in the form of carbohydrates, fats, proteins, vitamins, and minerals

Transcription

1 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

2 Four Food Groups One way to make sure your diet is healthy is to eat a variety of foods from four food groups: grain products, vegetables and fruit, milk products, meat and alternatives (see Figure 2.6). Food Pyramid Another way to determine whether your diet is healthy is to compare it to a food pyramid (see Figure 2.7). Each coloured band represents one of six (instead of four) food groups: grains, vegetables, fruits, oils, milk products, and meat and beans. The width of each band tells you how much you should eat from that group. The wide part of the band means you should choose foods from that group that are low in solid fats and added sugars. The further up the pyramid you move, the more fats and sugars the foods contain. Whole wheat pasta with tomato sauce would be at the bottom of the grains band. Prepackaged macaroni and cheese would be much higher up. Figure 2.6 Choose foods from each of these four food groups. Figure 2.7 Choose foods in moderation (in appropriate amounts) from each of the coloured bands in this food pyramid. The person climbing the stairs on the pyramid means that an active lifestyle, along with the foods you eat, is important to your health. (Based on the USDA s MyPyramid.) grains vegetables fruits oils meat and beans milk products Food Availability Usually, our diets reflect what we can buy at our local grocery store or farmer s market, or what we may grow. Our diets may also reflect the traditional foods of our families. In some communities, traditional foods provide a valuable source of nutrients. Canadians living in the North may get their iron from the liver of a Canada goose or seal. Other Canadians, who live near oceans, may eat mussels, clams, and kelp, which are good sources of calcium. Although our food may come from different places, all Canadians need to make the right food choices to maintain healthy bodies. Chapter 2 Human body systems work independently and together. MHR 65

3 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

4 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

5 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

6 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

7 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.

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 2-5 Does Chemical Digestion Begin in the Mouth? SkillCheck Measuring Controlling variables Evaluating information Working co-operatively Safety Wear safety goggles. Wear protective clothing. Handle chemicals safely. Be careful and use appropriate equipment when handling hot objects. Be careful when handling electrical equipment. Wash your hands thoroughly after doing this investigation. Materials 4 test tubes test tube rack 100 ml graduated cylinder 10 ml graduated cylinder two 250 ml beakers tap water oatmeal (not instant) diastase solution (saliva substitute) sugar measuring spoon medicine dropper iodine solution Benedict s solution hot plate test tube clamp When food is ingested, mechanical digestion breaks down the food into small pieces called boli (singular: bolus). Enzymes also start to break down complex carbohydrates into simple carbohydrates. In this investigation, you will determine tests for simple and complex carbohydrates and use these tests to investigate the chemical digestion of oatmeal. Question What is the evidence that chemical digestion begins in the mouth? Procedure Part 1 Preparing Your Samples 1. Develop and complete a data table like the one below. Test Tube Contents Observations Number Put on your safety equipment before continuing. 3. Fill a beaker with 100 ml of water. Add a handful of oatmeal and allow it to stand for 10 min. Stir once or twice. 4. After 10 min, pour off the milky white liquid into another beaker. This will be your complex carbohydrate or starch mixture. 78 MHR Unit 1 Cells and Systems

16 Conduct an INVESTIGATION Inquiry Focus 5. Wash out the beaker you just emptied. Refill the beaker with water and place it on a hot plate. Heat the water until just below boiling. 6. Measure 10 ml of starch mixture into test tubes 1, 2, 3, and 4. Part 2 Testing for Iodine 7. Add four drops of iodine solution to test tube 1. Record your observations. Part 3 Testing for Sugar 8. Dissolve 5 g of sugar in 25 ml of water. Measure 10 ml of this sugar solution into test tube Add four drops of Benedict s solution to test tube 2 and heat it in the hot water in the beaker on the hot plate. Record your observations. Part 4 Investigating Chemical Digestion 10. Add 10 drops of the diastase solution to test tubes 3 and 4 and gently swirl. Wait 5 min. Diastase is an enzyme similar to the enzyme found in your saliva. 11. Add four drops of iodine solution to test tube 3. Record your observations in your table. 12. Add four drops of Benedict s solution to test tube 4. Place the test tube in the boiling water and leave it there for 5 min. Record your observations. 13. Allow solutions to cool and dispose of them carefully as instructed by your teacher. 14. Clean up and put away the equipment you have used. Analyze 1. Describe how you tested for the presence of starch. 2. Describe how you tested for the presence of sugar. 3. What effect did the diastase solution have on the starch solution? 4. What effect did the diastase solution have on the sugar solution? Conclude and Apply 1. How did your results provide evidence that chemical digestion begins in the mouth? Remember, diastase acts in the same way as an enzyme found in saliva. Science Skills Go to Science Skill 2 for information about controlling variables. Chapter 2 Human body systems work independently and together. MHR 79

17 Too Much Sugar Not So Sweet! Can your body get too much of a good thing? The millions of cells in your body need energy to work and that energy comes from the sugar glucose. So how can too much glucose in the body be bad? For glucose to enter cells, helpers called receptors are needed. These receptors act as doors to let glucose pass from the blood through the cell membrane. A chemical called insulin unlocks the doors to allow glucose to enter the cells. Special cells in the pancreas make insulin. If the pancreas cannot make insulin properly, glucose cannot enter the cells and stays in the blood. This is known as type 1 diabetes. If there are not enough receptors, glucose also remains outside the cells and stays in the blood. This condition is called type 2 diabetes. If glucose stays in the blood, a person feels tired because the cells are not getting the energy they need to function. The kidneys have to work harder to get rid of the excess glucose in the blood. This can result in high blood pressure and, eventually, kidney failure. Nerve cells do not get enough energy from glucose to pass information to the heart, so the heart does not pump efficiently. This could lead to a heart attack. Blood flow drops because nerve cells in the blood vessels are affected. This could lead to blindness, prevent sores from healing, and cause confusion or even a coma. Type 2 diabetes is the most common form of the disease, and millions of Canadians have it. The number continues to climb, with large increases reported in the number of young Canadians having the disease. Type 2 diabetes can affect anyone, but some groups are more likely to develop it. It is much more common in Aboriginal Canadians and Hispanic, Asian, South Asian, and African Canadians. At present, there is no cure for diabetes, but drugs, healthy eating, and regular exercise can control the disease. Maintaining a healthy weight is an important factor in controlling diabetes. In the future, scientists may find cures if they can transplant healthy pancreatic cells into type 1 diabetics and help cells produce more receptors for type 2 diabetics. Questions 1. What two requirements are necessary for glucose to enter cells? 2. How does type 1 diabetes differ from type 2 diabetes? 3. If you were a family doctor, what recommendations would you give people who are at risk for diabetes? 80 MHR Unit 1 Cells and Systems

18 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