Aneurysm is a balloon-like bulge that forms in a weakened area of the wall of an artery or vein. The most dangerous aneurysms are those that form in arteries, especially the arteries of the brain and the aorta. Most aneurysms result from atherosclerosis, a disease caused by cholesterol build-up in artery walls. Other causes of aneurysms include genetic disorders or other defects present at birth. The symptoms of an aneurysm vary with its location and size. There may be no symptoms, or pain may develop at the site of the aneurysm. Shortness of breath occurs if the aneurysm interferes with the heart's pumping ability. Some aneurysms press on nearby structures, producing a cough, hoarseness, or difficulty in swallowing. An aneurysm may worsen without the patient knowing and then suddenly rupture, causing a coma, paralysis, or death. Many strokes result from the rupture of an aneurysm in an artery of the brain.
Aneurysms can be detected with X-rays and, in many cases, can repair them surgically. Surgeons remove the diseased portion of the blood vessel. If it is a minor vessel, they tie off the loose ends. In a major artery or vein, they replace the diseased portion with a plastic tube, a fabric patch, or a piece of another blood vessel. Research Aneurysm
The aorta is the body's largest blood vessel. It arches out of the heart and down toward the lower body. It has a diameter of about one inch and blood rushes through it at a speed of about eight inches per second. The aorta is divided into several parts: the ascending aorta, the arch of the aorta, and the thoracic and abdominal portions of the descending aorta. Research Aorta
The aortic semilunar valve is situated at the beginning of the aorta. This valve has three delicate cusps, or pockets, which permitblood flow only in one direction, allowing blood to flow out of the left ventricle up into the aorta, but prevents backflow into the ventricle. When the heart refills, the crescent-shaped valve balloons out, sealed along the edge to prevent the blood from flowing backward. The blood's only exit from the ventricle is through the semilunar valves, so named for their crescent shaped cusps. Research Aortic Semilunar Valve
Arteries are muscular and elastic-walled vessels that form a network to carry oxygen-rich blood from the heart to all parts of the body. Smaller branches called arterioles extend from the arteries and connect to even smaller branches called metarterioles which deliver the blood to the capillaries. The exchange of oxygen and carbon dioxide between blood and body cells takes place through the thin walls of the capillaries.
There are two principal arteries or arterial trunks: the aorta, which rises from the left ventricle of the heart and ramifies through the whole body, sending off great branches to the head, neck, and upper limbs, and downwards to the lower limbs, etc; and the pulmonary artery, which conveys venous blood from the right ventricle to the lungs, to be purified in the process of respiration. Research Artery
Atherosclerosis is a form of arteriosclerosis. Atherosclerosis is the hardening of the arteries caused by cholesterol plaque deposits. It can occur in the coronary arteries, the carotid arteries, the aorta, and the leg arteries. Healthy arteries are flexible, strong, and elastic. The inner layer, the tunica interna, is smooth, enabling blood to flow freely. As a person ages, the arteries normally become thicker and less elastic, and their calcium content increases. This natural ' hardening' process occurs throughout the artery system.
Atherosclerosis, by contrast, affects only the larger arteries. As the plaque builds up, the inner layers of the artery walls become thick and irregular. Fat, cholesterol, and other materials accumulate in certain areas. This gradual build-up over a long period of time reduced the circulation of blood and increases the risk of heartattack, stroke, and other serious arterial diseases. A person having atherosclerosis will often experience symptoms of angina, stroke, and claudication. All of the symptoms are caused by insufficient blood flow due to atherosclerosis. Initially, the deposits of fat-containing cells that lead to atherosclerosis are only slight streaks, and are called fatty streaks. As the fatty streaks enlarge, they invade the deeper layers of the artery walls, causing scarring and calcium deposits. Large deposits are called athermas or plaques. The plaques calcify into a chalky substance. The plaque consists of a firm shell that contains calcium with areas of fatty material, and a centre consisting of soft cholesterol. As the plaque deposits grow the cardiac muscle beyond the blockage becomes deprived of blood, a condition known as myocardial ischemia. The healthy elastic wall of the artery changes into dead and unresponsive scartissue. If insufficient blood flow continues, the cardiac muscle dies, causing myocardial infarction. As the degeneration of the endothelial lining of the arteries continues, the lining may be damaged. Bloodplatelets stick to the site of injury, and a chemical signal is activated that promotes an influx of cholesterol.
