Digestion Function PDF

SECTION The Function of Digestion 10.1 Key Terms Macromolecules and Living Systems Figure 10.1 shows the three main fluid compartments of the body: the cytoplasm inside macromolecule the...

SECTION The Function of Digestion 10.1 Key Terms Macromolecules and Living Systems Figure 10.1 shows the three main fluid compartments of the body: the cytoplasm inside macromolecule the cells, the fluid between the cells (the interstitial fluid), and the fluid in the blood. metabolism The fluid in these compartments is mostly water, which makes up more than 60 percent essential nutrient of the body. These compartments also contain and are composed of thousands of monosaccharide different kinds of molecules and ions. Some of these molecules and ions—such as disaccharide water, phosphates, hydrogen ions, and sodium ions—are small and simple. They are polysaccharide inorganic (non-living) matter. glycogen lipid volume of fluid inside cells volume of fluid outside cells (intracellular fluid) = 27 L-30 L (extracellular fluid) = 14 L-16.5 L amino acid peptide bond polypeptide cell capillary hydrolysis membrane wall enzyme volume of fluid volume of fluid in alimentary canal cytoplasm between all cells blood plasma of the body (liquid portion of mechanical digestion = 11 L-13 L blood) = 3.0 L-3.5 L chemical digestion Figure 10.1 Distribution of body fluids in the adult human. These fluids are mostly water, and they move freely in and out of the cell in both directions. Other molecules, called organic molecules, contain carbon bonded to hydrogen, macromolecule a very large molecule made as well as to other atoms, such as oxygen, sulfur, and nitrogen. Larger, more complex up of smaller molecules assemblies of organic molecules, called macromolecules, are also known as nutrients. that are linked together These nutrients are the raw materials that our bodies need to provide energy, to metabolism the regulate cellular activities, and to build and repair tissues. Regardless of their size or sum total of all of the complexity, all organisms require nutrients to perform their life functions and to obtain chemical reactions that occur in an organism energy for survival. Macromolecules are often grouped into four major categories: carbohydrates, lipids essential nutrient a nutrient that cannot (such as fats), proteins, and nucleic acids. Energy released from these macromolecules, be made by the body, and matter supplied by them, is used to maintain the body’s metabolism—all the and must therefore be chemical processes carried out by cells to maintain life. obtained from food Together, the four major categories of macromolecules are known as essential nutrients. Table 10.1 summarizes the four categories of macromolecules and their main functions in the body. Read on to learn more about macromolecules and how the human digestive system breaks down the macromolecules in the food we eat into forms that our bodies can use. Carbohydrates Carbohydrates are macromolecules that always contain carbon, hydrogen, and oxygen—and almost always in the same proportion: two atoms of hydrogen and one atom of oxygen for every atom of carbon. Carbohydrates provide short-term or long-term energy storage for organisms. There are two main types of carbohydrates: simple sugars and polysaccharides. 402 MHR Unit 4 Animals: Structure and Function Table 10.1 Four Major Categories of Macromolecules Macromolecule Main Functions Examples Carbohydrates provide materials to build cell membranes glucose, fructose, lactose, provide quick energy for use by cells maltose, starch, glycogen, cellulose Lipids store energy reserves for later use by cells fats, oils, waxes cushion and insulate internal organs provide materials to build cell membranes Proteins provide structure and support for blood cells, insulin, hemoglobin, body tissues, and muscles collagen, antibodies, aid in muscle movements, such as contraction enzymes act as catalysts to speed up chemical reactions in the cells provide immunity against infection and disease transport ions in cell membranes Nucleic acids contain the organism’s genetic information deoxyribonucleic acid (DNA), direct the organism’s growth ribonucleic acid (RNA) Monosaccharides Simple sugars, or monosaccharides (mono means one; sacchar means sugar), are monosaccharide a carbohydrate molecules with three to seven carbon atoms (and the corresponding simple sugar with three number of hydrogen and oxygen atoms). Examples of monosaccharides are glucose to seven carbon atoms (the sugar found in blood) and fructose (the sugar found in fruit). Disaccharides, disaccharide or double sugars, are made up of two simple sugars (di means two). Some common a sugar made up of disaccharides are sucrose (table sugar), maltose (the sugar found in germinating grain), two monosaccharide molecules and lactose (the sugar found in dairy products). polysaccharide Polysaccharides a large molecule made up of many linked Complex carbohydrates that consist of many linked simple sugars are called monosaccharide polysaccharides (poly means many). Examples are starch, cellulose, and glycogen, molecules a polysaccharide made up of glucose sub-units. Starch performs the important function glycogen a of storing energy in plants. Glycogen performs the same function in animals. polysaccharide