The cardiovascular system consists of a network of organs, including the heart and kidneys, which are connected by a vast conglomeration of blood vessels, mainly arteries, veins, and capillaries, through which blood flows in a closed system which never connects to the outside unless it is by means of trauma (injury) or deliberate surgery.
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The heart beats normally on a regular schedule, propelling the blood through the blood vessels to deliver oxygen and nutrients to all of the body’s tissues and organs and picking up wastes such as carbon dioxide which are produced by metabolism within the body. One of the organs that is serviced by the cardiovascular system is the heart itself.
For example, if it does not receive the oxygen supply that it needs because a coronary (heart) artery is clogged and blood flow is decreased, the heart muscle, which is called the myocardium, may become damaged. When it becomes partially starved of oxygen, we say that myocardial ischemia exists.
When it becomes completely deprived of oxygen, the heart muscle will die, and we say that myocardial infarction (a heart attack) has occurred. The same thing can happen to the brain, leading to a stroke, or the kidneys, causing renal insufficiency.
If the heart and blood vessels become overloaded with fluid, heart failure or high blood pressure (hypertension) may result. Of course, this is an oversimplification of what actually happens, but the main idea is that the cardiovascular system is very delicately balanced and if its function is disturbed, disease can occur.