The human body is like a wonderful machine that can carry out amazing

Transcription

1 The human body is like a wonderful machine that can carry out amazing feats. These acrobats use many parts of this machine, such as muscles and bones, to help them balance as they move through hoops above the stage. They train for a long time to be able to control their movements so exactly. There are other parts of the human body that work together without such conscious control. We continually breathe, our hearts beat, and our nerves monitor our environment to protect us from danger. From time to time we are aware of these actions taking place in our bodies. We say things like, I m out of breath, My heart is pounding, or I m scared. Our bodies also perform a variety of other functions that we do not control, such as digesting our food, monitoring our blood sugar levels, and fighting off viruses and bacteria. These important activities are all part of the constant work going on inside the human body to keep it healthy. 52 MHR Unit 1 Cells and Systems

2 2.1 Body Systems A system is made of parts that work together as a whole. In the human body, many different systems work independently, but are also connected to each other. Each organ system consists of organs that are made from various types of tissue. Tissue refers to a group of similar cells working together to carry out a specific function. Key Terms organ organ system tissue Have you ever walked into a bicycle repair shop like the one in Figure 2.1 and noticed all the bike parts, such as wheels, chains, cables, and brake pads? To understand what these parts do, it is helpful to think of the systems that make up a bicycle, such as the gear system and the brake system. It is the parts of these systems working together that make the bicycle an efficient machine. Figure 2.1 The efficiency of a bicycle depends on how well the individual parts of its systems work together to make the bicycle move. The Characteristics of Systems All systems have the following characteristics: 1. A system is made of individual parts that work together as a whole. 2. A system is usually connected to one or more systems. 3. If one part of a system is missing or damaged, the system will not function well or may not function at all. The idea of a system is probably not new to you. Think of the human-made computer system you use and the electrical system that powers it. Scientists use the system idea to study natural systems, too, such the solar system or an ecosystem. For example, scientists study the interaction of living things and non-living things within ecosystems (see Figure 2.2 on the next page). 54 MHR Unit 1 Cells and Systems

3 Your body has a variety of systems that work together to maintain your health. For example, your digestive system converts the food you eat into energy that is used when you carry out your daily activities, and your excretory system removes the waste from that process. Connection Section 12.1 has more information about pond ecosystems. Did You Know? Aristotle, who lived from 384 to 322 B.C.E., was a great philosopher. He also closely observed natural objects and events. He dissected animals to compare their body systems, a form of scientific inquiry that became known as comparative anatomy. Historians believe he made such studies to develop hypotheses about how human body systems might work. Figure 2.2 Living things (such as turtles) interact with non-living components (such as water and rocks) in this pond. 2-1 Your Body Systems Find Out ACTIVITY In this activity, you will illustrate what you already understand about the parts of your body and your own body systems. What to Do 1. Work with a partner. On a large sheet of paper, trace the outline of your partner s body. When drawing your line leave enough space so you do not mark your partner s clothes. Make sure the paper is big enough so that you can outline the entire body. 2. Sketch and label all the different body parts and body systems you know on the drawing your partner has made of your body. 3. Keep your drawing. As you work through this chapter, refer back to it and add any new information you learn. What Did You Find Out? 1. Compare your work with your partner s. Make a list for each question below. (a) Which body parts and systems did you both identify? (b) Which body parts and systems did your partner identify that were different from the ones you identified? (c) Share your list and discuss with your class the different body parts and systems that were identified. Chapter 2 Human body systems work independently and together. MHR 55

4 Introducing the Systems of the Human Body Figure 2.3 Eleven systems of the human body Circulatory System Transports blood, nutrients (chemicals needed for survival), gases, and wastes. internet connect Digestive System Takes in food. Breaks down food. Absorbs nutrients. Eliminates solid waste. To see an interactive, threedimensional body, go to Respiratory System Controls breathing. Exchanges gases in lungs and tissues. Excretory System Removes liquid and gas wastes from the body. Immune System Defends the body against infections. 56 MHR Unit 1 Cells and Systems

5 Endocrine System LEFT: Manufactures and releases hormones. Reproductive System RIGHT: Includes reproductive organs for producing offspring. Integumentary System Includes skin, hair, and nails. Creates a waterproof protective barrier around the body. Skeletal System Supports, protects, and works with muscles to move parts of the body. Muscular System Has muscles that work with the bones to move parts of the body. Nervous System Detects changes in the environment and signals these changes to the body, which then carries out a response. Chapter 2 Human body systems work independently and together. MHR 57

6 Did You Know? There are different types of cells in your heart. One unique type of cell is called a myocyte. (In Greek, myo means muscle, and cyte means cell.) This cell can do something no other cell can do. It can beat on its own just like a tiny heart. When a group of myocytes are close together, they send chemical signals back and forth, which cause them to beat together at the same time. Organ Systems: Putting It All Together In Figure 2.3 on pages 56 57, you can see 11 different body systems. Each body system is called an organ system. An organ system has one or more organs that perform specific body functions. For example, your heart is part of the circulatory system. You may recall that the heart pumps blood to the lungs and out into the rest of your body. Within each organ system are tissues and cells. Cells of the same structure and function are grouped into tissues. Groups of tissues form organs, such as the lungs or the heart. For example, heart cells work together to form heart tissue. Several types of heart tissue work together to form the organ you call your heart. Figure 2.4 shows the relationship between cells, tissues, organs, and organ systems. Tissues: The Foundation of Body Systems The word tissue comes from a Latin word meaning to weave. The cells that make up tissues are often woven, or held together by fibres or sticky materials that form between tissue cells. Table 2.1 on the next page describes how each type of tissue works in your body. These four types of tissue form the basis for all organs in your body. heart cell cardiac tissue organ (heart) organ system organism (circulatory system) Figure 2.4 The cell is the basic unit of life. Cells working together make up tissue. An organ consists of several types of tissues working together to perform a task, such as the pumping of blood by your heart. Organs working together make up an organ system. 58 MHR Unit 1 Cells and Systems

