Your heartbeat is a sign of life itself. Even when you drift off

Transcription

1 37 1 The Circulatory System Section 37 1 Your heartbeat is a sign of life itself. Even when you drift off to sleep, your heart continues to beat at a steady rhythm. Why is this process so important that it must keep going even when you sleep? Each breath you take brings air into your respiratory system. The oxygen in that air is needed by the trillions of cells in your body. Your heart is essential in delivering that oxygen. Its beating produces the force to move oxygen-rich blood through the circulatory system. Interrelationships between the circulatory and respiratory systems supply cells throughout the body with the nutrients and oxygen they need to stay alive. Functions of the Circulatory System Organisms composed of a small number of cells do not need a circulatory system. Most cells in such organisms are in direct contact with the environment. Oxygen, nutrients, and waste products can easily diffuse back and forth across cell membranes. Larger organisms, however, cannot rely on diffusion. Most of their cells are not in direct contact with the environment, and substances made in one part of the organism may be needed in another part. In a way, this same problem is faced by the millions of people living in a large city. Cities have transportation systems that move people, goods, and waste material from one place to another. The transportation system of a city is its streets, highways, and rail lines. The transportation system of a living organism is its circulatory system. Humans and other vertebrates have closed circulatory systems. This means that a circulating fluid called blood is contained within a system of vessels. The human circulatory system consists of the heart, a series of blood vessels, and the blood that flows through them. Print: SECTION RESOURCES Laboratory Manual B, Chapter 37 Lab Teaching Resources, Lesson Plan 37 1, Adapted Section Summary 37 1, Adapted Worksheets 37 1, Section Summary 37 1, Worksheets 37 1, Section Review 37 1, Enrichment Reading and Study Workbook A, Section 37 1 Adapted Reading and Study Workbook B, Section 37 1 Key Concepts What are the structures of the circulatory system? What are the three types of blood vessels in the circulatory system? Vocabulary myocardium atrium ventricle pulmonary circulation systemic circulation valve pacemaker aorta artery capillary vein atherosclerosis Reading Strategy: Using Visuals Before you read, preview Figure Make a list of questions about the illustration. As you read, write down the answers to the questions. Figure 37 1 These roads form a transportation system. Using Analogies How is the human circulatory system like the streets and highways of a large city? Probeware Lab Manual, What factors affect heart rate? Technology: itext, Section 37 1 Animated Biological Concepts DVD, 43 Human Circulation Transparencies Plus, Section 37 1 Lab Simulations CD-ROM, Cardiovascular 1: The Beating Heart Virtual Labs, Lab 20 1 FOCUS Objectives Identify the functions of the human circulatory system Describe the structures of the circulatory system Name the three types of blood vessels in the circulatory system Describe blood pressure. Vocabulary Preview Explain that the circulatory system consists of the heart and blood vessels. Then, call students attention to the vocabulary words and ask: Which words refer to structures of the heart, and which words refer to types of blood vessels? (Myocardium, atrium, ventricle, valve, aorta, and pacemaker refer to structures of the heart. Artery, capillary, and vein refer to types of blood vessels.) Reading Strategy Have students write the headings and subheadings in outline form. As they read, have them fill in the outline with enough details to make each topic clear and informative. 2 INSTRUCT Functions of the Circulatory System Build Science Skills Calculating Help students appreciate how much blood is pumped through the circulatory system. Tell them that the heart pumps an average of about 5 L of blood per minute. Ask: How many liters of blood are pumped through the circulatory system in an average lifespan of 75 years? (Almost 200,000,000 L) Answer to... Figure 37 1 Blood vessels are like the streets and highways that carry materials to each part of a city. Circulatory and Respiratory Systems 943

2 37 1 (continued) The Heart Demonstration Display a three-dimensional model of the heart that can be taken apart to show the inside. Call on students to identify each part of the heart described in the text, including the septum, atria, and ventricles. Have students trace the route of blood through the heart. Point out the valves, and explain how they let blood flow in only one direction. STRUCTURES OF THE HEART Figure 37 2 The circulatory system consists of the heart, a series of blood vessels, and the blood. Notice the valves between the atria and ventricles and those between the ventricles and the blood vessels leaving the heart. The valves prevent blood from flowing backward. Superior Vena Cava Large vein that brings oxygen-poor blood from the upper part of the body to the right atrium Pulmonary Veins Bring oxygen-rich blood from each of the lungs to the left atrium Aorta Brings oxygen-rich blood from the left ventricle to the body Pulmonary Arteries Bring oxygen-poor blood to the right or left lung Left