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Heart and Circulatory System
With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to all of our cells. Each day, 2,000 gallons (more than 7,570 liters) of blood travel many times through about 60,000 miles (96,560 kilometers) of blood vessels that branch and cross, linking the cells of our organs and body parts. From the hard-working heart to our thickest arteries to capillaries so thin that they can only be seen through a microscope, the heart and circulatory system (also called the cardiovascular system) is our body's lifeline, delivering blood to the body's tissues.
What Is the Heart and Circulatory System?
The circulatory system is composed of the heart and blood vessels, including arteries, veins, and capillaries. Our bodies actually have two circulatory systems: The pulmonary circulation is a short loop from the heart to the blood from the heart to all the other parts of our bodies and back again.
The heart is the key organ in the circulatory system. As a hollow, muscular pump, its main function is to propel blood throughout the body. It usually beats from 60 to 100 times per minute, but can go much faster when necessary. It beats about 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime.
The heart gets messages from the body that tell it when to pump more or less blood depending on an individual's needs. When we're sleeping, it pumps just enough to provide for the lower amounts of oxygen needed by our bodies at rest. When we're exercising or frightened, the heart pumps faster to increase the delivery of oxygen.
The heart has four chambers that are enclosed by thick, muscular walls. It lies between the lungs and just to the left of the middle of the chest cavity. The bottom part of the heart is divided into two chambers called the right and left ventricles, which pump blood out of the heart. A wall called the interventricular septum divides the ventricles.
The upper part of the heart is made up of the other two chambers of the heart, called the right and left atria. The right and left atria receive the blood entering the heart. A wall called the interatrial septum divides the right and left atria, which are separated from the ventricles by the atrioventricular valves. The tricuspid valve separates the right atrium from the right ventricle, and the mitral valve separates the left atrium and the left ventricle.
Two other cardiac valves separate the ventricles and the large blood vessels that carry blood leaving the heart. These valves are called the pulmonic valve, which separates the right ventricle from the pulmonary artery leading to the lungs, and the aortic valve, which separates the left ventricle from the aorta, the body's largest blood vessel.
Blood vessels carrying blood away from the heart are called arteries. They are the thickest blood vessels, with muscular walls that contract to keep the blood moving away from the heart and through the body. In the systemic circulation, oxygen-rich blood is pumped from the heart into the aorta. This huge artery curves up and back from the left ventricle, then heads down in front of the spinal column into the abdomen. Two coronary arteries branch off at the beginning of the aorta and divide into a network of smaller arteries that provide oxygen and nourishment to the muscles of the heart.
Unlike the aorta, the body's other main artery, the pulmonary artery, carries oxygen-poor blood. From the right ventricle, the pulmonary artery divides into right and left branches, on the way to the lungs where blood picks up oxygen.
Arterial walls have three layers:
- The endothelium is on the inside and provides a smooth lining for blood to flow over as it moves through the artery.
- The media is the middle part of the artery, made up of a layer of muscle and elastic tissue.
- The adventitia is the tough covering that protects the outside of the artery.
As they get farther from the heart, the arteries branch out into arterioles, which are smaller and less elastic.
Blood vessels that carry blood back to the heart are called veins. They're not as muscular as arteries, but they contain valves that prevent blood from flowing backward. Veins have the same three layers that arteries do, but are thinner and less flexible. The two largest veins are the superior and inferior vena cavae. The terms superior and inferior don't mean that one vein is better than the other, but that they're located above and below the heart.
A network of tiny capillaries connects the arteries and veins. Though tiny, the capillaries are one of the most important parts of the circulatory system because it's through them that nutrients and oxygen are delivered to the cells. In addition, waste products such as carbon dioxide are also removed by the capillaries.
What Does the Heart and Circulatory System Do?
