Your heart and blood vessels make up your overall blood circulatory system. Your blood circulatory system is made up of four subsystems.
Arterial circulation is the part of your circulatory system that involves arteries, like the aorta and pulmonary arteries. Arteries are blood vessels that carry blood away from your heart. (The exception is the coronary arteries, which supply your heart muscle with oxygen-rich blood.)
Healthy arteries are strong and elastic (stretchy). They become narrow between heartbeats, and they help keep your blood pressure consistent. This helps blood move through your body.
Arteries branch into smaller blood vessels called arterioles (ar-TEER-e-ols). Arteries and arterioles have strong, flexible walls that allow them to adjust the amount and rate of blood flowing to parts of your body.
Venous circulation is the part of your circulatory system that involves veins, like the vena cavae and pulmonary veins. Veins are blood vessels that carry blood to your heart.
Veins have thinner walls than arteries. Veins can widen as the amount of blood passing through them increases.
Capillary circulation is the part of your circulatory system where oxygen, nutrients, and waste pass between your blood and parts of your body.
Capillaries are very small blood vessels. They connect the arterial and venous circulatory subsystems.
The importance of capillaries lies in their very thin walls. Oxygen and nutrients in your blood can pass through the walls of the capillaries to the parts of your body that need them to work normally.
Capillaries’ thin walls also allow waste products like carbon dioxide to pass from your body’s organs and tissues into the blood, where it’s taken away to your lungs.
Pulmonary circulation is the movement of blood from the heart to the lungs and back to the heart again. Pulmonary circulation includes both arterial and venous circulation.
Oxygen-poor blood is pumped to the lungs from the heart (arterial circulation). Oxygen-rich blood moves from the lungs to the heart through the pulmonary veins (venous circulation).
Pulmonary circulation also includes capillary circulation. Oxygen you breathe in from the air passes through your lungs into your blood through the many capillaries in the lungs. Oxygen-rich blood moves through your pulmonary veins to the left side of your heart and out of the aorta to the rest of your body.
Capillaries in the lungs also remove carbon dioxide from your blood so that your lungs can breathe the carbon dioxide out into the air.
Your Heart’s Electrical System
Your heart’s electrical system controls all the events that occur when your heart pumps blood. The electrical system also is called the cardiac conduction system. If you’ve ever seen the heart test called an EKG (electrocardiogram), you’ve seen a graphical picture of the heart’s electrical activity.
Your heart’s electrical system is made up of three main parts:
- The sinoatrial (SA) node, located in the right atrium of your heart
- The atrioventricular (AV) node, located on the interatrial septum close to the tricuspid valve
- The His-Purkinje system, located along the walls of your heart’s ventricles
A heartbeat is a complex series of events. These events take place inside and around your heart. A heartbeat is a single cycle in which your heart’s chambers relax and contract to pump blood. This cycle includes the opening and closing of the inlet and outlet valves of the right and left ventricles of your heart.
Each heartbeat has two basic parts: diastole and systole. During diastole, the atria and ventricles of your heart relax and begin to fill with blood.
At the end of diastole, your heart’s atria contract (atrial systole) and pump blood into the ventricles. The atria then begin to relax. Your heart’s ventricles then contract (ventricular systole), pumping blood out of your heart.
Each beat of your heart is set in motion by an electrical signal from within your heart muscle. In a normal, healthy heart, each beat begins with a signal from the SA node. This is why the SA node sometimes is called your heart’s natural pacemaker. Your pulse, or heart rate, is the number of signals the SA node produces per minute.
The signal is generated as the vena cavae fill your heart’s right atrium with blood from other parts of your body. The signal spreads across the cells of your heart’s right and left atria.
This signal causes the atria to contract. This action pushes blood through the open valves from the atria into both ventricles.
The signal arrives at the AV node near the ventricles. It slows for an instant to allow your heart’s right and left ventricles to fill with blood. The signal is released and moves along a pathway called the bundle of His, which is located in the walls of your heart’s ventricles.
From the bundle of His, the signal fibers divide into left and right bundle branches through the Purkinje fibers. These fibers connect directly to the cells in the walls of your heart’s left and right ventricles (see yellow on the picture in the animation).
The signal spreads across the cells of your ventricle walls, and both ventricles contract. However, this doesn’t happen at exactly the same moment.
The left ventricle contracts an instant before the right ventricle. This pushes blood through the pulmonary valve (for the right ventricle) to your lungs, and through the aortic valve (for the left ventricle) to the rest of your body.
As the signal passes, the walls of the ventricles relax and await the next signal.
This process continues over and over as the atria refill with blood and more electrical signals come from the SA node.
Your heart is made up of many parts working together to pump blood. In a healthy heart, all the parts work well so that your heart pumps blood normally. As a result, all parts of your body that depend on the heart to deliver blood also stay healthy.
Heart disease can disrupt a heart’s normal electrical system and pumping functions. Diseases and conditions of the heart’s muscle make it hard for your heart to properly pump blood.
Damaged or diseased blood vessels make the heart work harder than normal. Problems with the heart’s electrical system, called arrhythmias (ah-RITH-me-ahs), can make it hard for the heart to pump blood efficiently.