The heart’s electrical system
To pump blood throughout the body, the muscles of the heart must work together to squeeze the blood in the right direction, at the right time, and with the right force. Electrical impulses coordinate this activity.
The electrical signal begins at the sino-atrial node, sometimes called the sinus, or SA, node. This is the heart’s pacemaker, and it sits at the top of the right atrium. The signal causes the atria to contract, pushing blood down into the ventricles.
The electrical impulse then travels to an area of cells at the bottom of the right atrium, between the atria and ventricles, called the atrioventricular, or AV, node.
These cells act as a gatekeeper. They coordinate the signal so that the atria and ventricles do not contract at the same time. There needs to be a slight delay.
From here, the signal travels along fibers, called Purkinje fibers, within the ventricle walls. The fibers pass the impulse to the heart muscle, causing the ventricles to contract.
There are three types of blood vessels:
Arteries: These carry oxygenated blood from the heart to the rest of the body. The arteries are strong, muscular, and stretchy, which helps push blood through the circulatory system, and they also help regulate blood pressure. The arteries branch into smaller vessels called arterioles.
Veins: These carry deoxygenated blood back to the heart, and they increase in size as they get closer to the heart. Veins have thinner walls than arteries.
Capillaries: These connect the smallest arteries to the smallest veins. They have very thin walls, which allow them to exchange compounds such as carbon dioxide, water, oxygen, waste, and nutrients with surrounding tissues.
The heart, blood, and blood vessels make up the circulatory, or cardiovascular, system.
Here, learn about some diseases that can affect this system.
The heart is essential to life — if it stops beating, blood will not reach the brain and other organs, and the person can die
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