made up of glucose units Lipids Lipids are a group of macromolecules that have one important property in common: lipid an organic they are insoluble in water. The basic structure of lipids is a molecule of glycerol compound that does (an alcohol) consisting of three carbon atoms, each attached to a fatty acid chain not dissolve in water, (an acid with a long tail of carbon and hydrogen atoms). Lipids store 2.25 times more such as fat and oil energy per gram than other biological molecules; therefore, some lipids function as amino acid a building energy-storage molecules. Other lipids, called phospholipids, form the membrane block of protein that separates a cell from its external environment. Examples of lipids are fats, such peptide bond a bond that holds together the as butter and lard, and oils, such as olive oil and safflower oil. amino acids in a protein polypeptide a linear Proteins chain of several amino Proteins are assembled from small sub-units that are known as amino acids. Most acids linked by peptide protein molecules are made up of hundreds of amino acids joined together by peptide bonds bonds into one or more chains. These chains are called polypeptides. Most enzymes are proteins, and so are antibodies, which combat disease. Proteins help build and repair muscles and cell membranes. Nucleic Acids Nucleic acids direct growth and development of all organisms using a chemical code. The two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Chapter 10 The Digestive System MHR 403  Breaking Down Macromolecules: Enzymes Before the body can use carbohydrates, lipids, and proteins, these large macromolecules hydrolysis a chemical reaction in which must be chemically broken down into molecules small enough to be absorbed by the cells water breaks apart lining the small intestine. The process that carries out this chemical breakdown is called macromolecules into hydrolysis (hydro is Greek for water, and lysis means to loosen). During hydrolysis, a smaller molecules water molecule is added to the macromolecule (the carbohydrate, protein, or lipid); enzyme a protein this breaks the chemical bonds that hold together the smaller molecules from which molecule that helps speed up important the macromolecule is made. This breakdown of the chemical bonds involves a special chemical reactions in class of protein molecules called enzymes, which are secreted by cells in the digestive the body tract. Enzymes act as catalysts, which are substances that increase the rate of chemical reactions without being used up in the reactions. There are three main types of digestive enzymes, each of which breaks down one type of macromolecule, as shown in Table 10.2. Table 10.2 Types of Digestive Enzymes Type of Enzyme Macromolecule It Breaks Down Product of Breakdown Example of Enzyme and Where It Functions Carbohydrase Carbohydrate Simple sugars Amylase: produced in the salivary glands and functions in the mouth Lipase Lipid Glycerol (an alcohol) Pancreatic lipase: produced in the pancreas and and fatty acids functions in the small intestine Protease Protein Amino acids Pepsin: produced by stomach glands and functions in the stomach Nuclease Nucleic acid Nucleotides Pancreatic nuclease: produced in the pancreas and functions in the small intestine Digestive enzymes help to speed up the process of hydrolysis, which is shown in Figure 10.2. You will learn more about enzymes and their roles in digestion later in this chapter. Figure 10.2 Large food Carbohydrate molecules are split into smaller molecules by hydrolysis. Specific enzymes speed up these reactions. polysaccharide + water Carbohydrase After hydrolysis, the smaller molecules can pass through disaccharide + water monosaccharide molecules cell membranes. Lipid Lipase glycerol fatty acid lipid + water molecules molecules Protein Protease protein + water amino acid molecules Nucleic Acid Nuclease nucleic acid + water nucleotides 404 MHR Unit 4 Animals: Structure and Function The Vital Roles of Minerals and Vitamins Other substances that are vital to life, in varying amounts, are minerals and vitamins. Minerals and vitamins are inorganic and organic substances that enable chemical reactions to occur and aid in tissue development, growth, and immunity. All of these substances are needed by a healthy, functional human body. Table 10.3 shows some minerals and vitamins, and their functions in the human body. Table 10.3 Functions and Possible Sources of Selected Vitamins and Minerals Key Functions in the Body Possible Sources Mineral magnesium: dark, Calcium forming bone leafy greens conducting nerve signals contracting muscle clotting blood Iron producing hemoglobin Magnesium supporting enzyme functions calcium: producing protein dairy products Potassium conducting nerve signals contracting muscle potassium: grains vitamin B1: beans Sodium conducting nerve signals balancing body fluid Vitamin vitamin D: fish A (Carotene) good vision healthy skin and bones iron: red meat B1 (Thiamine) metabolizing carbohydrates growth and muscle tone C (Ascorbic acid) healthy bones, teeth, gums, and blood vessels vitamins A, C, boosting immune system and E: fruit sodium: salt D absorbing calcium forming bone E strengthening red blood cell membranes The Many Roles of Water in the Body Water makes up about two thirds of the body’s mass