oxygenated blood returns through the pulmonary veins to the left atrium, then enters the left ventricle.
The left ventricle pumps it into the aorta, which supplies the body.
Atrioventricular valves between atria and ventricles prevent backflow towards the atria. Semilunar valves at the exits into the pulmonary artery and aorta prevent blood flowing back into the ventricles.
How the heart beats
A typical adult resting heart rate is around 70 beats per minute, but age, fitness and activity affect it. A simplified heartbeat has three phases:
- Atrial contraction: Both atria contract, pushing more blood into relaxed ventricles. Atrioventricular valves are open and semilunar valves are closed.
- Ventricular contraction: Ventricles contract, atrioventricular valves close and pressure rises. When ventricular pressure exceeds arterial pressure, semilunar valves open and blood enters the arteries. The atria relax.
- Relaxation and filling: Atria and ventricles relax. Blood returns through the venae cavae and pulmonary veins. Semilunar valves close; atrioventricular valves open once pressure permits filling.
Glossary
- Aorta
- The main artery carrying oxygenated blood from the left ventricle to the body.
- Superior vena cava
- The large vein returning blood mainly from the head, arms and upper body to the right atrium.
- Semilunar valves
- Valves at the ventricular exits into the pulmonary artery and aorta, preventing backflow into the ventricles.
- Atrioventricular valves
- Valves between atria and ventricles, preventing backflow into the atria.
- Relaxation phase
- The part of the heartbeat during which chambers relax and fill again.
- Heartbeat
- One cycle of contraction and relaxation that moves blood through the heart.
- Septum
- The wall separating the left and right sides of the heart.
- Coronary veins
- Vessels draining blood from the heart muscle towards the right atrium.
- Coronary arteries
- Arteries supplying oxygen and nutrients to the heart muscle.
- Left atrium
- The chamber receiving oxygenated blood from the pulmonary veins.
- Left ventricle
- The chamber pumping oxygenated blood into the aorta.
- Pulmonary veins
- Vessels returning oxygenated blood from the lungs to the heart.
- Pulmonary arteries
- Vessels carrying deoxygenated blood from the heart to the lungs.
- Inferior vena cava
- The large vein returning blood from the lower body to the right atrium.
- Right atrium
- The chamber receiving deoxygenated blood from the venae cavae.
- Right ventricle
- The chamber pumping blood towards the lungs.