Atrium Use Visuals Figure 37 2 Help students understand how blood flows through the heart. Explain that blood always leaves the heart through arteries and always returns to the heart through veins. Check students understanding of how the heart pumps blood by asking: Where is blood pumped by the atria? (To the ventricles) Where is blood pumped by the ventricles? (To the lungs and the rest of the body) Pulmonary Valve Prevents blood from flowing back into the right ventricle after it has entered the pulmonary artery Right Atrium Tricuspid Valve Prevents blood from flowing back into the right atrium after it has entered the right ventricle Inferior Vena Cava Vein that brings oxygen-poor blood from the lower part of the body to the right atrium Right Ventricle Aortic Valve Prevents blood from flowing back into the left ventricle after it has entered the aorta Mitral Valve Prevents blood from flowing back into the left atrium after it has entered the left ventricle Left Ventricle Septum For: The Heart activity Visit: PHSchool.com Web Code: cbe-0371 Students learn the parts of the heart and see the flow of blood through the heart. For: The Heart activity Visit: PHSchool.com Web Code: cbp-0371 The Heart As you can feel with your hand, your heart is located near the center of your chest. The heart, shown in Figure 37 2, which is composed almost entirely of muscle, is a hollow organ that is about the size of your clenched fist. The heart is enclosed in a protective sac of tissue called the pericardium (pehr-ih-kahrdee-um). In the walls of the heart, there are two thin layers of epithelial and connective tissue that form a sandwich around a thick layer of muscle called the myocardium. The powerful contractions of the myocardium pump blood through the circulatory system. UNIVERSAL ACCESS 944 Chapter 37 Inclusion/Special Needs Use a hands-on experience to help students appreciate the work of the heart. Have them squeeze a tennis ball once per second for two minutes without stopping. As they do, explain that this is how hard the heart works. Stress that the heart continues to work this way nonstop for life. Less Proficient Readers Help students understand the different types of blood vessels by having them make a graphic organizer, such as a compare/contrast table or Venn diagram, to summarize the similarities and differences among the three types. Advanced Learners Have students who need an extra challenge learn about heart valve defects. They should investigate types of defects and their causes, how they affect health, and whether they can be repaired surgically. Urge students to share what they learn in an oral report.

3 The heart muscle contracts on average 72 times a minute, pumping about 70 milliliters of blood with each contraction. This means that during one year, an average person s heart pumps more than enough blood to fill an Olympic-sized swimming pool. (An Olympic-sized swimming pool is about 2,000,000 liters: 0.07 liters 4320 beats per hour 24 hours 365 days = 2,649,024 liters.) Dividing the right side of the heart from the left side of the heart is the septum. The septum prevents the mixing of oxygen-poor and oxygen-rich blood. On each side of the septum are two chambers. The upper chamber, which receives the blood, is the atrium (plural: atria). The lower chamber, which pumps blood out of the heart, is the ventricle. The heart has four chambers in total two atria and two ventricles. Circulation Through the Body The heart functions as two separate pumps. Figure 37 3 shows the circulation of blood through the body. The right side of the heart pumps blood from the heart to the lungs. This pathway is known as pulmonary circulation. In the lungs, carbon dioxide leaves the blood and oxygen is absorbed. The oxygen-rich blood then flows into the left side of the heart and is pumped to the rest of the body. This pathway is called systemic circulation. Blood that returns to the right side of the heart is oxygen-poor because cells have absorbed much of the oxygen and loaded the blood with carbon dioxide. At this point, it is ready for another trip to the lungs. Circulation Through the Heart Blood enters the heart through the right and left atria. As the heart contracts, blood flows into the ventricles and then out from the ventricles to either the body or the lungs. There are flaps of connective tissue called valves between the atria and the ventricles. Blood moving from the atria holds the valves open. When the ventricles contract, the valves close, which prevents blood from flowing back into the atria. At the exits from the right and left ventricles, there are valves that prevent blood that flows out of the heart from flowing back in. This system of valves keeps blood moving through the heart in one direction, like traffic on a one-way street. The one-way flow increases the pumping efficiency of the heart. The valves are so important to heart function that surgeons often attempt to repair or replace a valve that has been damaged due to disease. Figure 37 3 The circulatory system is divided into two pathways. Pulmonary circulation carries blood between the heart and the lungs. Systemic circulation carries blood between the heart and the rest of the body. Observing What kind of blood oxygen-rich or oxygen-poor leaves the lungs and returns to the heart? Capillaries of head and arms Superior vena cava