and is needed for the proper functioning of all cells and organs. Its many roles include transporting dissolved nutrients into the cells that line the small intestine flushing toxins from cells lubricating tissues and joints forming essential body fluids, such as blood and mucus regulating body temperature (by sweating) eliminating waste materials (in urine and sweat) Water is vital for maintaining the body’s fluid balance, the condition in which the amount of fluid lost from the body equals the amount of fluid taken in. A constant supply of water is needed to replenish the fluids lost to normal, daily bodily functions. An average adult produces 1.5 litres (6.3 cups) of urine per day and loses about 1 litre of water through the breath, perspiration, urine, and bowel movements. Chapter 10 The Digestive System MHR 405  Activity 10.1 How Do You Take Your Macromolecules? There are two main reasons why food spoils: the growth Procedure of microorganisms (mostly bacteria and fungi) and the 1. Choose one example each of a food that is mostly breakdown of fats, which makes foods rancid. Bacteria carbohydrate, fat, or protein that you have on hand need water to grow in, and the earliest food preservation at home. technologies involved drying and smoking foods to remove the water and kill any potential bacteria or parasites. 2. Examine the items, their ingredient lists, and the A variety of techniques to preserve foods are used today. packaging for clues to how each has been preserved for Some are improvements on old technologies, some are best long-term storage. suited to particular types of foods, and a combination of techniques is often used. Most techniques simply prolong Questions the “shelf life” of the food. No technique is perfect, but some 1. Create a table and list each of the foods and the are better than others at preserving the nutrients in food. technologies used to preserve them. Salt, one of the earliest food preservatives, is still in use and 2. Choose one of the foods and use library resources or the is currently being targeted by physicians as a cause of high Internet to research the method behind the technology blood pressure. A more modern technology—the use of or combination of technologies used to preserve the trans fats—was thought to solve the problem of food going food, and why the technique works. rancid, but it is being re-evaluated amid charges that it causes heart disease. 3. Describe the advantages of this technology. Other techniques fall into broad categories of lowering 4. Describe the disadvantages of this technology. the pH, raising the temperature, lowering the temperature, using preservative spices or chemicals as additives, and 5. Identify any chemical preservatives in the foods you have sealing the food from air. One of the newer and more examined, and use the Internet to research the role of controversial techniques is known as irradiation and the preservatives and any possible side effects. involves treating the food with ionizing radiation. Materials reference books computer with Internet access Learning Check 1. What is the primary function of carbohydrates in 4. If an athlete runs for 15 minutes, which the human body? macromolecules are likely to break down first in 2. What is the difference between a monosaccharide the athlete’s body? and a disaccharide? Give an example of each. 5. Which macromolecules would provide the greatest 3. Explain how macromolecules are broken down for benefit as a long-term energy storage molecule to use in the body, as shown in Figure 10.2. a bird that migrates long distances? 6. Name three of the functions of proteins in the human body. 406 MHR Unit 4 Animals: Structure and Function How Animals Obtain Their Food As discussed in Chapter 1, some organisms, known as autotrophs, obtain energy by making their own food, usually using sunlight. Other organisms, known as heterotrophs, must consume other organisms to obtain energy-yielding food. Animals cannot produce their own food, so they use a wide variety of processes and behaviours to search for, obtain, and take in their food. Despite their many shapes, sizes, and food preferences, all animals obtain their food through one of four means, called feeding mechanisms. These feeding mechanisms include filter feeding, substrate feeding, fluid feeding, or (as humans do) bulk feeding. The four types of feeding mechanisms are shown in Table 10.4. By observing the mouth or other feeding device of an organism, it is usually possible to tell what type of feeder it is. Table 10.4 Animal Feeding Mechanisms Description Example Filter feeders are aquatic animals that use a body tube sponge structure similar to a filter basket to gather organisms, such as protists, bacteria, and the larvae of many aquatic animals, suspended in the surrounding water. The filter feeder siphons water into its mouth and then filters it to obtain small organisms to digest. The tube sponge is a filter feeder. Other examples include flamingoes, tube worms, clams, barnacles, and baleen whales. Substrate feeders live in or on their food source and caterpillar eat their way through it. Examples of substrate feeders include caterpillars and earthworms. Caterpillars eat their way through the green tissues of leaves. Earthworms eat their way through the soil, ingesting soil