The cardiovascular system transports blood throughout the body. The heartbeat pushes oxygen-rich blood from the lungs through the arteries and into organs and tissues throughout the body. Organs and tissues use the oxygen in the blood in order to function and release carbon dioxide as waste. The blood then moves through the veins to the lungs. The lungs exchange the carbon dioxide in the blood for oxygen, and the blood moves back into the heart to repeat the cycle.
The blood is the key component of the cardiovascular system--all of the other parts of the system move the blood where it is needed. The two portions of the blood are plasma, which is a clear liquid, and a "formed elements" portion, which is made of cells and cell parts.
The heart beats to pump the blood through the body and can adjust the rate and force of its beating when body tissues need more oxygen, such as beating faster during exercise because the muscles need more oxygen and energy.
The blood leaves the heart through the aorta, which is the largest artery. The arteries carry oxygenated blood from the heart to the capillaries, tiny blood vessels in body tissues. Red blood cells within the capillaries deliver oxygen to the body's cells and remove carbon dioxide. Then veins carry the blood back to the lungs.
The blood has three main functions: transportation, regulation and protection. Red blood cells deliver oxygen from the lungs to other cells for metabolism and nutrients from the digestive tract to feed the cells. The blood also transports waste products to locations where the body can excrete them. Blood regulates the body's levels of pH, temperature and cell water content. It protects the body by clotting to minimise blood loss and by carrying immune cells.
The heart consists of four chambers. The heart's left atrium receives oxygen-rich blood from the lungs through the pulmonary veins. Blood travels through the bicuspid valve into the left ventricle, which is the largest and most powerful of the heart's chambers. The left ventricle pumps blood through the aortic valve into the aorta, and on to the rest of the body. Carbon dioxide-rich, oxygen-poor blood enters the heart's right atrium from the superior vena cava, inferior vena cava, and coronary sinus. The right atrium pumps the blood through the tricuspid valve into the right ventricle, which pumps the blood through the pulmonary valve to the pulmonary trunk and pulmonary arteries and into the lungs.
The deadliest disorders of the cardiovascular system are heart disease and stroke. According to the Centers for Disease Control and Prevention (CDC), heart disease is the leading cause of death in the United States, and stroke is the third-leading cause of death. Some people are born with cardiovascular problems, while other cases of disease develop over time.
Arteriosclerosis, or hardening of the arteries, is a common type of cardiovascular disease that can occur when atherosclerotic plaques form in the walls of the arteries, causing them to thicken and lose their elasticity. These plaques are formed when LDL, or "bad cholesterol," accumulates within the walls of an artery. Atherosclerotic plaques can then break open and trigger blood clots to form, which can block the blood flow through the artery and starve the tissue of oxygen. If total blockage of an artery occurs in the brain, causing brain tissue death, it is a stroke, or "cerebrovascular accident." If a total blockage occurs in the coronary arteries, causing heart muscle death, it is a heart attack, also known as a "myocardial infarction" or "MI." A partial blockage of blood flow to the heart causes myocardial ischemia, which weakens heart cells and is usually accompanied by angina pectoris. People often describe angina pectoris as a severe pain in the chest, along with a feeling of tightness. The pain may radiate to the neck or chin, or down the left arm.
Strokes can be caused by a blocked artery in the brain, as described above, or by bleeding in the brain. Brain tissue damage caused by bleeding in the brain is called a hemorrhagic stroke. Symptoms of a stroke can include the sudden onset of neurologic symptoms such as numbness, paralysis, or difficulty speaking.
The American Heart Association says that warning signs of a heart attack can include lasting or recurring "pressure, squeezing fullness or pain" in the chest or in other parts of the upper body, such as the jaw, arm, back, neck or stomach. Shortness of breath, nausea, cold sweats or lightheadedness can also be symptoms of a heart attack. The American Heart Association urges anyone who is unsure whether or not she is having a heart attack to call 911 immediately.
The American Heart Association says that possible signs of a stroke include sudden onset of numbness, tingling, confusion, trouble walking, trouble speaking or understanding, loss of balance, trouble seeing, or severe and unexplained headache. As with heart attack, AHA recommends that anyone who thinks he may be having a stroke should call 911 immediately. Immediate treatment is extremely important in cases of heart attack or stroke.
The CDC recommends the following steps to help prevent heart disease and stroke: prevent and control high blood pressure (hypertension); prevent and control diabetes; avoid tobacco; moderate alcohol use; maintain a healthy weight; regular physical activity; and practice good nutrition.