3.4. The Circulatory System

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The Circulatory System The human circulatory system is made up of the blood, the heart, and the blood vessels. The function of the circulatory system is to transport substances around the body.

Blood flows through the lungs (part of the respiratory system) to pick up oxygen and then flows through the body to deliver it to active cells.

Other waste substances are carried to the kidneys (an organ of the urinary system), where the substances are filtered out and excreted.

1 The Circulatory System The human circulatory system is made up of the blood, the heart, and the blood vessels. The function of the circulatory system is to transport substances around the body. It moves nutrients absorbed from the intestine to all of the body s cells. Blood flows through the lungs (part of the respiratory system) to pick up oxygen and then flows through the body to deliver it to active cells. Blood also carries wastes from the body tissues for disposal. It carries carbon dioxide to the lungs, where it is released into the air. Other waste substances are carried to the kidneys (an organ of the urinary system), where the substances are filtered out and excreted. Among the circulatory system s other vital functions are the regulation of body temperature and the transport of disease-fighting white blood cells to areas of the body where there are viruses or bacteria. 3.4 circulatory system the organ system that is made up of the heart, the blood, and the blood vessels; the system that transports oxygen and nutrients throughout the body and carries away wastes To watch a dissection of the organ systems of a fi sh, Parts of the Circulatory System The three main parts of the circulatory system are the blood, the heart, and the blood vessels. The heart pumps the blood through large blood vessels, called arteries, which branch into smaller and smaller blood vessels. The smallest blood vessels are called capillaries. In the capillaries, blood exchanges many substances with the surrounding tissues (Figure 1). After this exchange, blood flows into larger blood vessels called veins and eventually returns to the heart. Let s now look at these parts in detail. carbon dioxide out oxygen in capillaries in lungs, where gas exchange takes place arteries Blood Blood is a type of connective tissue that circulates throughout all parts of your body. The blood consists of four components (Figure 2): Red blood cells are the most plentiful of the body s blood cells. These cells make up almost half of the blood s volume. Red blood cells contain a protein called hemoglobin, which allows them to transport oxygen throughout the body. Hemoglobin makes the cells appear red. White blood cells are infection-fighting cells in the blood. They recognize and destroy invading bacteria and viruses. White blood cells make up less than 1 % of the volume of blood. They are the only blood cells to have a nucleus. Platelets are tiny cells that help in blood clotting. They also comprise less than 1 % of the blood. Plasma is a protein-rich liquid that carries the blood cells along. It makes up over half of blood s volume. veins carbon dioxide in heart capillaries in body tissues, where gas exchange takes place oxygen out Figure 1 The circulatory system connects all parts of the body. In this diagram, the oxygenated blood is shown in red. The deoxygenated blood is shown in blue. Note that this diagram is not to scale. Figure 2 Blood cells 3.4 The Circulatory System 83

DID YOU KNOW? Artificial Heart Dr. Tofy Mussivand, of the Medical Devices Centre at the University of Ottawa Heart Institute, researches and designs artifi cial hearts.

artery a thick-walled blood vessel that carries blood away from the heart vein a blood vessel that returns blood to the heart capillary a tiny, thin-walled blood vessel that enables the exchange of

Cardiac muscle tissue is a special type of muscle found only in the heart (Figure 3). All of the cardiac muscle tissue in each part of the heart contracts at the same time.

