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About the Circulatory System
The circulatory system is an extensive and complex network of blood vessels and lymphatic vessels which supply the entire body with oxygen and nutrients. This system includes the lungs, heart, arteries, blood vessels, and capillaries. The average human body contains approximately five liters of blood, which is continually circulating from the heart to all other parts of the body, and back to the heart again.
As blood and lymph circulate around the body, oxygen and nutrients are delivered to tissues and organs, and waste products are absorbed for excretion. Waste gases, for example, are excreted during the exhalation phase of breathing. When blood passes through the kidneys, many other waste products are removed, some of which are excreted in urine. In the liver, sugars are removed from the blood and stored.
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Common Human Circulatory System Diseases
Human circulatory system diseases can be separated into several categories, including diseases of the heart, diseases of the vascular system, and diseases of the lymphatic system.
Heart disease is the number one killer in the United States, and is also a very significant cause of physical disability. Heart disease can take several different forms. The most common of these is coronary artery disease, in which the coronary artery that feeds the heart becomes narrowed or blocked. Coronary artery disease is the primary cause of heart attacks.
Another common type of heart disease is heart failure. This is typically the result of heart valve damage or malformation, or of physical factors that reduce the ability of the heart to pump blood effectively.
Vascular diseases are diseases of the arteries and veins that supply oxygen and nutrients to tissues and organs throughout the body. One of the most common vascular diseases is high blood pressure, or hypertension. This disease can have no identifiable cause, or can be caused by factors such as medication use. One important cause of hypertension is stenosis of the renal artery, in which the artery that feeds the kidneys becomes narrow or blocked.
Atherosclerosis, in which fatty deposits called plaques develop on artery walls, is most dangerous when it affects the coronary artery, as in coronary artery disease. Just as dangerous is carotid artery disease, where plaques narrow or block the carotid artery that supplies blood to the brain. A blockage in this artery can lead to a stroke.
Lymphatic diseases affect the lymphatic system, which includes the lymph nodes and lymph vessels. This network of tissues and vessels transports a fluid called lymph, which transports the white blood cells of the immune system around the body. This network helps fight infection by transporting white blood cells to locations in the body where they are needed. In addition, the lymphatic system helps circulate other body fluids, ensuring that the body does not retain more fluid than it needs.
Diseases of this system include infections, blockages in lymphatic vessels, and cancer. Specific diseases that can affect the lymphatic system include a cancer called lymphoma, and an autoimmune disease called lymphoproliferative syndrome.
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American Heart Association: Common Cardiovascular Diseases
National Institute of Health MedlinePlus: Heart Diseases
National Institute of Health MedlinePlus: Lymphatic Diseases
National Institute of Health MedlinePlus: Vascular Diseases
The Franklin Institute Resources for Science Learning: The Circulatory System