7 Table 2.1 How Tissues Function in the Human Body Muscle tissue, such as skeletal muscle tissue, assists in body movement. It also helps some organs carry out specific functions, such as the heart pumping blood. Nerve tissue transfers signals in the body and its organs to tell the body how to respond to changes in its internal and external environments. Connective tissue holds together and supports other tissues, such as skeletal connective tissue. Connective tissue connects, protects, and insulates organs. Epithelial tissue covers the surface of organs and the body. It also lines the inside of body parts, such as the mouth, esophagus (shown here), and the stomach. Select one of the systems from Figure 2.3 on pages Research and describe the characteristics of the main structures and their functions. Explain how this system interacts with at least one other system. Begin your research at Modelling Four Types of Tissue Think About It Imagine that your group has been asked by a local doctor s office to make a model of each type of body tissue. The models will form part of an exhibit on the human body. In this activity, your group will determine which material will make the best model of each tissue. What to Do 1. Your teacher will give your group the following four materials. rubber band piece of plastic wrap electrical wire transparent adhesive tape 2. Using the information on tissues in Table 2.1, determine which material best models one of the four types of tissue. Develop a chart to compare the material to the type of tissue. What Did You Find Out? 1. Compare your chart with other groups in your class. Be prepared to defend your answers if there is a disagreement between groups. 2. Explain in a paragraph how another material could be used to model one of the four types of tissue. Science Skills Go to Science Skill 8 for information about using models in science. Chapter 2 Human body systems work independently and together. MHR 59

8 Checking Concepts 1. What are the three characteristics of a system? 2. How is a bicycle an example of a humanmade system? 3. Which body system removes liquid and gas wastes from the body? 4. Which system does the heart belong to? 5. Which system controls breathing? 6. Which system defends the body against infection? 7. Match the following four images of tissue to the correct function. A B Understanding Key Ideas 11. Think of a human-made system not discussed in this textbook or class. Describe this system and explain how the three characteristics of a system are represented in your example. 12. Give an example of how two body systems interconnect or rely on each other to function. 13. Multiple sclerosis (MS) is a disease that causes the breakdown of tissue in the central nervous system. Which types of tissue are affected by MS? 14. Select one graphic organizer described in Science Skill 10 and use this organizer to explain the bolded terms in this section. Pause and Reflect C (a) holds together and supports other tissues (b) transfers signals in the body (c) covers the surface of the body (d) assists in body movement 8. If you were given a copper wire from an extension cord and asked which type of tissue this cord best modelled, what would be your answer? Explain. 9. What is the difference between an organ and a tissue? 10. Explain the four levels of organization within the human body. D Figure 2.3 on pages shows 11 different body systems. If one of these systems no longer functioned, what would be the impact on the rest of the body? Explain your answer in a paragraph. Chapter 2 Human body systems work independently and together. MHR 63

9 2.2 The Digestive and Excretory Systems A healthy body requires nutrients from five groups: carbohydrates, proteins, fats, vitamins, and minerals. There are four stages in digestion: ingesting, digesting, absorbing, and eliminating. The digestive system is basically a long tube along which organs perform different functions as the nutrients pass through them. The excretory system removes liquid and gas wastes from your body. In this system, the process of excretion removes the liquid wastes through the urinary tract. Eating disorders have a negative effect on how the digestive system functions. Key Terms digestion excretion gastric juice mucus nutrients villi At birth, the average baby has a body mass of 3 to 4 kg. By age 14, a teenager s body mass has increased at least 10 times or more. How did this happen? To grow, your body needs raw materials or nutrients (see Figure 2.5). Nutrients are substances the body requires for energy, growth, development, repair, or maintenance. We get nutrients from what we eat and drink, which health professionals call our diet. You probably think that diet means to cut out foods so you can use lose weight. But the word diet actually refers to the amount and type of food you should eat to maintain your health. food provides nutrients in the form of Did You Know? A blue whale eats for only four months of the year. During this time, it will eat 4000 kg of plankton a day. carbohydrates, fats, proteins, vitamins, and minerals Figure 2.5 We need to eat foods that will provide us with the nutrients our bodies need to stay healthy. which provide energy and materials used for growth, development, and repair 64 MHR Unit 1 Cells and Systems

10 2-4 Using Canada s Food Guide to Find Out ACTIVITY Healthy Eating How do you know what kinds of food to eat to make sure your body is getting the nutrients it needs? One way is to follow the suggestions in Canada s Food Guide to Healthy Eating. In this activity, you will use this guide to help you become an informed food shopper. What to Do 1. Your teacher will give you a copy of Canada s Food Guide. Prepare a shopping list of foods you would need to purchase to have three meals and two snacks for one day. (Assume the store you shop at has all the food packaged into single servings.) You may also use other information from this textbook and any additional print and electronic resources available to you. What Did You Find Out? 1. Compare your list with your classmates lists. 2. Make a second list of all the foods you ate yesterday. Compare this list with your shopping list and answer the following questions. (a) For which food groups did you have the appropriate number of suggested servings? (b) For which food groups did you not have the appropriate number of suggested servings? (c) What foods should you eat more of? 3. What is one food you enjoy that is not on your list of foods to buy? Could you live without this food? Types of Nutrients A balanced diet ensures that you take in the correct amount of nutrients your body needs to function. There are five different types of nutrients you can obtain from food. These are carbohydrates, proteins, fats, minerals, and vitamins. internet connect For more examples of food guides from various countries and cultures go to Carbohydrates Carbohydrates are the body s quickest source of energy. There are two types of carbohydrates: simple and complex. A simple carbohydrate is a molecule of a sugar. The most common type of sugar is glucose. You can think of glucose as fuel for your body. Recall that the mitochondria in your body cells change glucose into energy through the process of cellular respiration. Your body uses this energy for growth, repair, and maintenance. A complex carbohydrate is a chain of simple carbohydrates (sugar molecules) joined together. Foods such as pasta, brown rice, and whole grain cereals contain complex carbohydrates (see Figure 2.9 on the next page). When you eat a food containing complex carbohydrates, your body needs to break down the chain into simple sugars before it can use the energy. This process takes time, and in the long term is one of the reasons eating complex carbohydrates is better for you than eating a diet high in simple sugars. Eating sweet foods may make you want to eat more or make you hungry again just a short time later. 66 MHR Unit 1 Cells and Systems