2 DID YOU KNOW? Artificial Heart Dr. Tofy Mussivand, of the Medical Devices Centre at the University of Ottawa Heart Institute, researches and designs artifi cial hearts. A patient needing a heart transplant may receive an artifi cial heart until a donor heart becomes available. artery a thick-walled blood vessel that carries blood away from the heart vein a blood vessel that returns blood to the heart capillary a tiny, thin-walled blood vessel that enables the exchange of gases, nutrients, and wastes between the blood and the body tissues The Heart The heart is made up of three different types of tissue: cardiac muscle tissue, nerve tissue, and connective tissue. Cardiac muscle tissue is a special type of muscle found only in the heart (Figure 3). All of the cardiac muscle tissue in each part of the heart contracts at the same time. This makes the heart contract and moves the blood around the body. Your heart pumps with a regular beat. The frequency of the beat (the heart rate) changes depending on your physical activity and other factors, such as stress, temperature, and your general health. The muscles and nerves are covered by a smooth layer of epithelial tissues. This covering reduces friction and protects the heart from damage when the lungs expand and contract. The inner surface of the heart, where the blood flows, is also lined with smooth epithelial tissue to allow the blood to flow freely. Any hardening or roughening of this inner lining can lead to health problems. Blood Vessels Three types of blood vessels form a network of tubes throughout the body to transport the blood. These three types of blood vessels are arteries, veins, and capillaries. Arteries carry blood away from the heart. Because the blood in the arteries is being pumped away from the heart, it is under greater pressure than the blood in other blood vessels. The walls of arteries are thicker than the walls of other blood vessels to withstand this pressure. Veins carry blood toward the heart. This blood is at lower pressure, so the walls of the veins are not as thick. Both arteries and veins can vary considerably in size. The largest are nearest the heart, where just a few blood vessels carry large volumes of blood. Further from the heart, the blood vessels are much smaller, and there are more of them, like twigs on a tree. Arteries and veins are linked together by the capillaries (Figure 4). Capillaries are tiny blood vessels with very thin walls that allow substances to diffuse between the blood and other body fluids and tissues. Oxygen and nutrients diffuse from the blood into the surrounding tissues. Carbon dioxide and other wastes pass from the body tissues into the blood to be carried away for disposal. Every part of the body is supplied with blood by a network of capillaries. Figure 3 In this photo of healthy cardiac tissue, the fi bres of cardiac muscle are stained pink. Their nuclei are purple. Figure 4 Capillaries can be so narrow that red blood cells can only pass through one at a time. 84 Chapter 3 Animal Systems

TRY THIS SKILLS: Performing, Observing, Communicating EXAMInIng BLOOD VESSELS Arteries, veins, and capillaries are all blood vessels, but they have very different functions.

Equipment and Materials: microscope; lens paper; prepared slides of cross-sections through arteries, veins, and capillaries SKILLS HANDBOOK 2.D., 3.B.6. 1.

3 TRY THIS SKILLS: Performing, Observing, Communicating EXAMInIng BLOOD VESSELS Arteries, veins, and capillaries are all blood vessels, but they have very different functions. In this activity, you will look at their structures and see how the structure is related to the function. Equipment and Materials: microscope; lens paper; prepared slides of cross-sections through arteries, veins, and capillaries SKILLS HANDBOOK 2.D., 3.B Use your microscope to examine the slide showing an artery. Draw a diagram to illustrate what you see. 2. Repeat Step 1 with the other two slides. A. How are the different functions of the three blood vessels refl ected in their structures? T/I Diseases and Disorders of the Circulatory System There are many conditions that affect the function of the circulatory system. There are over a dozen types of heart disease alone that can affect people of all ages and all levels of fitness. The most common heart problems is coronary artery disease, which can lead to heart attack. Coronary Artery Disease Your heart is a hard-working organ, and the cardiac muscle tissue needs a steady supply of oxygen and nutrients. Coronary arteries are the blood vessels that provide blood to the heart muscle tissue itself. These arteries can become partially blocked with plaque a deposit made of fat, cholesterol, calcium, and other substances that normally circulate in the blood. This plaque buildup can be caused by inherited genetic information or by poor lifestyle choices, such as a high-fat diet, smoking, and lack of exercise. Symptoms of coronary artery disease include tiredness, dizziness, and pain or a burning sensation in the chest or arms. The problem can be diagnosed with the aid of a special X-ray called an angiogram, in which a fluorescent dye is injected into the bloodstream. This dye shows up on the X-ray image (Figure 5). WRITIng Tip Describing Observations Use a thesaurus to fi nd words that describe your observations as specifi cally and accurately as possible. Use words that help readers visualize your observations clearly. By using concrete nouns, adjectives, verbs, and adverbs, your description will give readers a clear picture of what you saw. Figure 5 During an angiogram, a fl uorescent dye is injected into the artery and X-ray scans are taken. This X-ray image has been colourized by a computer. A white rectangle highlights the blockage in the artery in a patient s heart. 3.4 The Circulatory System 85

DID YOU KNOW? Blood Clotting It is important that blood forms clots when the blood vessels are damaged by a cut or scrape.

electrocardiogram (ECG) a diagnostic test that measures the electrical activity pattern of the heart through its beat cycle Heart Attack Coronary arteries can become completely blocked, either with

General symptoms of a possible heart attack include chest pain or pressure shortness of breath nausea anxiety upper body pain abdominal or stomach pain sweating dizziness unusual fatigue The actual