The circulatory system works closely with other systems in our bodies. It supplies oxygen and nutrients to our bodies by working with the respiratory system. At the same time, the circulatory system helps carry waste and carbon dioxide out of the body. Hormones - produced by the Congenital heart defects are abnormalities in the heart's structure that are present at birth. Out of every 1,000 live births, there are approximately eight newborns who have congenital heart defects ranging from mild to severe. Congenital heart defects occur while the fetus is developing in the mother's uterus and it's not usually known why they occur. Some congenital heart defects are caused by genetic disorders, but most are not. What all congenital heart murmur. A heart murmur is an abnormal sound (like a blowing or whooshing sound) that's heard when listening to the heart. Usually a heart murmur is detected by a doctor who's listening to the heart with a stethoscope during a routine exam. Murmurs are very common in children and can be caused by congenital heart defects or other heart conditions.
Arrhythmia. Cardiac arrhythmias, which are also called dysrhythmias or rhythm disorders, are abnormalities in the heart's rhythm. Arrhythmias may be caused by a congenital heart defect or they may be acquired later. An arrhythmia may cause the heart's rhythm to be irregular, abnormally fast, or abnormally slow. Arrhythmias can occur at any age and may be discovered during a routine physical examination. Depending on the type of rhythm disorder a person has, arrhythmias may be treated with medication, surgery, or pacemakers.
Cardiomyopathy. Cardiomyopathy is a chronic disease that causes the heart muscle (the myocardium) to become weakened. Usually, the disease first affects the lower chambers of the heart, the ventricles, and then progresses and damages the muscle cells and even the tissues surrounding the heart. In its most severe forms, this condition may lead to heart failure and even death. Cardiomyopathy is the number-one reason for heart transplants in children.
Coronary artery disease. The most common heart disorder in adults, coronary artery disease is caused by atherosclerosis. Deposits of fat, calcium, and dead cells, called atherosclerotic plaques, form on the inner walls of the coronary arteries (the blood vessels that supply the heart) and interfere with the smooth flow of blood. Blood flow to the heart muscle may even stop if a thrombus, or clot, forms in a coronary vessel, which may cause a heart attack. In a heart attack (also known as a myocardial infarction), the heart muscle becomes damaged by lack of oxygen, and unless blood flow returns within minutes, muscle damage increases, and the heart's ability to pump blood is compromised. If the clot can be dissolved within a few hours, damage to the heart can be reduced. Heart attacks are rare in children and teens.
Hyperlipidemia/hypercholesterolemia (high cholesterol). Cholesterol is a waxy substance that's found in the body's cells, in the blood, and in some of the foods we eat. Having too much cholesterol in the blood, also known as hypercholesterolemia or hyperlipidemia, is a major risk factor for heart disease and can lead to a heart attack.
Cholesterol is carried in the bloodstream by lipoproteins. Two kinds - low-density lipoproteins (LDL) and high-density lipoproteins (HDL) - are the most important. High levels of LDL cholesterol (the bad cholesterol) increase a person's risk for heart disease and stroke, whereas high levels of HDL cholesterol (the good cholesterol) can protect against these.
A blood test can indicate if a person's cholesterol is too high. A child's cholesterol level is borderline if it's 170 to 199 mg/dL, and it's considered high if it's above 200 mg/dL.
About 10% of teens between 12 and 19 have high cholesterol levels that put them at increased risk of cardiovascular disease.
Kawasaki disease. Kawasaki disease (also known as mucocutaneous lymph node syndrome) affects the mucous membranes (the lining of the mouth and breathing passages), the skin, and the lymph nodes (part of the immune system). Kawasaki disease can also lead to vasculitis, which is an inflammation of the blood vessels. This can affect all major arteries in the body - including the coronary arteries, which supply blood to the heart. It can also cause inflammation of the heart muscle, a condition called myocarditis. When coronary arteries become inflamed, a child can develop aneurysms, which are weakened and bulging spots on the walls of arteries. This increases the risk of a blood clot forming in this weakened area, which can block the artery, possibly leading to a heart attack. In addition to the coronary arteries, the heart muscle, lining, valves, or the outer membrane that surrounds the heart can become inflamed. Arrhythmias (changes in the normal pattern of the heartbeat) or abnormal functioning of some heart valves can occur. Kawasaki disease has surpassed rheumatic fever as the leading cause of acquired heart disease in children in the United States.
Rheumatic heart disease. Usually the complication of an untreated exercise, eating a weight, and getting regular Steven Dowshen, MD
Date reviewed: July 2007