Pulmonary vein Capillaries of right lung Inferior vena cava Aorta Pulmonary artery Capillaries of left lung Capillaries of abdominal organs and legs Use Visuals Figure 37 3 Explain that the redcolored blood vessels carry oxygen-rich blood and the bluecolored blood vessels carry oxygenpoor blood. Add that most of the oxygen-rich blood is carried in the arteries and most of the oxygen-poor blood is carried in the veins. The only exceptions are the pulmonary artery and vein. Ask: Why are the pulmonary artery and vein exceptions in this way? (Because they carry blood to and from the lungs, where the blood picks up oxygen) Remind students that the red and blue color scheme is a convention that makes it easier to follow the flow of blood through the circulatory system, but the blue does not represent the actual color of oxygen-poor blood. Build Science Skills Using Models Point out that a good model of a heart valve is an automatic door that opens in only one direction, like the doors typically found in supermarkets. Ask: How is a heart valve like a one-way door? (Like a one-way door, the heart valve allows only one-way flow through an opening.) Use Community Resources Invite a nurse or technician who administers electrocardiograms, or ECGs, to speak to the class. Suggest that the speaker explain how ECGs are performed and what they measure. If possible, have the speaker bring a sample ECG printout to class and use it to explain to students how ECGs are interpreted. Have students write a paragraph summarizing what they learn. What is the function of the heart valves? HISTORY OF SCIENCE William Harvey s contributions One scientist is known above all others for his contributions to our understanding of the human circulatory system. That scientist is William Harvey, the English physician whose 1628 book on the circulation of blood was a landmark publication. Until Harvey s time, there were many misconceptions about the blood and circulation. For example, it was believed that blood formed in the liver, that it moved very sluggishly if at all, and that pulmonary and systemic blood were not connected. Harvey dissected cadavers and studied living patients to prove many of these beliefs wrong. He determined that blood is forced by the pumping of the heart in a circular pathway throughout the body, leaving the heart via the arteries and returning to the heart through the veins. Harvey also explained how the valves in the heart and veins keep blood flowing in just one direction. Answers to... The function of the heart valves is to prevent any backflow of blood from the ventricles to the atria and from the aorta and pulmonary artery to the ventricles. Figure 37 3 Oxygen-rich blood leaves the lungs and returns to the heart. Circulatory and Respiratory Systems 945

4 37 1 (continued) Make Connections Health Science Point out that artificial pacemakers are implanted in people whose hearts need help maintaining a normal rate of contractions. The battery-operated pacemaker sends electrical impulses to the heart whenever it starts to beat abnormally. For example, if the heart starts to beat too slowly, the pacemaker sends electrical impulses that stimulate the heart to beat faster. Ask: Based on how the artificial pacemaker works, how do you think the heart s natural pacemaker works to control the heart? (By sending out electrical impulses) Blood Vessels Demonstration Show students the direction in which blood travels in veins using a demonstration originally designed by William Harvey. Select a student volunteer who has obvious veins in the forearms. Press down with your fingers on one of the more prominent veins near the wrist. While continuing to press down on the vein, run a fingertip along the same vein toward the elbow. The vein will disappear and blood will not flow back into the vein until you release the pressure near the wrist. Ask: In which direction is blood flowing in the vein? (From the wrist to the elbow) What prevented the blood from flowing back into the vein after it was pushed toward the elbow? (Oneway valves in the vein) Sinoatrial (SA) node Atrioventricular (AV) node Conducting fibers Figure 37 4 The signal to contract spreads from the sinoatrial node to the cardiac muscle cells of the atria, causing the atria to contract. The impulse is picked up by the atrioventricular node, which transmits the impulse to muscle fibers in the ventricles, causing the ventricles to contract. Predicting In times of stress, does the heart beat faster or slower? Heartbeat There are two networks of muscle fibers in the heart, one in the atria and one in the ventricles. When a single fiber in either network is stimulated, all the fibers are stimulated and the network contracts as a unit. Each contraction begins in a small group of cardiac muscle cells the sinoatrial node located in the right atrium. Because these cells set the pace for the heart as a whole by starting the wave of muscle contraction through the heart, they are also called the pacemaker. As shown in Figure 37 4, the impulse spreads from the pacemaker (SA node) to the network of fibers in the atria. It is picked up by a bundle of fibers called the atrioventricular node and carried to the network of fibers in the ventricles. When the network in the atria contracts, blood in the atria flows into the ventricles. When the muscles in the ventricles