11 Proteins Proteins are used to build parts of your body s muscles, skin, hair, and nails. Your body also manufactures proteins for use in various chemical reactions within your cells. Foods such as fish, poultry, nuts, soy, and dairy products are rich in proteins (see Figure 2.8). Fats Fats are used to build cell membranes and can be stored by the body for future energy uses. Foods such as shortening, butter, oil, cream, and meat contain fat (see Figure 2.10). Currently, many people consume food with too much fat. Dietitians and doctors recommend that Canadians reduce the total amount of fat in their diets. You may have heard on the news or read in a magazine about good and bad fat. Good fat is sometimes called unsaturated fat and comes from fruits, vegetables, and fish. Corn oil, olive oil, and vegetable oil are also examples of unsaturated fats. These fats are liquid at room temperature. Animal fats, such as butter or lard, are saturated fats. These fats are solid at room temperature. Figure 2.8 Proteins are in foods such as fish, meat, poultry, eggs, nuts, and soy products. Figure 2.9 Carbohydrates are in foods such as rice, vegetables, cereal, and bread. Figure 2.10 Fats are in foods such as butter, vegetable oil, and meat. Research shows that diets rich in saturated fat can lead to an increase in heart disease. Scientists think that saturated fats promote the build-up of a material called plaque. Plaque is a fatty material that is deposited along the walls of blood vessels. As plaque builds up in the blood vessels, the flow of blood through the heart and body is reduced. This leads to an increased risk of heart attacks and strokes. Chapter 2 Human body systems work independently and together. MHR 67

12 Minerals and vitamins Minerals and vitamins are needed by the body in small amounts to perform various body functions. Figure 2.11 shows some of these minerals. Two common minerals and vitamins are calcium and vitamin D. Calcium is required to help build strong bones. A lack of calcium can lead to osteoporosis, which is a disease that weakens your bones. Vitamin D is required by your body to assist it in absorbing calcium. Fluorine (F) Function: Dental cavity reduction Source: Fluoridated water Iron (Fe) Function: Formation of red blood cell parts; transportation of oxygen throughout the body Source: Liver, egg yolks, grains, meats, leafy vegetables Calcium (Ca) Function: Teeth and bone formation; muscle and nerve activity Source: Milk, grains, calcium-fortified orange juice and soy milk Phosphorus (P) Function: Teeth and bone formation; muscle and nerve activity Source: Milk, grains, vegetables Sodium (Na) Function: Nerve activity Source: Bacon, butter, table salt, vegetables Magnesium (Mg) Function: Muscle and nerve activity; bone formation Source: Fruits, vegetables, grains Copper (Cu) Function: Development of red blood cells Source: Grains, liver Potassium (K) Function: Muscle and nerve activity Source: Vegetables, bananas Sulfur (S) Function: Hair, nails, and skin builder Source: Grains, fruits, eggs, cheese Figure 2.11 Minerals perform many different functions in the body. 68 MHR Unit 1 Cells and Systems

13 A person who lacks vitamin D can develop rickets, which causes the bones to weaken. Fortunately, one way you can help your body make vitamin D is by simply going outside in the sunlight. However, it is difficult for some people to get enough sunlight. For example, if you live above 52 north latitude, there is not enough sunlight to make vitamin D between the months of October and March. Drinking beverages with added vitamin D, such as milk and soy milk, can help you get the vitamin D you need. Water Water is not a nutrient, but it is necessary for life. Water transports nutrients and wastes. It is also necessary for many chemical reactions and for cooling the body through perspiration or sweat. Your body requires 3 to 5 L of water each day. Table 2.2 summarizes the nutrients you have just read about and describes some of their functions in your body. internet connect Go to for more examples of minerals and vitamins and how they function in the human body. Table 2.2 How Nutrients Function in the Human Body Nutrient Carbohydrates Proteins Fats Minerals and vitamins Function Are the body s quickest source of energy. Carbohydrates come in simple and complex forms. Complex carbohydrates are chains of simple carbohydrates (sugar molecules). Are used to build parts of the body, such as muscles, skin, and hair, and are also used for various chemical reactions in your body. Can be stored by the body for future energy use. Are both needed in small amounts to help your body perform various functions, such as building bone strength. Reading Check 1. Explain one way to determine if you are eating a healthy diet. 2. What is the difference between a simple carbohydrate and a complex carbohydrate? 3. What are two functions of proteins? 4. Give a food example for each of the five nutrients. 5. What is the role of water? 6. State one function of fluorine. 7. State two sources of potassium. Chapter 2 Human body systems work independently and together. MHR 69

14 The Four Stages of Digestion You can put any food into your mouth, and your body will be able to break down, absorb, and store its nutrients. Any food your body cannot use will be eliminated. This process is called digestion, and it occurs in an amazing system called the digestive system (see Figure 2.12). Digestion takes place in four stages: ingesting absorbing digesting eliminating ingesting salivary glands esophagus tongue digesting liver stomach pancreas absorbing eliminating gall bladder large intestine anus small intestine rectum Figure 2.12 The four stages of digestion in the digestive system Word Connect In scientific terms, to ingest means to take in. To digest means to break down. Enzymes are important proteins for digestion In your body, many different chemical reactions are occurring. Many of these reactions could not normally occur at body temperature because they would happen very slowly. An enzyme is a protein found in your body that helps speeds up these reactions. There are many different types of enzymes in your body. During the digestion process, one enzyme or more will be present in each organ. 70 MHR Unit 1 Cells and Systems Digestion occurs along a big tube This may sound strange, but your digestive system is basically one big tube that starts at your mouth and ends at your anus. The shape of the tube changes along its length, getting bigger in some places and smaller in others. The process of digestion breaks down your food into small pieces so that the nutrients can be absorbed into your body and used for maintenance, growth, and repair. Any materials that cannot be absorbed are eliminated in the feces.