particles containing partially decayed organic material as they go. Fluid feeders obtain food by sucking or licking butterfly nutrient-rich fluids from live plants or animals. Fluid feeders have mouth parts that are adapted to pierce or rip skin or leaf tissue. The same or other mouth parts are used to suck or lick the blood or sap that is their food. Examples of fluid feeders include mosquitoes, ticks, aphids, spiders, bees, butterflies, vampire bats, and hummingbirds. Bulk feeders include many animals and most vertebrates (including humans). Bulk feeders ingest fairly large pieces of food and some, like the great blue heron, swallow their food whole. Other bulk feeders use tentacles, pincers, claws, fangs, or jaws and teeth to kill prey, to tear off pieces of meat or vegetation, or to take in mouthfuls of animal or plant food. great blue heron Chapter 10 The Digestive System MHR 407  The Four Stages of Food Processing After an animal has obtained its food, the nutrients in the food must get into the individual cells of the animal’s body in a usable form. The essential function of an animal’s digestive system is to break food down into small, soluble units that can pass through cell membranes. The digestive system breaks down food into useful substances that can be absorbed into the circulatory system. The circulatory system (to be discussed in detail in Chapter 12) transports these substances to the individual cells of the body. Whatever an animal’s source of food, type of food, or feeding method, digestion alimentary canal the tube through which of food occurs in four stages: food is processed, 1. ingestion—the taking in or eating of food beginning at the mouth and ending at the anus; 2. digestion—the breakdown of food by mechanical and chemical processes into also known as the molecules small enough for cells of the body to absorb digestive tract 3. absorption—the transport of the products of digestion from the digestive system mechanical digestion into the circulatory system, which distributes them to the rest of the body the physical breakdown of large pieces of food 4. elimination—the removal of undigested solid waste matter from the body into smaller pieces in the mouth by the action Digestion and the Alimentary Canal of teeth, beak, or other To digest their food, most animals have a digestive tract that consists of a long open similar structures, and by contractions and tube. This tube, called the alimentary canal, has a mouth at one end to ingest food churning motions in the and an anus at the other end to eliminate waste. As food moves along this tube, stomach different organs of the digestive system process the food in different ways—rather like chemical digestion a production line in a factory. the chemical breakdown of nutrient molecules One example of an open tube structure is the alimentary canal of the earthworm. into smaller molecules In the earthworm, shown in Figure 10.3, food enters the mouth and passes into the by enzyme action pharynx, or throat. The esophagus then channels the food into the crop, a pouch-like organ in which food is softened and stored. The muscular gizzard churns and grinds the food, and the food is further digested in the intestine. crop intestine pharynx gizzard mouth anus esophagus Figure 10.3 The earthworm has a simple digestive tract. Decaying plant and animal matter in the soil provides the earthworm with nutrients. Undigested materials pass through the tract and are eliminated through the anus as worm castings. In more complex animals, food enters the mouth and is physically broken apart into smaller pieces by the teeth. The food is further broken apart as it moves along the digestive tract by the muscular contractions of the tube itself. This process of physical breakdown of the food into smaller bits is called mechanical digestion. At the same time, various fluid-releasing glands in the mouth and further along the digestive tract add liquid and enzymes that help to break down the macromolecules of food into smaller molecules. This breakdown of macromolecules by enzymes is the process known as chemical digestion. Figure 10.4 shows a simple overview of the digestive process in a typical mammal. 408 MHR Unit 4 Animals: Structure and Function  Nutrient molecules absorbed by cells Undigested Breakdown into solid waster smaller molecules Figure 10.4 The four main stages Pieces Chemical of food processing in animals are: of food digestion (1) ingestion, the intake of food; (2) digestion, the breakdown of food into small molecules; (3) absorption, the Mechanical digestion transport of nutrient molecules across cell membranes; and (4) elimination, the expulsion of undigested waste. The Length of the Digestive Tract Although the function of the digestive system is the same in all animals, the length of the digestive tract varies according to the feeding habits of the species. Herbivores and omnivores (including humans) usually have longer digestive tracts, relative to their body size, than carnivores. For example, compare the digestive tracts of a rabbit (a herbivore) and a fox (a carnivore) in Figure 10.5. Because the cellulose walls in plant tissues are more difficult to digest than animal tissues, most herbivores have relatively longer digestive tracts, which allows the extra time needed for digestion. In