contract, blood flows out of the heart. This two-step pattern of contraction makes the heart a more efficient pump. Your heart can beat faster or more slowly, depending on your body s need for oxygen-rich blood. During vigorous exercise, your heart rate may increase to about 200 beats per minute. Although the heartbeat is not directly controlled by the nervous system, the autonomic nervous system does influence heart rate. Neurotransmitters released by the sympathetic nervous system increase heart rate. Those released by the parasympathetic nervous system decrease heart rate. Blood Vessels Blood leaving the left side of the heart is loaded with oxygen from the lungs. When it leaves the left ventricle, the blood passes into a large blood vessel known as the aorta. The aorta is the first of a series of blood vessels that carry the blood on its round trip through the body and back to the heart. As blood flows through the circulatory system, it moves through three types of blood vessels arteries, capillaries, and veins. Arteries Large vessels that carry blood from the heart to the tissues of the body are called arteries. Arteries are the superhighways of the circulatory system. Except for the pulmonary arteries, all arteries carry oxygen-rich blood. Arteries have thick walls that help them withstand the powerful pressure produced when the heart contracts and pushes blood into the arteries. FACTS AND FIGURES All about the heart The nervous system influences the heart rate, but does not directly control contractions of cardiac muscle. In fact, the heart may keep beating for several minutes after it is removed from the body. The lub-dub sound of the heartbeat is produced by vibrations in the walls of the heart when the heart valves snap shut. The heart of a newborn beats about twice as fast as the heart of an adult, at about 140 beats per minute compared with about 70 beats per minute. Throughout a lifetime, the average person s heart beats about 3 billion times. To do all this work, cardiac muscle requires a lot of oxygen. Heart tissue uses about 80 percent of the oxygen supplied to it, while most other tissues use about 25 percent of the oxygen supplied to them. 946 Chapter 37

5 Connective tissue Smooth muscle Endothelium Artery Arteriole Endothelium Capillary Venule Vein Connective tissue Smooth muscle Endothelium Valve Use Visuals Figure 37 5 Point out the horizontal arrow in the figure, and explain that it shows the direction of blood flow through the blood vessels. Check students understanding of the different types of blood vessels by having them complete the analogy: arterioles are to arteries as venules are to. (veins) Challenge students to identify how the drawings of the vein and artery differ. (The vein has a valve; the artery does not. The artery has a thicker layer of smooth muscle than the vein does.) Figure 37 5 shows that the walls contain connective tissue, smooth muscle, and endothelium. The elastic connective tissue allows an artery to expand under pressure. Contractions of the smooth muscle regulate the diameter of an artery. Capillaries The smallest of the blood vessels are the capillaries. Capillaries are the side streets and alleys of the circulatory system. The walls of capillaries are only one cell thick, and most are so narrow that blood cells must pass through them in single file. The real work of the circulatory system bringing nutrients and oxygen to the tissues and absorbing carbon dioxide and other waste products from them is done in the capillaries. Veins Once blood has passed through the capillary system, it must be returned to the heart. This is the job of the veins. As with arteries, the walls of veins contain connective tissue and smooth muscle. Large veins, such as those shown in the leg in Figure 37 6, contain valves that keep blood moving toward the heart. Many veins are located near and between skeletal muscles. When you exercise, contracting these muscles helps force blood through the veins. Blood flow through the veins of the arms and legs often occurs against the force of gravity. Exercise helps to keep blood from accumulating in the limbs and stretching the veins out of shape. If the walls around the veins weaken from lack of activity, the valves can weaken. This causes blood to pool in the veins, producing a condition known as varicose veins. What happens in the capillaries? Figure 37 5 In the circulatory system, there are three types of blood vessels arteries, capillaries, and veins. The walls of these vessels contain connective tissue, smooth muscle, and endothelium. Valve closed Valve open Valves closed Build Science Skills Inferring Students are likely to be aware that they can monitor the beating of the heart by feeling a pulse in the wrist. Ask: Why can you feel a pulse in your wrist every time your heart beats? (Arteries are somewhat elastic, so they expand slightly each time the heart pumps blood into the aorta. This expansion can be felt as a pulse in arteries that are close to the surface of the body, such as those in the wrist.) Figure 37 6 Contraction of skeletal muscles helps move blood in veins toward the heart. Drawing Conclusions What role do valves play in large veins? FACTS AND FIGURES Aorta, CEO of arteries The aorta has been called the CEO of the arterial blood circulation system. It is the principal artery in the body, from which almost