15 To get a better idea of how digestion works, imagine the journey of a favourite food through the four stages of the digestion process. As you read, make an illustration or look back at your body diagram from section 2.1, and record the names of the different body structures and organs that carry out the digestion process. Stage 1: Ingesting Ingesting, or ingestion, is the starting point of the digestion process. Figure 2.13 shows that this process begins when you bite off a piece of apple or take a sip of milk. Stage 2: Digesting You start digesting your food the moment you start chewing. This process involves several body structures along the digestive tube. Mouth When food enters your mouth, it undergoes both mechanical and chemical digestion. Mechanical digestion occurs when you use your teeth and tongue to chew food into pieces small enough for you to swallow. Each small piece of food is called a bolus. Before you swallow the bolus, it is covered in saliva, which helps it continue its journey down the digestive tube. Saliva is produced from salivary glands in your mouth. Saliva also contains an enzyme, called amylase. Chemical digestion occurs when amylase begins to break down the food bolus by breaking down complex carbohydrates into simple carbohydrates. Figure 2.14 shows the tongue and other structures of the mouth. Figure 2.13 Ingestion begins with your first bite of food. Suggested Activity Conduct an Investigation 2-5 on page 78 Teeth The incisors are adapted for cutting food. The cuspids, or canines, tear or shred food. The three sets of molars can crush and grind food. Tongue The tongue is attached to the floor of the mouth. It is made of numerous skeletal muscles covered with a mucous membrane. molars incisors Tonsils A pair of tonsils is located at the back of the mouth. They play a role in preventing infections in the nose and mouth by helping to eliminate foreign bacteria. Did You Know? Salivary glands produce about 1 L of saliva a day. bicuspids or premolars The tongue is covered by projections. Figure 2.14 The mouth cuspids or canines opening of a salivary gland duct Chapter 2 Human body systems work independently and together. MHR 71

16 airway tube epiglottis Figure 2.15 The epiglottis covers the airway tube and prevents food from entering. Esophagus As the food moves from your mouth, it passes through the pharynx. The pharynx is where your airway passage and the rest of your digestive system meet. Imagine two tubes coming together and joining into one. Since each tube has a different function, one for breathing and one for digesting food, your body has a simple but effective way of keeping the two tubes separate. A small flap of flesh, called the epiglottis, covers the airway tube (see Figure 2.15). When you swallow, the flap covers the airway and your food carries on to the esophagus. The esophagus is the part of the digestive tube that connects the pharynx and stomach. If you have ever choked on some food or a drink, your epiglottis has opened up, and the food or liquid has gone down your airway passage instead of your esophagus. The esophagus is long and muscular. The bolus is pushed through the esophagus in a process called peristalsis (see Figure 2.16). The process of peristalsis is like using your hands to squeeze a marble down through a small rubber tube. The action of your hands squeezing the tube is like the muscles of the esophagus pushing each bolus to the stomach. Figure 2.16 Peristalsis is a series of muscle contractions that move food through the digestive system. from mouth bolus to stomach muscle muscle A contraction contraction of muscles behind bolus B contraction of muscles ahead of bolus C contraction in muscles forces the bolus forward D 72 MHR Unit 1 Cells and Systems

17 Stomach Your stomach is like a stretchable muscular bag. In fact, your stomach can stretch to hold about 2 L of food or liquid. Inside the stomach is gastric juice, which is made from hydrochloric acid, mucus, and enzymes and is secreted by your stomach s lining. Gastric juice is very acidic and the stomach walls are lined with mucus that protects the tissue from being damaged by the acid. One of the reasons the gastric juice must be acidic is that the enzyme pepsin, which breaks down protein, needs an acidic environment in which to function. As each bolus drops into the stomach, it is covered by gastric juice and is slowly mixed around by the contractions of the stomach muscles. The bolus breaks down into a liquid called chyme (see Figure 2.17). This process can take from two to six hours. In Figure 2.18, you can see a sphincter at each end of the stomach. Sphincters are found throughout the body and are round muscles that, when open, allow materials to move through them. In your stomach, there are two sphincters. The first is between the esophagus and the stomach, and it regulates the entry of each bolus into the stomach. When a person vomits or has heartburn, the flow of material is reversed, and gastric juice and partially broken-down food moves back up the esophagus. Any burning sensation the person feels in the throat or mouth is because of the hydrochloric acid in the gastric juice. The second sphincter regulates the flow of chyme out of the stomach and into the small intestine. small intestine esophagus stomach Figure 2.17 Muscle contractions churn the stomach s contents until it becomes a thin liquid called chyme. chyme esophagus duodenum entrance to stomach stomach Figure 2.18 A sphincter at the entrance to the stomach controls the entry of food from the esophagus. A sphincter at the end of the stomach controls the flow of chyme into the small intestine. end of stomach Chapter 2 Human body systems work independently and together. MHR 73

18 Small intestine Once the liquid chyme leaves the stomach, it empties into the small intestine. This organ is a tube about 6 m long and 2.5 cm in diameter. The first metre of the small intestine is called the duodenum. The second stage of the digestion process is complete once the food particles leave the duodenum. More about chemical digestion in the small intestine Within the first 30 cm of the small intestine are ducts or tubes that connect to other organs, such as the pancreas, liver, and gall bladder (see Figure 2.19). esophagus liver Figure 2.19 Both the liver and pancreas produce chemicals needed for digestion in the small intestine. gall bladder stomach bile duct duodenum pancreas pancreatic duct small intestine Using print and electronic resources, research a different animal s digestive system. Focus on different organs and structures that may be present. For example, why do some birds have gizzards or cows have four stomachs? Begin your research at The pancreas is a small organ that produces digestive enzymes that pass into the small intestine. These enzymes help in the further breakdown of the carbohydrates, protein, and fat in the chyme. The liver produces a substance called bile. Bile is stored in the gall bladder. The function of bile is to break the globs of fat into smaller droplets, similar to how dish detergent breaks up grease. This process helps the pancreatic enzymes break down the fat into even smaller particles. Stage 3: Absorbing Now the nutrients are ready to be absorbed by the remaining 5 m of the small intestine. This process is called absorption. 74 MHR Unit 1 Cells and Systems