Section 10.2, you will focus on the structure and function of the human digestive tract. Herbivore Carnivore fox rabbit esophagus stomach Herbivores have longer small intestines. Carnivores have shorter small intestines. cecum large intestine anus Figure 10.5 The digestive tract of a small herbivore, such as a rabbit, is longer than that of a small carnivore, such as a fox. In both digestive tracts you can see the cecum, a pouch at the beginning of the large intestine that receives waste material from the small intestine. Infer What might account for the relative difference in the size of the cecum between these two animals? Chapter 10 The Digestive System MHR 409  Section 10.1 RE V IE W Section Summary There are four major categories of macromolecules that Water helps transport materials around the body, contain the essential nutrients needed to maintain life: lubricate joints, form vital fluids such as blood, and carbohydrates, lipids, proteins, and nucleic acids. regulate body temperature. Macromolecules are chemically broken down by To digest their food, most animals have a digestive tract hydrolysis, a process that uses certain enzymes that consists of a tube known as the alimentary canal. as catalysts. The four stages of food processing in animals are ingestion, digestion (mechanical and chemical), absorption, and elimination. Review Questions 1. K/U What are the four major macromolecules that 11. A Use the information in Table 10.3 to answer the are needed by the body, and why are they important? following questions. 2. K/U Summarize the functions of lipids in the body. a. Which vitamin is involved in the absorption of calcium from foods? 3. C Use Tables 10.1 and 10.2 to create a graphic organizer, such as a spider map, to show the four major b. Identify a vitamin that would be useful to take for macromolecules. For each grouping, include a list of night blindness. the characteristics that define the grouping, including c. What vitamin deficiency could lead to bone structure, function, examples, and the digestive malformations? enzymes that make them usable by the body. 12. T/I To prevent cramping during a soccer match, 4. C Use what you have learned so far in this chapter an athlete is advised to eat a banana and drink a glass to make a Venn diagram that compares and contrasts of milk before the game. Explain why these foods monosaccharides, disaccharides, and polysaccharides. might be helpful in preventing cramps. 5. C Create an analogy to explain to another student 13. A Classify the following organisms as filter feeders, why a polysaccharide is considered a long-term source fluid feeders, substrate feeders, or bulk feeders. of energy, while a monosaccharide is considered a a. An animal that feeds on plant sap has a long, short-term source of energy. beak-like mouthpart that can pierce plant tissues. 6. T/I A dessert topping for ice cream contains b. An animal eats its way through the upper surface of maltose, soybean oil, and salt. Identify the kinds of a leaf. macromolecules and minerals that are in this topping. c. An animal captures its prey with its teeth and tears off pieces of meat. 7. T/I Why must macromolecules be broken down d. An aquatic animal has gills in which mucus traps into smaller molecules during digestion? food. 8. K/U In your own words, describe the structure of 14. T/I A biologist studying the alimentary canal in a protein. animals notices that herbivores such as deer have an 9. T/I Explain why humans cannot survive for more enlarged cecum, whereas carnivores like foxes have a than a few days without drinking water. small cecum or none at all. The researcher also finds 10. C Copy the table below into your notebook and that the cecum hosts a high concentration of bacteria. complete it. Refer to Figure 10.4 to help you. Give your How might the concentration of bacteria be related to table a title. the size of the cecum in herbivores? Part of digestive 15. C Use a graphic organizer, such as a flowchart, tract where Process Definition process occurs to show clearly how the words digestion, elimination, absorption, and ingestion are related. Chemical digestion 16. A Using your knowledge of evolution from Unit 3, Mechanical explain why so there is so much diversity in feeding digestion mechanisms in animals. 410 MHR Unit 4 Animals: Structure and Function  SECTION The Human Digestive System 10.2 The human digestive system, like other body systems, is made up of a group of organs Key Terms working together. The digestive tract and the organs associated with it are shown salivary glands in Figure 10.6. In this section, you will learn about the structure and function of the saliva digestive system, and how each part of this system plays a role in transforming food into the energy and materials the body needs to survive. esophagus peristalsis Accessory Organs The Digestive Tract gastric juice (structures that (organs that chyme aid digestion) contain food) pepsin salivary glands duodenum mouth villi liver jejunum esophagus ileum bile gall bladder stomach pancreas small intestine large intestine rectum anus parotid gland accessory parotid gland parotid duct sublingual gland submandibular gland Figure 10.6 The digestive tract and associated organs Figure 10.7 Each parotid gland and submandibular take up a significant portion of