Heart Anatomy

Anatomy of the Heart Your heart is located under the ribcage in the center of your chest between your right and left lungs. Its muscular walls beat, or contract, pumping blood continuously to all parts of your body. The size of your heart can vary depending on your age, size, and the condition of your heart. A normal, healthy, adult heart most often is the size of an average clenched adult fist. Some diseases of the heart can cause it to become larger. The Exterior of the Heart Below is a picture of the outside of a normal, healthy, human heart. Heart Exterior   The illustration shows the front surface of a heart, including the coronary arteries and major blood vessels. The heart is the muscle in the lower half of the picture. The heart has four chambers. The right and left atria (AY-tree-uh) are shown in purple. The right and left ventricles (VEN-trih-kuls) are shown in red. Some of the main blood vessels—arteries and veins—that make up your blood circulatory system are directly connected to the heart. The ventricle on the right side of your heart pumps blood from your heart to your lungs. When you breathe air in, oxygen passes from your lungs through your blood vessels and into your blood. Carbon dioxide, a waste product, is passed from your blood through blood vessels to your lungs and is removed from your body when you breathe out. The left atrium receives oxygen-rich blood from your lungs. The pumping action of your left ventricle sends this oxygen-rich blood through the aorta (a main artery) to the rest of your body. The Right Side of Your Heart The superior and inferior vena cavae are in blue to the left of the heart muscle as you look at the picture. These veins are the largest veins in your body. After your body's organs and tissues have used the oxygen in your blood, the vena cavae carry the oxygen-poor blood back to the right atrium of your heart. The superior vena cava carries oxygen-poor blood from the upper parts of your body, including your head, chest, arms, and neck. The inferior vena cava carries oxygen-poor blood from the lower parts of your body. The oxygen-poor blood from the vena cavae flows into your heart's right atrium and then on to the right ventricle. From the right ventricle, the blood is pumped through the pulmonary (PULL-mun-ary) arteries (in blue in the center of the picture) to your lungs. There, through many small, thin blood vessels called capillaries, the blood picks up more oxygen. The oxygen-rich blood passes from your lungs back to your heart through the pulmonary veins (in red to the left of the right atrium in the picture). The Left Side of Your Heart Oxygen-rich blood from your lungs passes through the pulmonary veins (in red to the right of the left atrium in the picture). It enters the left atrium and is pumped into the left ventricle. From the left ventricle, the oxygen-rich blood is pumped to the rest of your body through the aorta. Like all of your organs, your heart needs blood rich with oxygen. This oxygen is supplied through the coronary arteries as blood is pumped out of your heart's left ventricle. Your coronary arteries are located on your heart's surface at the beginning of the aorta. Your coronary arteries (shown in red in the drawing) carry oxygen-rich blood to all parts of your heart. The Interior of the Heart Below is a picture of the inside of a normal, healthy, human heart. Heart Interior The illustration shows a cross-section of a healthy heart and its inside structures. The blue arrow shows the direction in which oxygen-poor blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body. The Septum The right and left sides of your heart are divided by an internal wall of tissue called the septum. The area of the septum that divides the atria (the two upper chambers of your heart) is called the atrial or interatrial septum. The area of the septum that divides the ventricles (the two lower chambers of your heart) is called the ventricular or interventricular septum. Heart Chambers The picture shows the inside of your heart and how it's divided into four chambers. The two upper chambers of your heart are called atria. The atria receive and collect blood. The two lower chambers of your heart are called ventricles. The ventricles pump blood out of your heart into the circulatory system to other parts of your body. Heart Valves The picture shows your heart's four valves. Shown counterclockwise in the picture, the valves include the aortic (ay-OR-tik) valve, the tricuspid (tri-CUSS-pid) valve, the pulmonary valve, and the mitral (MI-trul) valve. Blood Flow The arrows in the drawing show the direction that blood flows through your heart. The light blue arrows show that blood enters the right atrium of your heart from the superior and inferior vena cavae. From the right atrium, blood is pumped into the right ventricle. From the right ventricle, blood is pumped to your lungs through the pulmonary arteries. The light red arrows show the oxygen-rich blood coming in from your lungs through the pulmonary veins into your heart's left atrium. From the left atrium, the blood is pumped into the left ventricle. The left ventricle pumps the blood to the rest of your body through the aorta. For the heart to work properly, your blood must flow in only one direction. Your heart's valves make this possible. Both of your heart's ventricles have an "in" (inlet) valve from the atria and an "out" (outlet) valve leading to your arteries. Healthy valves open and close in very exact coordination with the pumping action of your heart's atria and ventricles. Each valve has a set of flaps called leaflets or cusps that seal or open the valves. This allows pumped blood to pass through the chambers and into your arteries without backing up or flowing backward.

Blood Circulation

Systemic circulation is the portion of the cardiovascular system which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart. The term is contrasted with pulmonary circulation

Course

In the systemic circulation, arteries bring oxygenated blood to the tissues. As blood circulates through the body, oxygen diffuses from the blood into cells surrounding the capillaries, and carbon dioxide diffuses into the blood from the capillary cells. Veins bring deoxygenated blood back to the heart.

Arteries

Oxygenated blood enters the systemic circulation when leaving the left ventricle, through the aortic semilunar valve. The first part of the systemic circulation is the artery aorta, a massive and thick-walled artery. The aorta arches and gives off major arteries to the upper body before piercing the diaphragm in order to supply the lower parts of the body with its various branches.

Capillaries

Blood passes from arteries to arterioles and finally to capillaries, which are the thinnest and most numerous of the blood vessels. These capillaries help to join tissue with arterioles for transportation of nutrition to the cells, which absorb oxygen and nutrients in the blood. Peripheral tissues do not fully deoxygenate the blood, so venous blood does have oxygen, but in a lower concentration than in arterial blood. In addition, carbon dioxide and wastes are added. The capillaries can only fit one cell at a time.

Venules

The deoxygenated blood is then collected by venules, from where it flows first into veins, and then into the inferior and superior venae cavae, which return it to the right heart, completing the systemic cycle. The blood is then re-oxygenated through the pulmonary circulation before returning again to the systemic circulation.

Veins

The relatively deoxygenated blood collects in the venous system which coalesces into two major veins: the superior vena cava (roughly speaking from areas above the heart) and the inferior vena cava (roughly speaking from areas below the heart). These two great vessels exit the systemic circulation by emptying into the right atrium of the heart. The coronary sinus empties the heart's veins themselves into the right atrium.