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Bi Sci 001 Wednesday April 7, 1999 Announcements: Test this friday Lecture notes: Valves Valves prevent backflow into the heart. The general term for the valves between the atria and the ventricles is atrioventricular valves. The specific term for the valve between the right atrium and right ventricle is the tricuspid valve. The valve between the left atrium and the left ventricle is the mitral valve. The general term for valves leading to blood vessels is semilunar valves. The specific term for the valve between the right ventricle and the pulmonary artery is the pulmonary valve. The valve leading from the left ventricle to the aorta is the aortic valve. The heart gets its oxygen and nutrients not from the blood flowign through it, but from the coronary arteries which are the first two arteries that come off the aorta. Blood Vessels Direction of heart flow: Heart --> arteries --> arterioles --> capillaries --> venules --> veins --> heart …continued. Arteries: carry blood away from the heart. They have a thick muscle layer and 2 elastic layers to resist the high pressure of the blood as it is ejected from the ventricles and to move the blood along as they rebound. Arterioles: smaller areteries with rings of smooth muscle which can contract and relax to control blood flow to an area. ( 2 definitions) Vasodilation: relaxation of the smooth muscle of the arteriole which results in enlargement of the vessel's Capillaries: smallest blood vessels, but the most extensive system. One cell thick. So narrow that red blood cells must line up single file. The pressure is so low that there is time for diffusion and gas exchange. Venules: smalls veins. Veins: return blood to the heart. Veins have a thinner muscle layer and less elastic tissue than arteries. They have valves to help prevent backflow of blood. Coordination of heart Beat When the ventricles contract, this part of the cardiac cycle is called systole. When they relax, it is called diastole. This is the basis of blood pressure readings. Heart muscle cells are capable of contracting on their own - without input from the autonomic nervous system. One group of specialized heart muscle cells at the juncture of the vena cava and the right atrium undergo action potentials without outside stimulation at a rate of between 70 - 80 times/minute. (sinoatrial node) This causes the atria to contract. The signal is also passed to the AV node - Atrioventricular node - on the floor of the right atrium. Fibers leading from the AV node cause the ventricles to contract - Purkinje fibers. Heart Facts Heart Disease has been the number 1 cause of death in the U.S. since 1910. Heart and Blood Vessel Disease causes 42% of all deaths in the U.S. today. (cancer-23% and all other causes 35%) Tobacco causes 20% of all deaths. About 1.5 million Americans will have a heart attack this year. About 1/3 of them die. 75% of heart disease is caused by atherosclerosis - clogging of arteries. Coronary arteries can be 2/3 blocked before and symptoms appear. Four reasons Why CVD Death Rates are Decreasing
Causes of blocked blood flow in arteries
Cocaine also causes fibrillation of the heart and strokes form uncontrolled blood pressure. (blowouts) Heart attack: death of part of the heart muscle as a result of interruption of blood flow. Can atherosclerosis be reversed? In many cases yes! If there has been calcification of the plaques, not much can be done except to stop further blockage (arteriosclerosis) Preliminary evidence is showing that a combination of a very low fat diet, stopping tobacco use, controlling hypertension, exercise and cholesterol controlling drugs (if necessary) has been shown to decrease the size of plaques. Coronary heart disease Asymptomatic: The period before enough decrease in blood supply occurs to produce symptoms of heart disease. Symptomatic: 1. Angina: chest pain. Hear Attack Risk Factors You can't change: Heredity You can change: Tobacco use |