the space in a human body. gland release saliva into the mouth through the parotid The small intestine is over 6 m long and 2.5 cm in diameter. duct and the submandibular duct. The sublingual glands The large intestine is about 1.5 m long and 5 cm in diameter. release saliva into the mouth through many smaller ducts. Parts of the Human Digestive System The specialized organs in the human digestive tract start with the first point of salivary glands glands contact—the mouth. Even before you take your first bite of food, the smell or sight of in the mouth that food can trigger the salivary glands, shown in Figure 10.7, to secrete a watery fluid produce saliva to begin called saliva into the mouth. There are three pairs of salivary glands in the mouth. the chemical digestion Chemical digestion begins with saliva. Saliva contains an enzyme called amylase of food that starts to break down the starches in food into simpler sugars. Saliva dissolves saliva a watery secretion in the mouth water-soluble food particles. It stimulates the taste buds, making it possible to taste the that begins the digestive flavours of the food. It also lubricates the food to make it easier to swallow. Mechanical process digestion also begins in the mouth as your teeth bite, tear, and grind food into smaller pieces. This mechanical action also exposes more of the surface area of the food to the saliva, making it more accessible for chemical digestion. Chapter 10 The Digestive System MHR 411  The Esophagus As you chew your food, your tongue helps mould and smooth it into a soft mass, called esophagus the muscular tube through a bolus, that the tongue then pushes to the back of your mouth. When you swallow, the which food passes bolus enters the top of the esophagus to begin its passage to your stomach. The opening from the mouth to the of the esophagus lies next to the opening of your windpipe, or trachea, which carries stomach air to and from your lungs. To prevent food from going down the wrong tube and peristalsis a wave-like choking you when you swallow, the opening of the trachea is closed by a valve called series of muscular contractions in the the epiglottis when you swallow. esophagus The esophagus is a hollow muscular tube that transports each bolus of food to the stomach in a series of wave-like muscular contractions called peristalsis, shown in Figure 10.8. Glands in the lining of the esophagus produce mucus, which keeps the passage moist and aids in swallowing. The entrance to the stomach is controlled by a ring of muscle called the esophageal sphincter. This sphincter is normally closed to prevent the acidic contents of the stomach from backing up into the esophagus, but it relaxes to allow each bolus of food to enter the stomach. A C to stomach longitudinal muscle circular muscle Contraction of longitudinal muscles ahead of food mass contraction raa B D Contraction of circular muscles Contraction in circular muscle behind food mass layer forces food mass forward Figure 10.8 Peristalsis moves food through the esophagus by means of muscular contractions. When you vomit, or “throw up” your stomach contents, the contractions of the esophagus are reversed. Similarly, small amounts of acidic liquid can escape from the stomach and move up the esophagus into your throat. This is experienced as a burning sensation in the throat or chest, commonly called heartburn or acid reflux. Activity 10.2 Modelling Peristalsis In this activity, you will design and construct a working model 3. As a group, discuss the possible ways you might use the to demonstrate how the esophagus uses muscular action materials to construct your model. to move food along from the throat to the stomach. Could 4. Construct your model and use it to demonstrate the someone swallow a mouthful of juice while upside down? process of peristalsis. Safety Precautions 5. When you are finished your demonstration, clean the materials and leave them out to dry. Inform your teacher if you have any allergies to soaps or Questions detergents. 1. How are the textile fibres in the stocking analogous to the muscle fibres in the esophagus? Hint: Refer to Materials Figure 10.8 to help you with your answer. knee-high nylon stocking liquid soap or detergent tennis ball hand lens 2. What was the function of the water and soap in this water scissors model? What two secretions serve the same function in the esophagus? Procedure 3. As an optional extension to this activity, create a flipbook 1. Examine the materials provided by your teacher. to illustrate peristalsis so that a younger student could 2. Review the section on the esophagus, and refer to understand this process. Figure 10.8 to help you with this activity. 