19 Small intestine To help increase the rate of absorption of nutrients into your body, the small intestine is covered in villi (singular: villus). Villi are structures that look like folds in the wall of the small intestine (see Figure 2.20). Each of these folds increases the surface area available to take in nutrients. In fact, if you were to calculate the total surface area of the small intestine, you would find that it takes up an area about the size of a tennis court, or about 250 m 2. If the small intestine did not have villi, the total surface area would be only about 0.5 m 2, which would make absorption difficult. Food, typically, takes five to six hours to pass through the small intestine by peristalsis. small intestine magnification: 360 villi Figure 2.20 The small intestine with magnified villi close-up of villus magnified villi Large intestine Your large intestine is 5 cm wide and 1.5 m long. Its main function is to take undigested material from the small intestine and reabsorb the water and some minerals. Peristalsis continues to move the undigested food along the digestive tube. By the time the undigested material leaves your large intestine, 90 percent of the water that entered your small intestine has been reabsorbed. This process takes about 12 to 24 hours. The role of bacteria in digestion Many different types of bacteria live in your digestive system. Beneficial bacteria assist in the breakdown and absorption of food. For example, bacteria in the large intestine use undigested material to make vitamins, such as vitamin K. Vitamin K helps your blood to clot. At birth, babies do not yet have bacteria in their digestive system. Doctors will give them a shot of vitamin K to last until they have enough bacteria to begin producing it. Sometimes we ingest bacteria that are not beneficial, such as salmonella, which cause food poisoning. Did You Know? For many years, scientists thought that stomach and intestinal ulcers were caused by stress and lifestyle. But current scientific research has discovered that some ulcers are holes in the lining of the stomach and intestines caused by the bacterium Helicobacter pylori. This discovery by two Australian scientists, Robin Warren and Barry Marshall, won them the Nobel Prize for medicine in Chapter 2 Human body systems work independently and together. MHR 75

20 Stage 4: Eliminating Any undigested materials left at this point in the digestion process are called feces. Feces are the solid waste products of the digestion process and are stored in the rectum until they are eliminated through the anus. This stage is called elimination, which is the end of the digestion process. The whole process, from ingesting food to eliminating waste, takes approximately 20 to 30 hours. Other organs of the excretory system include the lungs, the skin, and the liver. What roles do these organs play in removing wastes from your body? Begin your research at Excretion In Figure 2.3 on pages 56 57, you learned that your excretory system removes liquid and gas wastes from your body. In this system, the process of excretion removes the liquid wastes through the urinary tract. The main organs involved are your two kidneys, two tubes that carry urine called the ureters, the bladder, and the urethra (see Figure 2.21). The kidneys filter blood and remove any wastes. As the blood is filtered, urine is formed and passed down the ureters to the bladder where it is stored. When the bladder is full, the urine is flushed from the body through the urethra. vena cava bladder aorta kidney ureters urethra Figure 2.21 The kidneys, ureters, bladder, and urethra are the main organs involved in excretion. Reading Check 1. Which organs and structures carry out digestion? 2. What is a bolus? 3. Describe the function of an enzyme and give an example. 4. What is the function of a mucous coating on the stomach wall? 5. How is the surface area of the small intestine increased? 6. What is the main function of the large intestine? 76 MHR Unit 1 Cells and Systems

21 Nutritional Disorders Disrupting the Digestive System Obesity is an excess in body fat. In Canadian teenagers, obesity is quickly becoming a serious health concern. Research has shown that the number of obese teenagers tripled between 1981 and Lack of exercise and improper eating habits are increasing the number of people who are obese. Most cases of obesity result from taking in more food than the body requires. Potential negative health effects of obesity include an increased risk of diabetes, heart disease, stroke, and asthma. Eating Disorders Eating disorders occur when a person does not get the required nutrients to be healthy. Two examples of eating disorders are anorexia nervosa and bulimia nervosa (see Table 2.3). Anorexia nervosa is a disorder that occurs when a person severely restricts what she or he eats. The resulting medical problems could include damage to internal organs and weakening of bones. Bulimia nervosa is a disorder that occurs when a person eats large amounts of food and then vomits or takes laxatives to get rid of the food before it can be completely digested. This eating disorder can cause a variety of health problems, including stomach and esophagus irritation and tooth decay from stomach acid in the vomit. internet connect For more information on eating disorders, go to Table 2.3 Characteristics of Anorexia Nervosa and Bulimia Nervosa People with anorexia nervosa: are very afraid of gaining body mass limit the amount of food they eat very strictly have a distorted body image, which means they feel overweight even when they are dangerously thin have a body mass that is less than 85 percent of normal body mass do not menstruate (female anorexics) People with anorexia nervosa keep their body mass low by: eating very little or eating foods extremely low in calories exercising too much misusing laxatives People with bulimia nervosa: are very concerned about their body shape and weight repeatedly eat a much higher than normal amount of food at one sitting (binge eating) and feel they are unable to control their eating at these times have a distorted body image, which means they feel overweight even when they are normal have a body mass that is normal or less than normal often have bad breath and gum disease People with bulimia nervosa keep their body mass low by: making themselves vomit (purging) after eating exercising too much misusing laxatives Chapter 2 Human body systems work independently and together. MHR 77