4 DID YOU KNOW? Blood Clotting It is important that blood forms clots when the blood vessels are damaged by a cut or scrape. Some people have disorders that cause the blood to clot too easily, causing blockages, or not quickly enough, so they bleed uncontrollably. Both problems can be life-threatening. electrocardiogram (ECG) a diagnostic test that measures the electrical activity pattern of the heart through its beat cycle Heart Attack Coronary arteries can become completely blocked, either with plaque or with a blood clot. When this happens, the heart muscle cells no longer receive the oxygen and nutrients they need to function. The heart stops pumping, and the heart tissue starts to die. General symptoms of a possible heart attack include chest pain or pressure shortness of breath nausea anxiety upper body pain abdominal or stomach pain sweating dizziness unusual fatigue The actual symptoms of a heart attack can vary widely between men and women and from person to person, but any suspicion of a heart attack requires immediate medical attention. A heart attack can be diagnosed with a blood test and an electrocardiogram. The blood test identifies certain proteins that are present only when cardiac muscle tissue dies. The electrocardiogram (or ECG) measures the electrical signals created by the heart as it beats (Figure 6). The electrical signals from damaged heart muscle tissue are not the same as those from healthy heart muscle. Figure 6 A patient having an electrocardiogram. The blue and white circles are electrodes placed on the skin. These electrodes detect electrical signals. (a) (b) 86 Chapter 3 Animal Systems

RESEARCH THIS SKILLS: Researching, Analyzing the Issue, Communicating The circulatory system is vitally important to our health.

Chose one specifi c disease or disorder of the circulatory system to research, such as coronary artery disease, heart attack, stroke, deep vein thrombosis, or anemia. 2. Research your chosen disease.

PROBLEMS In THE CIRCULATORY SYSTEM SKILLS HANDBOOK 4.A., 4.B. A. Think about how life would change for someone who discovers that he or she has this problem. Write a list of probable life changes.

5 RESEARCH THIS SKILLS: Researching, Analyzing the Issue, Communicating The circulatory system is vitally important to our health. Blockages and other problems can occur in blood vessels in many parts of the body. 1. Chose one specifi c disease or disorder of the circulatory system to research, such as coronary artery disease, heart attack, stroke, deep vein thrombosis, or anemia. 2. Research your chosen disease. Find out the causes, symptoms, diagnostic technologies, treatment, and long-term effects. If you have time, you could also look at the social and economic impacts of your chosen disease. PROBLEMS In THE CIRCULATORY SYSTEM SKILLS HANDBOOK 4.A., 4.B. A. Think about how life would change for someone who discovers that he or she has this problem. Write a list of probable life changes. T/I A B. Summarize your fi ndings in an illustrated presentation or as a short dramatic performance. T/I C C. As a class, discuss whether there are any drawbacks to the use of medical technologies. How expensive are they? Are they readily available to everybody? C A UNIT TASK Bookmark How could you use information about the symptoms of heart disease as you work on the Unit Task on page 156? In SUMMARY The circulatory system is an organ system made up of the blood, the heart, and the blood vessels. The function of the circulatory system is to move nutrients and gases to all of the cells of the body and to carry away wastes through the bloodstream. Heart disease is a group of conditions that affect the function of the heart. Angiograms and electrocardiograms are two medical technologies that are used to help diagnose abnormalities in the circulatory system. CHECK YOUR LEARnIng 1. Describe the function of the circulatory system. K/U 2. Name at least four substances that are carried by the circulatory system. K/U 3. Explain how the circulatory system interacts with the digestive system. K/U 4. How does an angiogram differ from a regular X-ray scan? K/U 5. Figure 7 shows cross-sections of three different blood vessels. Name each one and describe how its structure matches its function. K/U 6. Create a table that lists the main parts of the circulatory system and the tissue types in each part. K/U C 7. (a) Create a pie chart to illustrate the volumes of the various components of blood. (b) What challenges did you face when creating your chart? K/U C 8. How is cardiac muscle different from the smooth muscle that surrounds the digestive tract? K/U 9. Name and briefl y describe two diseases or disorders of the circulatory system. K/U Figure 7 (a) (b) (c) 3.4 The Circulatory System 87

Unit 23.1: The Circulatory System

Unit 23.1: The Circulatory System This color-enhanced image was made with an electron microscope, so the objects it depicts are extremely small. Do you know what they are? This incredible photo shows red