412 MHR Unit 4 Animals: Structure and Function The Stomach The stomach is a muscular, J-shaped organ in which food is temporarily stored while gastric juice a mixture further chemical and mechanical digestion takes place. This organ lies on the left side of hydrochloric acid, of the abdominal cavity, just below the diaphragm [DIH-uh-fram], which is the sheet salts, enzymes, water, of muscle that separates the heart, lungs, and ribs from the abdominal cavity. The walls and mucus that is of the stomach are folded like an accordion, allowing the stomach to expand after a produced by glands in the stomach to help meal, as shown in Figure 10.9. The stomach is lined with millions of gastric glands that digest food secrete gastric juice when stimulated by the presence of food. Gastric juice is made up of hydrochloric acid, salts, enzymes, water, and mucus. The mucus coats the walls of the stomach, protecting it from attack by the strongly acidic gastric juice. The rest of the gastric juice continues the chemical digestion of the food. food stored in this area esophageal sphincter three muscle layers (churn and mix food) pyloric sphincter (controls flow of chyme into the small intestine) food mixed and beginning part of churned in this area small intestine folds inside stomach (enable stomach to stretch and contract) Figure 10.9 Folds in the stomach wall allow it to expand and contract as it fills with food and then empties its contents into the small intestine. The stomach has three layers of muscle fibres that contract and then relax to churn chyme a thick liquid and mechanically break up pieces of food and mix them with the gastric juice. The produced in the result of this churning and mixing is a thick liquid called chyme [kihm]. At the lower stomach and made of end of the stomach is a muscular valve called the pyloric sphincter. When closed, this digested food combined with gastric juice valve keeps food in the stomach. The stomach usually does not digest the proteins that make up its own cells, pepsin an enzyme in gastric juice that helps because it has three methods of protection. First, the stomach secretes little gastric juice break down proteins until food is present. Second, some stomach cells secrete mucus, which prevents gastric into polypeptides juice from harming the cells of the stomach lining. Third, the stomach produces its protein-digesting enzyme, pepsin, in a form that remains inactive until hydrochloric acid is present. Once active, pepsin hydrolyzes proteins to yield polypeptides—a first step in protein digestion in the digestive tract. The stomach is surrounded by a network of nerves that help regulate the activities of SuggestedInvestigation the digestive system. These nerves initiate the stomach contractions that release partially ThoughtLab Investigation digested food into the small intestine. When the small intestine is full and still digesting 10-A, An Accident and an food, the stomach temporarily stores the chyme. When processed food has moved out of Opportunity the small intestine into the large intestine, the pyloric sphincter opens and the stomach pushes chyme into the first part of the small intestine—the duodenum. Chapter 10 The Digestive System MHR 413  Learning Check 7. Describe where the digestion of carbohydrates 10. If a person has the mumps, their submandibular begins in the body, the major glands involved, and glands are swollen. Analyze Figure 10.7, and decide the digestive secretions produced. which part of the body a doctor would examine to 8. Using Figure 10.8, explain how peristalsis works in help diagnose the mumps. the esophagus and its function in digestion. 11. A doctor orders a pH test of the esophagus for a 9. Analyze whether the epiglottis is closed and patient who is complaining about having heartburn covering the trachea or open in the following and a burning sensation in the chest. What do you situations, and explain why: expect the doctor to find and why? Use Figure 10.9 a. when the person is talking to identify the source of this problem. b. when the person is swallowing 12. Using your knowledge of basic chemistry from c. when the person is coughing previous studies, how do over-the-counter antacids, d. when the person is chewing such as calcium carbonate, help an individual with a gastroesophageal discomfort, such as stomach pain? The Small Intestine The small intestine is the part of the alimentary canal in which digestion is completed— duodenum a short, wide U-shaped section that is, the nutrient macromolecules are finally broken down into their component of the small intestine molecules. The nutrients are then absorbed through the membranes of the cells that into which food passes line the small intestine, and they pass from the digestive system into the circulatory from the stomach system. The circulatory system carries the nutrients to cells and tissues throughout the villi finger-like rest of the body. projections lining the surface of the small intestine that increase The Duodenum the surface area to The small intestine looks like a long, folded tube divided into three main regions. The improve the absorption first region after the stomach is the U-shaped duodenum. To speed up the process of of nutrients absorption, the walls of the small intestine are lined by folds that greatly increase the surface area through which nutrients can be absorbed. The folds are covered by tiny, finger-like projections called villi (singular villus). Each villus, in turn, is covered with many fine brush-like microvilli, as shown in Figure 10.10. As food passes through the duodenum, it receives secretions from two organs that support the function of the digestive system: the pancreas and the gall bladder. Figure 10.10 The lining of small intestine villi the duodenum is arranged duodenum in circular folds. Each fold is covered in tiny villi and microvilli, through which the absorption of nutrients into the bloodstream