all other arteries divide and subdivide, down to the tiniest arteriole. At its maximum diameter, where it begins at the left ventricle, the aorta is almost 3 cm in diameter. From there, it arches back and down through the chest and diaphragm to the abdomen. Some of the major branches of the aorta as it travels through the body are the coronary arteries, which supply blood to the heart; the innominate, subclavian, and carotid arteries, which supply blood to the head, neck, and arms; and the right and left iliac arteries, which supply blood to the legs. The aorta can develop atherosclerosis, or fat deposits on the walls. Without treatment, this can contribute to high blood pressure and potentially fatal bulges in the aortic wall called aneurysms. Answers to... Nutrients and oxygen are delivered to the tissues, and carbon dioxide and other waste products are absorbed by the blood. Figure 37 4 It beats faster. Figure 37 6 They keep blood flowing toward the heart. Circulatory and Respiratory Systems 947

6 37 1 (continued) Blood Pressure Address Misconceptions Many people think that it is natural for blood pressure to increase significantly with age. Explain that this is a myth. It is based on the tendency of older people to have high blood pressure because of years of high-fat diets and other behaviors that increase the chances of developing high blood pressure. Emphasize that high blood pressure is unhealthy at any age. Also, point out that young people can develop high blood pressure, especially if they are overweight, do not exercise, or have certain illnesses. Use Community Resources Invite a school nurse or other health professional to bring a sphygmomanometer to class and show students how it is used to measure blood pressure. Encourage the health professional to explain how both systolic and diastolic pressures are read and what each measures. If possible, after the demonstration, give interested students a chance to use the sphygmomanometer to take each other s blood pressure while being supervised. Cardiovascular Advances William Harvey correctly described the role of the heart in the circulation of blood more than three centuries ago. Since then, advances in this area have improved the lives of many people with heart disease Alexis Carrel Carrel paves the way for organ transplantation by developing techniques for rejoining severed blood vessels. Blood Pressure Like any pump, the heart produces pressure. When the heart contracts, it produces a wave of fluid pressure in the arteries. The force of the blood on the arteries walls is known as blood pressure. Blood pressure decreases when the heart relaxes, but the system still remains under pressure. It s a good thing, too. Without that pressure, blood would stop flowing through the body. Medical workers can measure blood pressure with a device called a sphygmomanometer (sfig-moh-muh-nahm-uh-tur). A cuff is wrapped around the upper arm. Air is pumped into the cuff until blood flow through an artery is blocked. As the pressure is released, the worker listens to the pulse with a stethoscope and records two numbers from a pressure gauge. The first number is the systolic pressure the force felt in the arteries when the ventricles contract. The second number is the diastolic pressure the force of the blood felt in the arteries when the ventricles relax. A typical blood pressure reading for a healthy person is 120/80. The body normally regulates blood pressure in two ways. Sensory receptors at several places in the body detect the level of blood pressure, sending impulses to the medulla oblongata region of the brain stem. When blood pressure is too high, the autonomic nervous system releases neurotransmitters that cause the smooth muscles in blood vessel walls to relax, lowering blood pressure. When blood pressure is too low, neurotransmitters are released that elevate blood pressure by causing these smooth muscles to contract Willem Einthoven Einthoven wins a Nobel Prize for his invention of the electrocardiograph (EKG), a device used to measure tiny electric currents produced by the heart Charles R. Drew Drew develops a method to process and preserve blood plasma so that it can be stored and shipped Dwight Harken Charles Bailey Harken and Bailey independently perform operations to open up closed heart valves in patients. Twelve years later, Harken replaces a heart valve with an artificial valve FACTS AND FIGURES 948 Chapter 37 Blood pressure s ups and downs Blood pressure rises and falls throughout life and even throughout the day. Babies and children usually have much lower blood pressure than adults, and blood pressure is generally lowest during sleep and highest during the morning. Blood pressure also rises during exercise and periods of emotional excitement. Weight gain is usually associated with an increase in blood pressure. Regulation of blood pressure s ups and downs is complex. When blood pressure falls, it causes the release of the kidney enzyme renin. Renin, in turn, activates the hormone angiotensin, which causes the arterioles to constrict. Constriction of the arterioles leads to an increase in blood pressure. Angiotensin also stimulates the adrenal gland to release aldosterone, which causes the kidney to retain salt. This leads to an increase in water in the blood, and the greater blood volume causes an increase in blood pressure.

