Clumps and Bumps: A Look at Atherosclerosis Student Activity Page 4B Introduction Chances are that every one in your class knows somebody who has had a heart attack, but how many really understand what caused that heart attack? Chances are also good that the person who had the heart attack was older than you and your classmates, so you probably don t think of people your age having heart problems. In this activity, you will have a chance to see that the heart attacks occurring in older people actually began very early in life. The pictures of arteries in this activity were taken from people aged 15-24 years old. The blockages like those seen in the photos have been found in children much younger! The good news is that if you learn how to make good choices and take care of your body, you have a very good chance of avoiding the heart problems you will be studying. Background Atherosclerosis (ath-er-o-skle-ro-sis) is the hardening and narrowing of arteries. It is a slow, progressive disease that starts in childhood. It is caused by the slow buildup of plaque (plak) inside the walls of our arteries. Arteries are blood vessels that carry oxygen-rich blood away from the heart to other parts of the body. The coronary arteries are small blood vessels that carry oxygen-rich blood to the heart muscle itself, supplying food and oxygen needed to keep our hearts beating. (Note: the pulmonary arteries carry oxygen-poor blood away from the heart to the lungs). Plaque is made up of fat, cholesterol, calcium, and other substances found in blood. The presence of oxidized LDL (low density lipoprotein) activates scavenger white blood cells, called macrophages. The macro-phages begin to ingest as much of the oxidized LDL as possible and change into foam cells as a result. The newly formed foam cells begin releasing signals that initiate an immune response in the body. The buildup of plaque inside the walls of an artery narrows the inner diameter of that artery and, in time, may restrict blood flow. Plaque can be hard and stable or soft and unstable. Hard plaque causes artery walls to thicken and harden. Soft plaque is more likely to break away from the walls and enter the bloodstream. This can cause a blood clot that can partially or totally block the flow of blood in the artery. When this happens, the organ supplied by the blocked artery starves for blood and oxygen. The organ s cells may either die or suffer severe damage. 13
See Figure 1 (following page) which illustrates a cross-section of an artery with the layers of the artery labeled and the channel within the artery. Atherosclerosis can affect the arteries of the brain, heart, kidneys, and the arms and legs. As plaque builds up, it can cause serious diseases and complications. These include: Coronary artery disease Angina pectoris Heart attack Sudden death Cerebrovascular disease Transient ischemic attack (TIA) or mini strokes Stroke Peripheral arterial disease When atherosclerosis is in the early stages, the size of plaques in arterial walls can be reduced by eating a healthy diet and exercising regularly. However, once atherosclerosis reaches advanced stages, arteries will be permanently damaged in spite of diet and exercise. Background retrieved and modified from the National Heart Lung and Blood website on April 14, 2005 http://www.nhlbi.nih.gov/health/dci/diseases/atherosclerosis/ Atherosclerosis_WhatIs.html 14
Figure 1 Layers of a Typical Artery close-up of Intima intima Photomicrograph courtesy of PDAY Funded by the National Heart, Lung, and Blood Institute NCT00005679 Figure 1 Layers of a Typical Artery 1. Intima inner layer of endothelial cells embedded in extracellular matrix 2. Adventitia outer most variable layer with dense fibroelastic connective tissue, nutrient vessels, and nerves 3. Media separated from intima by elastic lamina and has smooth muscle cells, elastic laminae, bundles of collagen fibers, and elastic fibrils all embedded in extracellular matrix adventitia media lumen 4. Lumen channel through which blood flows 15
Materials: (Per student) 1 Copy of Student Data Page 1 Copy of Student Activity Page per group if students work in groups Metric Ruler Transparency print of the Unit Square Grid on page 20 or graph paper Procedure: 1. Label the parts of each coronary artery photomicrograph on your Student Data Page. 2. You will now use the Unit Square Grid transparency to determine the open (unblocked) area of the coronary arteries shown in this activity. Each square in the unit square grid has an area of 1 cm 2. Find the picture of a typical coronary artery shown in Artery 1, Typical Coronary Artery Cross Section (on your Student Data Page). You will estimate the open area in the artery. a. First, place the Student Data Page with the Coronary Artery Pictures on a flat surface. b. Next, place the Unit Square Grid Page transparency over the picture of the artery. Using a transparency marker or wax pencil, trace the open space (lumen) of the coronary artery onto your Unit Square Grid. c. Label the tracing, Coronary Artery 1 Lumen. d. The white space inside the blood vessel is the lumen, or the space open for blood flow. You will be determining the area of the lumen only. Using the transparency marker or wax pencil, shade each box that has any part inside the boundary line you traced. See Figure 2 Estimating Open Area of Coronary Arteries Using a Unit Square Grid. 16
Figure 2 Estimating Open Area of Coronary Arteries Using a Unit Square Grid Note that each full square in the center of the open space of the blood vessel is 1 cm 2. In this figure there are two full squares and parts of 10 other squares. The part of each partial square that falls inside the artery lumen must be estimated. e. Now count the number of whole squares within the boundary of the lumen. Write this number down on your Student Data Page. f. Go back and estimate the area included in the partial squares within the boundary of the lumen. If 1/2 of a square is included, that represents 1/2 cm 2 or 0.50 cm 2. If 1/4 square is included, that area is 1/4 cm 2 or 0.25 cm 2. g. Add all these partial squares to your number of full squares. Be sure to keep up with all of the fractions! h. Record the result on your Student Data Page. i. Repeat this procedure for Artery 2, Coronary Artery Cross Section Showing Atherosclerosis. Label your tracing Coronary Artery 2. j. Repeat step i for Figures 3 and 4. Be sure to label each drawing with the correct Artery Number. (This number is included next to the picture of the artery on the Student Data Page.) 17