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Circulatory System: Facts, Function & Diseases

The circulatory system is a vast network of organs and vessels that is responsible for the flow of blood, nutrients, oxygen and other gases, and hormones to and from cells. Without the circulatory system, the body would not be able to fight disease or maintain a stable internal environment — such as proper temperature and pH — known as homeostasis.

Description of the circulatory system

While many view the circulatory system as simply a highway for blood — it is also known as the cardiovascular system — it is made up of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary) and arteries, veins, coronary and portal vessels (systemic).

In the average human, about 2,000 gallons (7,572 liters) of blood travel daily through about 60,000 miles (96,560 kilometers) of blood vessels. An average adult has 5 to 6 quarts (4.7 to 5.6 liters) of blood, which is made up of plasma, red blood cells, white blood cells and platelets. In addition to blood, the circulatory system moves lymph, which is a clear fluid that helps rid the body of unwanted material.

The heart, blood, and blood vessels make up the cardiovascular component of the circulatory system. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated. It also incorporates the systemic circulation, which runs through the rest of the body to provide oxygenated blood.

[Top 10 Amazing Facts About Your Heart]

The pulmonary circulatory system sends oxygen-depleted blood away from the heart through the pulmonary artery to the lungs and returns oxygenated blood to the heart through the pulmonary vein.

Oxygen-deprived blood enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle. From there it is pumped through the pulmonary semilunar valve into the pulmonary artery on its way to the lungs. When it gets to the lungs, carbon dioxide is released from the blood and oxygen is absorbed. The pulmonary vein sends the oxygen-rich blood back to the heart.

The systemic circulation is the portion of the circulatory system is the network of veins, arteries and blood vessels that transports blood from heart, services the body's cells and then re-enters the heart.

Infographic: Find out all about the blood, lungs and blood vessels that make up the circulatory system.

Diseases of the circulatory system

According to the American Heart Association, cardiovascular disease is the leading cause of death in the United States. Because of its vastness and critical nature, it is one of the systems of the body most prone to disease.

Credit: Blood pressure check photo via Shutterstock

One of the most common diseases of the circulatory system is arteriosclerosis, in which the fatty deposits in the arteries causes the walls to stiffen and thicken the walls. The causes are too much fat, cholesterol and calcium. This can restrict blood flow or in severe cases stop it all together, resulting in a heart attack or stroke.

Another circulatory is disease, hypertension — commonly called high blood pressure — causes the heart to work harder and can lead to such complications as a heart attack, a stroke, or kidney failure.

An aortic aneurysm occurs when the aorta is damaged and starts to bulge or eventually tear, which can cause severe internal bleeding. This weakness can be present at birth or the result of atherosclerosis, obesity, high blood pressure or a combination of these conditions.

 

Other disorders of the circulatory system result from damage or birth defects. Rheumatic fever can attack the valves that control the flow of blood through the heart. Incomplete development of the heart or blood vessels before birth may result in defects known as congenital heart disorders. [Erectile Dysfunction Linked to Cardiovascular Disease]

Study of the circulatory system

Cardiologists are specialists who are certified to diagnose, treat and prevent disease of the heart, arteries and veins. Cardiologists are certified by the American Board of Internal Medicine (ABIM) after meeting educational and practice requirements. Before being certified as cardiologists, those aspiring to the specialty must be certified in internal medicine. Then cardiologists can become certified in one of several cardiology subspecialties, including transplant cardiology, cardiovascular disease, clinical cardiac electrophysiology and interventional cardiology.

A common piece of medical equipment used to evaluate the circulatory system is the electrocardiogram. Also called an EKG or ECG, it measures how fast the heart is beating, whether the rhythm of the heartbeat is steady or irregular, and the strength and timing of electrical signals as they pass through each part of the heart.

Sphygmomanometers and stethoscopes are used to measure blood pressure and a pulse meter can monitor heart rate, rhythm and dropped beats.

Ready for Med School? Test Your Body Smarts
You use your eyes to see, your ears to hear and your muscles to do the heavy lifting. Well, sort of. In fact, most body parts are far more complicated than that, while some seem to have no business being inside there at all.
Find out how much you know about the body's parts and what they do (or don't do).
Start the Quiz
An illustration showing the different systems of the human body.
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Ready for Med School? Test Your Body Smarts
You use your eyes to see, your ears to hear and your muscles to do the heavy lifting. Well, sort of. In fact, most body parts are far more complicated than that, while some seem to have no business being inside there at all.
Find out how much you know about the body's parts and what they do (or don't do).
Start Quiz
An illustration showing the different systems of the human body.
0 of questions complete

Milestones

Some milestones in the history and study of the circulatory system include:

  • 16th century B.C.: The Ebers Papyrus, an ancient Egyptian medical document, provides some of the earliest writing on the circulatory. It describes the connection of the heart to the arteries.
  • 6th century B.C.: Ayurvedic physician Sushruta in ancient India describes how vital fluids circulate through the body.
  • 2nd century A.D.: the Greek physician Galen documents how blood vessels carry blood, identifies venous (dark red) and arterial (brighter and thinner) blood and notes that each has a separate functions.
  • 1628: William Harvey, an English physician, first describes blood circulation.
  • 1706: Raymond de Vieussens, a French anatomy professor, first describes the structure of the heart's chambers and vessels.
  • 1733: Stephen Hales, an English clergyman and scientist, measures blood pressure for the first time.
  • 1816: Rene T.H. Laennec, a French physician, invents the stethoscope.
  • 1902: American physician James B. Herrick first documents heart disease resulting from hardening of the arteries.
  • 1903: Dutch physiologist Willem Einthoven invents the electrocardiograph.
  • 1952: The first successful open heart surgery takes place by F. John Lewis, an American surgeon.
  • 1967: South African surgeon Christiaan Barnard performs the first transplant of a whole heart from one person to another.
  • 1982: American physician Robert Jarvik designs the first artificial heart and American surgeon Willem DeVries implants it.

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