Human Heart, Front View
Image Caption : Heart, Front View : Because every cell in the body must have a never-ending supply of oxygenated blood, the heart never stops beating throughout a person's lifetime. It beats about 100,000 times a day, pumping 6 quarts of blood through the 65,000 miles of vessels that comprise the adult circulatory system, three times every minute.
Anatomy of the Heart
Your heart is located under your ribcage in the center of your chest between your right and left lungs. Its muscular walls beat, or contract, pumping blood 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 usually is the size of an average clenched adult fist. Some diseases can cause the heart to enlarge.
The Exterior of the Heart
Below is a picture of the outside of a normal, healthy, human heart.
In figure B, the heart is the muscle in the lower half of the picture. The heart has four chambers. The heart's upper chambers, the right and left atria (AY-tree-uh), are shown in purple. The heart's lower chambers, 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 circulatory system are directly connected to the heart.
THE RIGHT SIDE OF YOUR HEART
In figure B above, the superior and inferior vena cavae are shown 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 to the right ventricle. From the right ventricle, the blood is pumped through the pulmonary (PULL-mun-ary) arteries (shown in blue in the center of figure B) to your lungs.
Once in the lungs, the blood travels through many small, thin blood vessels called capillaries. There, the blood picks up more oxygen and transfers carbon dioxide to the lungs—a process called gas exchange. To learn more about gas exchange, go to the Health TopicsHow the Lungs Workarticle.
The oxygen-rich blood passes from your lungs back to your heart through the pulmonary veins (shown in red to the left of the right atrium in figure B).
THE LEFT SIDE OF YOUR HEART
Oxygen-rich blood from your lungs passes through the pulmonary veins (shown in red to the right of the left atrium in figure B above). The blood 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. The aorta is the main artery that carries oxygen-rich blood to your body.
Like all of your organs, your heart needs oxygen-rich blood. As blood is pumped out of your heart's left ventricle, some of it flows into the coronary arteries (shown in red in figure B).
Your coronary arteries are located on your heart's surface at the beginning of the aorta. They 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.
Figure B shows the inside of your heart and how it's divided into four chambers. The two upper chambers of your heart are called the atria. They receive and collect blood.
The two lower chambers of your heart are called ventricles. The ventricles pump blood out of your heart to other parts of your body.
An internal wall of tissue divides the right and left sides of your heart. This wall is called the septum.
The area of the septum that divides the atria is called the atrial or interatrial septum. The area of the septum that divides the ventricles is called the ventricular or interventricular septum.
Figure B 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.
The arrows in figure B show the direction that blood flows through your heart. The light blue arrow shows 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 arrow shows oxygen-rich blood coming 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 well, 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 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 valve. This allows blood to pass through the chambers and into your arteries without backing up or flowing backward.
What Is the Heart?
Your heart is a muscular organ that pumps blood to your body. Your heart is at the center of your circulatory system. This system consists of a network of blood vessels, such as arteries, veins, and capillaries. These blood vessels carry blood to and from all areas of your body.
An electrical system controls your heart and uses electrical signals to contract the heart's walls. When the walls contract, blood is pumped into your circulatory system. Inlet and outlet valves in your heart chambers ensure that blood flows in the right direction.
Your heart is vital to your health and nearly everything that goes on in your body. Without the heart's pumping action, blood can't move throughout your body.
Your blood carries the oxygen and nutrients that your organs need to work well. Blood also carries carbon dioxide (a waste product) to your lungs so you can breathe it out.
A healthy heart supplies your body with the right amount of blood at the rate needed to work well. If disease or injury weakens your heart, your body's organs won't receive enough blood to work normally.
National Heart Lung and Blood Institute / NIH
STRUCTURE OF THE HEART
The human heart is a four-chambered muscular organ, shaped and sized roughly like a man's closed fist with two-thirds of the mass to the left of midline.
The heart is enclosed in a pericardial sac that is lined with the parietal layers of a serous membrane. The visceral layer of the serous membrane forms the epicardium.
LAYERS OF THE HEART WALL
Three layers of tissue form the heart wall. The outer layer of the heart wall is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium.
CHAMBERS OF THE HEART
The internal cavity of the heart is divided into four chambers:
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
The two atria are thin-walled chambers that receive blood from the veins. The two ventricles are thick-walled chambers that forcefully pump blood out of the heart. Differences in thickness of the heart chamber walls are due to variations in the amount of myocardium present, which reflects the amount of force each chamber is required to generate.
The right atrium receives deoxygenated blood from systemic veins; the left atrium receives oxygenated blood from the pulmonary veins.
VALVES OF THE HEART
Pumps need a set of valves to keep the fluid flowing in one direction and the heart is no exception. The heart has two types of valves that keep the blood flowing in the correct direction. The valves between the atria and ventricles are called atrioventricular valves (also called cuspid valves), while those at the bases of the large vessels leaving the ventricles are called semilunar valves.
The right atrioventricular valve is the tricuspid valve. The left atrioventricular valve is the bicuspid, or mitral, valve. The valve between the right ventricle and pulmonary trunk is the pulmonary semilunar valve. The valve between the left ventricle and the aorta is the aortic semilunar valve.
When the ventricles contract, atrioventricular valves close to prevent blood from flowing back into the atria. When the ventricles relax, semilunar valves close to prevent blood from flowing back into the ventricles.
PATHWAY OF BLOOD THROUGH THE HEART
While it is convenient to describe the flow of blood through the right side of the heart and then through the left side, it is important to realize that both atria and ventricles contract at the same time. The heart works as two pumps, one on the right and one on the left, working simultaneously. Blood flows from the right atrium to the right ventricle, and then is pumped to the lungs to receive oxygen. From the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped to the systemic circulation.
BLOOD SUPPLY TO THE MYOCARDIUM
The myocardium of the heart wall is a working muscle that needs a continuous supply of oxygen and nutrients to function efficiently. For this reason, cardiac muscle has an extensive network of blood vessels to bring oxygen to the contracting cells and to remove waste products.
The right and left coronary arteries, branches of the ascending aorta, supply blood to the walls of the myocardium. After blood passes through the capillaries in the myocardium, it enters a system of cardiac (coronary) veins. Most of the cardiac veins drain into the coronary sinus, which opens into the right atrium.
National Cancer Institute / NIH
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