22 Checking Concepts 1. List the food groups in Canada s Food Guide to Healthy Eating and give an example for each group. 2. List each type of nutrient and describe its function. 3. What is the role of the epiglottis? 4. In humans, where does most of the chemical digestion process occur? 5. Why does your stomach need to be very acidic? 6. Order the following structures in the correct sequence from ingestion to elimination: rectum stomach esophagus duodenum mouth small intestine anus large intestine 7. In which organ is water absorbed? 8. What other organs outside the digestive tube contribute to digestion? 9. Describe one of the beneficial roles of bacteria in the digestive system. 10. Why are eating disorders harmful to the human body? 11. Copy the following concept map into your notebook and fill in the blanks. Digestion Understanding Key Ideas 12. What foods from the four food groups or the food pyramid would provide a balanced meal? Explain. 13. Compare and contrast mechanical digestion and chemical digestion. 14. Explain how the digestive system can be compared to a big tube. 15. Bread contains complex carbohydrates. If you let a piece of bread sit in your mouth for about five minutes without being chewed, it starts to taste sweet. Explain why this happens. 16. A blue whale eats 4000 kg per day, and a rat eats about 15 g per day. Both animals replace about 5 percent of their body mass each day. What is the approximate mass of both animals? 17. How is the function of bile similar to the function of soap? 18. Explain the relationship for each set of terms below. (a) digestion, enzymes (b) surface area, villi (c) digestion, bacteria (d) esophagus, peristalsis (e) gastric juice, pepsin, mucus (f) kidney, bladder, excretion breaks down starts in to be used by by chewing by enzymes in saliva the food is moved through the system by Pause and Reflect Develop a flowchart showing the organs and structures of the digestive system. Use a different colour for each stage of the digestion process. (You will need four colours.) Recall that some stages overlap. Chapter 2 Human body systems work independently and together. MHR 81

23 2.3 The Circulatory and Respiratory Systems The circulatory system consists of the heart, arteries, capillaries, and veins. Arteries carry blood away from the heart, and veins carry blood to the heart. In your capillaries, oxygen is released into your body and carbon dioxide is collected. In your lungs, oxygen is collected and carbon dioxide is released into the alveoli. Emphysema, which is often caused by smoking, and pneumonia are two examples of respiratory diseases. Key Terms alveoli arteries blood capillaries circulatory system gas exchange respiratory system veins After a run or some other type of exercise, place your hand on your chest. Can you feel your heart beating? For your whole life, this organ continues to beat, moving blood throughout your body. Your heart is a pump that pushes approximately 4 L of blood per minute through your body. If an average heart beats about 70 times per minute, and you live to be 80 years old, that s almost three billion beats. This amazing feat is accomplished by a muscle about the size of your fist. Unlike other organs in your body, your heart is more difficult to take a picture of because of its constant beating. Blockages in the blood vessels of the heart, which can cause heart attacks, are not visible in an X ray. Scientists and physicians continue to search for new ways to make images of the heart to help them diagnose heart problems sooner and prevent the advance of heart disease. One recent technology is the 64-Slice CT Scanner. The scanner takes 64 pictures of different sections of the heart. Each image is very thin. The images are then combined to form the three-dimensional picture you see in Figure The whole process takes place in about five heartbeats. internet connect Go to to observe a heart simulation. Figure 2.22 This picture of the heart was taken by a type of scanner called the 64-Slice CT Scanner. 82 MHR Unit 1 Cells and Systems

24 Suggested Activities Find Out Activity 2-8 on page 93 Taking a Closer Look at the Heart Your heart is a muscular organ that pumps blood throughout your body. Figure 2.23 shows its four chambers: two upper atrium chambers and two lower ventricle chambers. The atria allow the blood to move from the body into the heart. The ventricles pump the blood out of the heart. It may seem backward that the atria are labelled right and left on the diagram. But imagine the heart as it is positioned in your body. The right atrium refers to the right side of your body, not the right side of the diagram. Notice in Figure 2.23 that the muscle around the left ventricle is larger than that around the right ventricle. The left ventricle pumps your blood out to your body. The right ventricle pumps blood to your lungs, a much shorter distance. The walls of the atria are much thinner because they only have to pump the blood a short distance into the ventricles. arteries superior vena cava aorta pulmonary artery Word Connect valve right atrium veins from lung left atrium valve For many scientific words, the plural form is created by adding s or es, to the end of a word. You will find examples of these types of plural words in this chapter, such as veins (singular: vein), arteries (singular: artery), capillaries (singular: capillary). But the plural form of some words is created by adding a different letter. For example, atrium is the singular form, and atria, which refers to more than one atrium, is the plural form. valve right ventricle inferior vena cava valve left ventricle Figure 2.23 The human heart. The arrows show the direction of blood flow through the heart. Between the chambers are valves. Each valve allows blood to flow in only one direction. If you have ever listened to your heart through a stethoscope, the lub dub sound you hear is the opening and closing of the valves. 84 MHR Unit 1 Cells and Systems

25 The Circulatory System The heart is part of the circulatory system, which is like an enormous highway system that moves blood throughout your body. The roads that make up the circulatory system are your blood vessels. Blood moves along these roads from your heart to all parts of your body and back again as in Figure All your blood vessels lined up end to end would be about km in length. That is about 2.5 times around Earth at the equator. veins from the head arteries to the head veins from the arm arteries to the arm veins taking blood to heart right atrium receives blood from body left atrium receives blood from lungs left ventricle pumps blood out to the rest of the body right ventricle pumps blood to lungs artery to kidney vein from kidney arteries to legs veins from legs Figure 2.24 The circulatory system moves blood throughout the body. Chapter 2 Human body systems work independently and together. MHR 85

