Circulatory system
IntroductionSystemic Circulation – delivers blood to all body cells and carries away wastePulmonary Circulation – eliminates carbon dioxide and oxygenates blood (lung pathway)Arteries - carry blood away from the heart Veins - return blood to the heartStructure of the HeartHeart Size – about 14 cm x 9 cm (the size of a fist)Coverings of the heartPericardium encloses the heart (like a bag) (visceral, parietal)Pericardial cavity – contains fluid for the heart to float in, reducing frictionWall of the HeartEpicardium – outer layer, reduces frictionMyocardium – middle layer, mostly cardiac muscleEndocardium – inner layer, blood vessels and Purkinje fibers
Heart Chambers and Valves
Atria - top chambers
Ventricles - bottom chambers
Septum - divides left and right side
Atrioventricular Valve (AV) - these valves are located between the atrium and the ventricle
Tricuspid - right side AV
Bicuspid - left side AV, also called mitral valve
Superior Vena Cava - vessel the returns blood to the heart from the upper body
Inferior Vena Cava - vessel the returns blood to the heart from the lower body
Coronary Sinus - indentation on the front of the heart
Chordae tendinae / Papillary Muscles - muscles and tendons that hold the heart valves in place
Pulmonary Trunk/Arteries - large vessel that splits into the left and right pulmonary arteries, these are the only arteries that carry deoxygenated blood
Pulmonary valve - controls the flow of blood into the pulmonary trunk
Pulmonary Veins - returns oxygenated blood from the lungs
Aorta - large vessel that delivers blood to the body
Aortic Valve - controls the flow of blood into the aorta
Path of Blood Through the Heart
Quick Overview
1. Deoxygenated blood enters right atrium through the vena cava
2. Blood moves into the right ventricle
3. Blood goes out the pulmonary arteries and heads to the lungs
4. Blood returns from the lungs and enters the left atrium
5. Blood moves into the left ventricle
6. Oxygenated blood moves out of the left ventricle through the aorta and to the body
Labeling Practice - External Heart
See Also: Labeling Internal Heart
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.
Heart Exterior
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 above, the superior and inferior venacavae, to the left of the heart muscle as you look at the picture, 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 Topics How the Lungs Work article.
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.
Heart Interior
Heart Chambers
Figure above 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.
The Septum
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.
Heart Valves
Figure above 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 figure above show the direction that blood flows through your heart. The 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 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.