The symptoms of atherosclerosis develop slowly as the development of the occlusion of the arteries progresses. Symptoms include angina, stroke, and claudication. The specific symptoms depend on which artery or arteries are occluded. If the leg arteries are affected, symptoms usually include numbness, fatigue, or pain in the leg. Occlusion of the coronary arteries may lead to angina or even a heartattack. When atherosclerosis occurs in the coronary arteries, it can lead to myocardial ischemia, an insufficient flow of blood to the heart. If the duration of ischemia is brief, the damage is reversible. However, if the duration of ischemia is longer than 40 to 60 minutes, irreversible damage may occur, and the parts of the heart muscle deprived of blood become permanently damaged, leading to myocardial infarction. Other commonly affected large arteries include the carotid arteries and the abdominal aorta. Initially, the symptoms of atherosclerosis are more likely to occur during exercise or strenuous activity than at rest. The symptoms develop during exercise because the arteries cannot supply the muscles with enough oxygen and nutrients. This process results in the build-up of by-products in the muscle that cannot be removed efficiently because of the occluded blood flow. This build-up of waste products, such as lactic acid, causes pain. It is similar to the build-up of lactic acid in muscles due to overexertion. As the narrowing of the arteries increases, the symptoms become prevalent with less and less exertion. The symptoms generally disappear after a few minutes of rest. However, the occlusion can be so severe that even the resting muscle does not get enough blood flow and the symptoms may be experienced even when sitting still. Research Atherosclerosis
The left atrium is a small upper cavity of the heart. Oxygen rich blood returns from the lungs through the four pulmonary veins into the smooth chamber of the left atrium. The chamber is constructed of two overlapping layers of muscle: a superficial layer and an inner layer, composed of many small bundles. The wall of the chamber is slightly thicker and more powerful than the right atrium. As the heart contracts (ventricular systole), blood flows into the ascending aorta through the aortic arch. As the heart relaxes (ventriclediastole), the blood flows through the mitral valve to the left ventricle. The right atrium is a small upper cavity of the heart that holds about three-and-a-half tablespoons of blood. It serves as the receiving chamber for all the venous blood (short of oxygen and laden with carbon dioxide) returning through the superior and inferior vena cava, and from many minute blood vessels that drainblood from the walls of the chamber itself. The right atrium is slightly larger than the left atrium, which is slightly more powerful. The walls of the right atrium are less than an eighth of an inch thick. Two layers of muscle form the wall. The superficial layer spans both atria, and the inner layer, composed of many small bundles, arches over the atrial cavity at right angles to the superficial layer. As the heart contracts (ventricular systole), the blood is pushed through the pulmonary valve into pulmonary circulation. As the heart relaxes (ventricular diastole), the blood exits the right atrium through the tricuspid valve to the right ventricle. In the upper part of the right atrium there is a small patch of special hearttissue called the sinus node or the sinoatrial node. It is the heartspacemaker, triggering the heartbeat and establishes its rate. Research Atrium
The celiac artery (celiac trunk) branches from the descending aorta near the opening in the diaphragm. It is a short thick branch of artery about an inch in length and divides into three branches, the gastric, hepatic, and splenic. It supplies the intestines, spleen, and liver. Research Celiac Artery
The celiac ganglia are large clusters of nerve fibres which are related to the sympathetic nervous system. They are located on either side of the aorta, near where the celiac artery begins. Nerves extend from the sympathetic trunk to the celiac ganglia and from there to the stomach, gall bladder, bile ducts, adrenal glands, and further to the inferior and superior mesenteric ganglia, which innervate the intestines. Research Celiac Ganglia
Two common iliac arteries branch from the abdominal portion of the aorta. Each artery is about five centimeters in length and descends downward and outward toward the edge of the pelvis. The common iliac artery divides into the internal and external iliac arteries and supplies the pelvis and lower extremities. Research Common Iliac Artery
Like all body organs, the heart needs a supply of blood to bring it oxygen. It cannot get oxygen from the blood within its chambers, which passes through too quickly and under too great a pressure, and in the right side is very low in oxygen. Instead, the muscle that makes up the wall of the heart, the myocardium, receives oxygen-rich blood from a system of small arteries that branch from the aorta. These are called the coronary arteries. They cross over the hearts surface, dividing and sending tiny branches into the heart muscle. The two coronary arteries are no wider than a drinking straw.
The right coronary artery lies in a groove between the right atrium and right ventricle and loops around the lower side and to the rear of the heart like a crown. Hence the name, coronary. This artery supplies blood to the thick muscle of the right ventricle.
On the other side, the left coronary artery divides almost immediately into two large branches, one of which (the anterior descending branch) passes over the front of the heart toward the tip. The other branch (the circumflex branch) lies in a groove between the left atrium and left ventricle. This artery supplies blood to the muscle of the left ventricle. The anterior descending branch supplies the front surface and tip of the heart and the front part of the septum. The circumflex branch supplies the portion of the left ventricular wall away from the septum. From the large coronary vessels, smaller branches arise, which divide and insert into the heart muscle, supplying its nutritional needs. If a blood clot occludes some part of the coronary artery, as in coronary thrombosis or coronary embolism, the cells of the heart are deprived of oxygen and soon die. This is called myocardial infarction. Research Coronary Artery
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Aneurysm