26 Connection Section 9.3 has more information about blood pressure. Types of Blood Vessels Blood is carried from your heart throughout your body in three types of blood vessels: arteries, capillaries, and veins. Arteries are blood vessels that carry blood away from your heart. Most arteries carry bright red, oxygenated (oxygen-containing) blood. Your blood is under pressure after it is pumped from your heart. The pressure keeps it flowing in one direction. Your arteries are thick-walled and elastic and can withstand this pressurized flow. The largest artery in your body is the aorta. It has a width of about 25 mm or the width of a penny. As blood moves farther away from your heart, your arteries branch into smaller and smaller arteries (see Figure 2.25). Eventually, the smallest arteries, the arterioles, which have a diameter of about 0.5 mm, reach the capillaries. Capillaries are a network of tiny blood vessels that act like a highway interchange. Here oxygen, nutrients, and glucose diffuse through the very thin walls of the capillaries into the fluid that surrounds tissue cells (see Figure 2.26). In exchange, carbon dioxide and other waste materials that have diffused out of these cells diffuse into the capillaries. arteriole capillaries venule blood flow artery blood flow vein Figure 2.25 Arteries carry blood away from the heart to the capillaries. From the capillaries, blood moves through the venules and into the veins back to the heart. Figure 2.26 Disk-shaped red blood cells carry oxygen to tissue cells through the thin-walled capillaries. After leaving the capillaries, your blood no longer contains oxygen. This deoxygenated blood is carried back to your heart through tiny venules and into your veins. Figure 2.23 on page 84 shows blood from the head and body in the superior vena cava and inferior vena cava emptying into the heart. Deoxygenated blood is thicker than oxygenated blood and is much darker in colour. In Figure 2.25, the colour blue is used to show the deoxygenated blood in veins. Once the deoxygenated blood reaches your heart, it is pumped into your lungs, where it becomes oxygenated again. 86 MHR Unit 1 Cells and Systems

27 arteriole venule capillary valve inner layer middle layer outer layer artery vein Figure 2.27 An artery has much thicker walls than a vein. Figure 2.27 shows that veins often have valves that prevent the backflow of blood as it travels back to the heart. They also have thinner walls because the blood travelling back to the heart is not under pressure like the blood in the arteries. 2-7 Visualizing Blood Flow Think About It In this activity, you will create a flowchart to show blood flow in the body. What to Do 1. Copy this flowchart into your notebook. right atrium 2. Starting with the right atrium, place the following structures on the flowchart in the order that blood flows through the body. left ventricle left atrium body lungs right atrium right ventricle 3. Add the following terms to the flowchart. aorta superior vena cava pulmonary vein inferior vena cava pulmonary artery 4. The arrows represent the flow of blood between the structures. In your flowchart, show this by making oxygenated blood red and deoxygenated blood blue. What Did You Find Out? 1. You know that most arteries carry oxygenated blood and are coloured red. You also know that most veins carry deoxygenated blood and are coloured blue. Where in your diagram is there an exception to this statement? Chapter 2 Human body systems work independently and together. MHR 87

28 superior vena cava aorta capillaries pulmonary artery pulmonary vein pulmonary artery left atrium right atrium pulmonary vein right lung inferior vena cava right ventricle left ventricle left lung Figure 2.28 Blood flow through the heart and lungs from a different view Figure 2.28 shows blood flow through the heart and lungs. In this diagram, you can see the blood on the right side of the heart is blue and the blood on the left is red. The deoxygenated blue blood goes out of the heart to the lungs. This is the only artery in the body to carry deoxygenated blood. The only vein to carry oxygenated red blood comes from the lungs back to the left side of the heart. The Components of Blood Blood performs several essential functions necessary for your health. It transports oxygen, nutrients, and water to your cells and carries carbon dioxide and wastes away from your cells. Blood also carries specialized cells to help fight infections and heal wounds. The human body contains about 5 L of blood. About 55 percent of this volume is a liquid called plasma. Plasma is a clear, yellowish fluid that contains numerous proteins, minerals, and other substances. Figure 2.29 on the next page shows some of the important components of plasma. 88 MHR Unit 1 Cells and Systems

29 Plasma (55%) water proteins and minerals dissolved salts Other Components (45%) red blood cells white blood cells platelets Figure 2.29 The components of blood Figure 2.30 Three of the components in blood: red blood cells (red disks), white blood cells (pale purple spheres), and platelets (irregular shapes) Red blood cells, white blood cells, and platelets make up the other 45 percent of blood components (see Figure 2.30). Every second your body produces approximately two million red blood cells. Red blood cells carry oxygen from your lungs to the cells of your body and carbon dioxide from your body cells to your lungs, where it is exhaled. Red blood cells are formed in a fatty tissue called bone marrow. Bone marrow is found inside bone, such as inside the hollow part of your thigh bone. Red blood cells are also produced in the liver and spleen. Within each red blood cell are protein molecules of hemoglobin. This molecule carries oxygen to the capillaries and carbon dioxide to the lungs. White blood cells fight infection and prevent the growth of cancer. They are much larger in size than red blood cells. A drop of healthy blood contains about 5000 to white blood cells. When you get an infection, the number of your white blood cells increases. Platelets are important for clotting blood. When you get a cut, platelets stop the bleeding and seal the wound by thickening the blood so a scab can form over the cut. There are about to platelets in a drop of blood. Did You Know? There are about 25 trillion red blood cells in your body. Reading Check 1. What are the four chambers of the heart? 2. What causes the lub dub sound your heart makes? 3. Explain the difference in structure between arteries and veins. 4. Do all arteries carry oxygenated blood? Explain. 5. What are the components of blood and their functions? Scientists are finding new information about blood cells and their functions. Go to to find out about current research on blood cells. Chapter 2 Human body systems work independently and together. MHR 89