7 The kidneys, which remove water from the blood, also help to regulate blood pressure. Hormones produced by the heart and other organs cause the kidneys to remove more water from the blood when blood pressure is high. This action reduces blood volume, thereby lowering the blood pressure. What instrument measures blood pressure? Diseases of the Circulatory System Unfortunately, diseases of the circulatory system are all too common. Cardiovascular diseases especially heart disease and stroke are among the leading causes of death and disability in the United States. High blood pressure and a condition known as atherosclerosis (ath-ur-oh-skluh-roh-sis) are two of the main causes of cardiovascular disease. Atherosclerosis is a condition in which fatty deposits called plaque build up on the inner walls of the arteries. High Blood Pressure High blood pressure, or hypertension, is defined as a sustained elevated blood pressure of 140/90 or higher. The heart is forced to pump against increased resistance, which enlarges the myocardium. This forces the heart to work harder, which may weaken or damage the heart muscle and blood vessels. People with high blood pressure are more likely to develop coronary heart disease and to suffer from other diseases of the circulatory system. Hypertension increases the risk of heart attack and stroke Wilson Greatbatch Greatbatch invents the implantable pacemaker. The mechanical device emits electrical signals that keep the heart beating normally Andreas Gruentzig Gruentzig performs the first angioplasty by inserting a hollow tube containing a tiny uninflated balloon into a patient s coronary artery. The balloon is inflated, opening up the blocked area and restoring blood flow to the heart. Use the Internet or a library to find out more about the research conducted by one of these scientists. Then, write a summary of the contributions of the scientist to the field of medicine Laman Gray Robert Dowling Gray and Dowling implant the first completely self-contained artificial heart into a patient HISTORY OF SCIENCE Other cardiovascular advances The first American surgeon to perform a human heart transplant was Dr. Norman E. Shumway. In 1968, just one year after the first human heart transplant was performed by Christiaan Barnard, Shumway transplanted a heart into a 54-year-old man whose own heart had been injured by a viral infection. Although this patient survived for only 15 days following transplant surgery, Shumway went on to perform many successful heart 1982 William DeVries DeVries leads a team of doctors to implant the Jarvik-7 artificial heart in a patient, who lives for 112 days. transplant surgeries. Shumway also made other achievements in heart surgery, including the transplantation of heart valves. One of the reasons early heart transplants failed was because the donor heart was rejected by the patient s immune system. The development of effective immunosuppressant drugs greatly increased the success rate of transplantation. Diseases of the Circulatory System Demonstration Give students a hands-on demonstration of how atherosclerosis increases blood pressure and the work the heart has to do to pump blood. Obtain a bicycle pump and a piece of rubber tubing that fits over the air nozzle of the pump. Give several volunteers a chance first to pump air through the open tube, and then to pump air through the tube when you squeeze it almost closed. Urge students to describe to the class the difference in the amount of work required when the tube was open and when it was almost closed. Conclude by saying that this is similar to the way atherosclerosis narrows the arteries, causing the heart to work harder and blood pressure to increase. Explain to students that thousands of heart transplants have been performed since the first heart transplant was performed by Christiaan Barnard in By 1995, heart transplants had a 90 percent success rate. However, heart transplants are still usually reserved for patients who have the most serious types of heart disease that cannot be treated with drugs or other types of surgery. Encourage students to select different scientists so that all of the scientists are covered. After students have completed their summaries, call on volunteers to read about each of the scientists in the timeline in chronological order. Ask students which scientist they think made the most valuable contribution. Have them explain their choices. Answer to... A sphygmomanometer measures blood pressure. Circulatory and Respiratory Systems 949

8 37 1 (continued) NSTA Download a worksheet on the cardiovascular system for students to complete, and find additional teacher support from NSTA SciLinks. Build Science Skills Using Tables and Graphs Challenge students to use library sources to find data tables and graphs that relate behavioral variables such as smoking, sedentary lifestyle, and high-fat diet to the risk of circulatory disorders such as high blood pressure, heart attack, and stroke. Call on volunteers to explain their tables and graphs to the class by summarizing in words what the data show in numbers. 3 ASSESS Evaluate Understanding Call on students at random to define each of the Vocabulary terms. Call on other students to correct any errors. NSTA For: Links on the cardiovascular system Visit: Web Code: cbn-0371 Consequences of Atherosclerosis Atherosclerosis is particularly dangerous in the coronary arteries, which bring oxygen and nutrients to the heart muscle itself. If one of these arteries becomes blocked, part of the heart muscle may begin to die from a lack of oxygen. If enough heart muscle is damaged, a condition known as a heart attack occurs. The symptoms of a heart attack include nausea, shortness of breath, and severe, crushing chest pain. People who show these symptoms need immediate medical attention. New drugs are available that can increase blood flow enough to save the heart, but they must be given in the early stages of a heart attack to save the heart muscle and prevent death. Blood clots that can form as a result of atherosclerosis may break free and get stuck in one of the blood vessels leading to a part of the brain. This condition is known as a stroke. Brain cells served by the particular blood vessel gradually die from a lack of oxygen, and brain function in that region may be lost. Depending on what part of the brain they affect, strokes may cause paralysis, loss of the ability to speak, and death. Circulatory System Health Like other diseases, cardiovascular diseases are easier to prevent than to cure. Some of the ways of avoiding cardiovascular disease include getting regular exercise, eating a balanced diet, and avoiding smoking. Exercise makes your heart muscle stronger and more efficient. It also helps control your weight, reduces body fat, and reduces stress. A diet low in saturated fat and cholesterol can reduce your risk of developing heart disease as well. High levels of fat and cholesterol in the blood increase the likelihood that it will be deposited onto the artery walls. This process begins in childhood and worsens as you get older. For this reason, you should limit your intake of foods with saturated fat. A low-fat diet will also help control your weight. Being overweight enlarges the circulatory system, causing the heart to pump harder to force blood through it. The cardiovascular system is also damaged by smoking. You will learn more about the effects of smoking later in this chapter. Reteach Have students trace the path of blood through the heart in Figure 37 3 and name each of the structures through which the blood passes. Make sure students use reliable sources, especially on the Internet. The American Heart Association and National Institutes of Health are good Internet sources for additional information. Students commentaries should contain only accurate, relevant information and be written in a succinct, journalistic style. If your class subscribes to the itext, use it to review the Key Concepts in Section Chapter Section Assessment 1. Key Concept List the structures of the circulatory system. 2. Key Concept Compare the functions of the three types of blood vessels in the circulatory system. 3. Describe the path of blood circulation through the body Section Assessment 1. Heart, blood vessels, and blood 2. Arteries carry blood from the heart to the tissues; capillaries bring food and oxygen to the tissues and absorb carbon dioxide and waste products; veins carry blood back to the heart from the rest of the body. 3. The right side of the heart pumps blood from the heart to the lungs. Oxygen-rich blood from the lungs returns to the left side of the heart, where it is pumped to the rest of the 4. What is the role of the nervous system in heartbeat regulation? 5. Critical Thinking Inferring If you were standing, would you expect the blood pressure to be higher in your arm or in your leg? Explain your answer. Cause and Effect Use library or Internet resources to research the connection between a high-fat diet and cardiovascular disease. Write a short commentary that could be used on a television news program that explains the connection. Hint: Prepare a cause-and-effect diagram to organize your ideas. body. The veins return oxygen-poor blood to the right side of the heart. 4. Neurotransmitters released by the sympathetic nervous system increase heartbeat. Those released by the parasympathetic nervous system decrease heartbeat. 5. It would be higher in your arm because your arms are physically closer to your heart. Blood pressure decreases as you move farther from the heart.