30 Connection Section 9.3 has more information about how air is brought into your lungs. Did You Know? Humans can travel above 8000 m for only a brief period of time without the support of additional oxygen. At this altitude, the air contains very little oxygen. Mountain climbers who attempt to scale very tall peaks, such as Mount Everest (8850 m), may develop severe altitude sickness. They may suffer extreme headaches, be unable to breathe, and lose muscle co-ordination. The Respiratory System As you sit reading, you are carrying out a variety of body processes, but none more important than breathing in oxygen and exhaling carbon dioxide. This is the main purpose of the respiratory system. Without this exchange of gases, you would be unable to survive. The respiratory system shown in Figure 2.31 is made up of structures and organs that move oxygen into your body and carbon dioxide out of your body. Your lungs are important organs in this system because they deliver oxygen for cellular respiration and excrete carbon dioxide. Breathing is the process that brings oxygen into your body. Breathing begins when you inhale air through your nose or mouth. The air is warmed and filtered by tiny hairs, called cilia, and sticky mucus in your nose. The cilia and mucus trap dirt and other particles and either push these particles back out the nostril or down into the digestive system. The air continues down into the pharynx, past the epiglottis and through your larynx, or voice box. The larynx contains your vocal cords, which vibrate as air passes through them, producing the sounds of your voice. Then the air goes into the airway passage called the trachea. You can feel your trachea by gently rubbing your hand up and down on your neck. The bumps you feel are C-shaped bands of cartilage that maintain the tubular shape of the trachea and are similar to the ridges of a vacuum hose. nasal cavity pharynx epiglottis larynx esophagus trachea bronchus right lung bronchiole left lung Figure 2.31 The structures of the respiratory system 90 MHR Unit 1 Cells and Systems

31 At the base of the trachea branch two tubes called the bronchi (singular: bronchus). Air passes through both of these tubes and goes directly to your lungs. Air continues down the bronchi, which branch into smaller air tubes called bronchioles. Finally, the air reaches tiny, thin-walled sacs called alveoli (singular: alveolus). There are millions of alveoli at the ends of the bronchioles, and this is where gas exchange takes place. Gas Exchange in the Alveoli You can see in Figure 2.32 that each alveolus is surrounded by capillaries. Notice how each alveolus resembles a bunch of grapes on a stem. This is where the respiratory structures and circulatory structures interact. In Figure 2.33, you can see deoxygenated blood coming from the capillaries surrounding the alveolus. Carbon dioxide diffuses into the alveolus, and oxygen diffuses the other way into the capillaries and binds with the red blood cells. The oxygenated blood returns to the heart to be pumped to the rest of the body. This whole process is called gas exchange. alveoli air red blood cells bronchiole artery capillaries CO O 2 2 O 2 CO 2 O 2 alveolus CO 2 CO 2 O 2 CO 2 O 2 vein alveolar sac capillary Figure 2.32 Enlarged alveoli. Gas exchange occurs where the alveoli, capillaries, and blood vessels meet. Figure 2.33 Gases move back and forth between the alveolus and the surrounding blood vessels. Reading Check 1. Describe the path air must take to reach the lungs. 2. What is the difference between bronchi and bronchioles? 3. Name the gases exchanged between the alveoli and capillaries. 4. How does the structure of the alveoli speed up gas exchange? 5. What structures from the respiratory and circulatory systems are involved in gas exchange? Chapter 2 Human body systems work independently and together. MHR 91

32 internet connect Go to for more information on the effects of smoking. Smoking Many respiratory diseases such as lung cancer and emphysema result from smoking tobacco products, such as cigarettes or cigars. Emphysema causes the alveoli walls to lose their elasticity (see Figure 2.34). This makes breathing increasingly difficult as the disease progresses. Smoking is also linked to heart disease. Often people who have respiratory diseases caused by smoking will also have heart disease. What is in a cigarette? Smoking is the number one cause of lung cancer. There are over 4000 chemicals in a cigarette. Fifty of these chemicals are carcinogenic. This means research has shown that exposure to these chemicals can potentially cause cancer. The top six most harmful chemicals in cigarettes and tobacco products are nicotine, tar, carbon monoxide, formaldehyde, hydrogen cynanide, and benzene. Smoking also destroys the cilia lining your respiratory system so that dirt and other particles trapped in the mucus cannot be removed easily. Figure 2.34 A healthy lung (left) and a diseased lung showing the effects of smoking (right) 92 MHR Unit 1 Cells and Systems

33 Checking Concepts 1. Describe the pathway blood follows through the heart. 2. What is the difference between an artery and a vein? 3. Describe three components of blood. 4. What materials are found in plasma? 5. How are the functions of the atria and ventricles different? 6. Describe the two blood vessel networks in the circulatory system. 7. Describe the structure and function of the trachea. 8. What process occurs in the alveoli? 9. Describe two consequences of smoking. 10. Why can pneumonia lead to serious illness? 11. Fill in the blanks with the correct term. Blood is made up of: (a), which is a clear, yellowish. (b), which carry from the lungs to the body. (c), which fight bacteria and viruses. (d), which help prevent serious bleeding by helping blood. Understanding Key Ideas 12. How are the circulatory system and respiratory system interrelated? 13. What volume of blood does your body pump in a day or 24 hours? 14. If your body had a disease that reduced the number of your red blood cells, how would your body be affected? 15. Explain how the pulmonary artery and the pulmonary vein differ from all other blood vessels. 16. Explain the relationship for each set of terms below. (a) superior vena cava, inferior vena cava (b) heart, blood, blood vessels (c) red blood cells, hemoglobin (d) arterioles, capillaries, venules (e) carbon dioxide, oxygen, alveoli 17. At altitudes of 5500 m above sea level, the body has more difficulty functioning because the concentration of oxygen is lower. The highest city in the world is Wenzhuan, in the Himalayas, at an elevation of 5099 m above sea level. How does your knowledge of the circulatory and respiratory systems help you make a connection between these two facts? 18. The following diagram is another way to illustrate the circulatory system. Which terms below match the letter labels on the diagram? A B C D E F G H (a) (b) (c) (d) (e) (f) (g) (h) aorta capillary inferior vena cava kidney lungs pulmonary artery pulmonary vein superior vena cava Pause and Reflect Imagine there is a red blood cell in your body that has just been produced. Write a short story about the voyage of this red blood cell through the body. Chapter 2 Human body systems work independently and together. MHR 95