takes place. microvilli capillary villus network nucleus vein (carries artery (carries nutrient-laden oxygen-rich blood to the body, blood to the villi) via the liver) cell membrane 414 MHR Unit 4 Animals: Structure and Function The Jejunum and Ileum Following the duodenum is a structure called the jejunum, which is about 2.5 m long jejunum the portion of and contains more folds than the duodenum. The jejunum breaks down the remaining the small intestine that proteins and carbohydrates so the end products can be absorbed into the bloodstream. follows immediately The ileum, which is about 3 m long, contains fewer and smaller villi than either the after the duodenum duodenum or the jejunum. Its function is also to absorb nutrients, as well as to push ileum the portion of the remaining undigested material into the large intestine. the small intestine that follows immediately after the jejunum The Accessory Organs bile a greenish-yellow The pancreas and gall bladder are not part of the alimentary canal itself, but they fluid secreted by the are connected to the canal by ducts, as shown in Figure 10.11. Because of this close liver that helps digest fat association with the alimentary canal, the pancreas and gall bladder are referred to as accessory organs. (An accessory is something that aids or provides support to something else.) Fluids produced by the accessory organs are essential to the process of digestion. esophagus liver gall bladder stomach duodenum small intestine pancreas Figure 10.11 The pancreas and gall bladder secrete enzymes necessary for digestion. In an adult human, the pancreas secretes about 1 L of pancreatic fluid into the duodenum each day. Pancreatic fluid contains numerous enzymes that chemically digest carbohydrates, lipids, and proteins. The fluid also contains bicarbonate, which is very important to the function of the enzymes. The bicarbonate alters the pH of chyme from strongly acidic (pH 1) to weakly basic (pH 8), thereby producing conditions in which the enzymes in the pancreatic fluid can work most efficiently. The liver is the largest internal organ of the human body. In an adult, it is the size of a football, with a mass of about 1.5 kg. The main digestion-related secretion of the liver is bile, a greenish-yellow fluid mixture that is made up of bile pigments and bile salts. Bile pigments do not take part in digestion. They are waste products from the liver’s destruction of old red blood cells, and they are eventually eliminated with the feces. After bile is produced in the liver, it is sent to the gall bladder, which stores the bile between meals. Bile contains bile salts that are essential for the digestion of fats. Because fats are insoluble (that is, they cannot be dissolved) in water, they are suspended in the chyme as small droplets—like the blobs of fats that float up if you put a greasy dish in a sink of hot water. Bile salts act like detergent, physically breaking up the fat droplets into smaller fat droplets, and suspending the smaller fat droplets so they can disperse throughout the chyme. The many smaller fat droplets create a greater surface area to be exposed for digestive enzymes to chemically break down the fats in the small intestine: this makes it easier for the intestinal cells to absorb the fats. Chapter 10 The Digestive System MHR 415  Chemical Digestion and Absorption The bile and pancreatic fluid in the duodenum help break down carbohydrates, proteins, and lipids into smaller molecules that can be absorbed into cells that line the small intestine. Enzymatic digestion of macromolecules is performed by carbohydrases (which digest carbohydrates), lipases (which digest fats), proteases (which digest larger polypeptides), and nucleases (which digest nucleic acids). Figure 10.12 provides an overview of the sites of digestion of the four categories of macromolecules and how enzymes break them down step by step. Complex Carbohydrates Proteins Fats Nucleic Acids polysaccharides salivary amylase disaccharides Mouth proteins pepsin small polypeptides Stomach polysaccharides and smaller peptides fat droplets DNA and RNA disaccharides proteases (trypsin bile nucleases and chymotrypsin) carbohydrases (pancreatic amylase, fat droplets peptides nucleotides sucrase, maltase, (emulsified) and lactase) nucleosidases peptidases lipases Small nitrogen-containing glycerol and intestine monosaccharides amino acids bases, sugars, fatty acids and phosphates Figure 10.12 An overview of chemical digestion and absorption in the small intestine. Table 10.5 outlines some of the digestive enzymes and their digestive activities. You may find it helpful to refer to Table 10.5 as you read about the digestion and absorption of carbohydrates, proteins, lipids, and nucleic acids on the next few pages. Table 10.5 Selected Enzymes of the Digestive System Where Enzyme Nutrient Molecule Enzyme Origin of Enzyme Acts/pH Digested Products of Digestion Salivary amylase Salivary glands Mouth/7 Starch, glycogen Maltose (disaccharide) Pancreatic amylase Pancreas Small intestine/8 Starch, glycogen Maltose Carbohydrases Small intestine Small intestine/8 sucrase Sucrose Glucose + fructose maltase Maltose Glucose lactase Lactose Glucose + galactose Pancreatic lipase Pancreas Small intestine/8 Lipids Fatty acids and glycerol Proteases pepsin Stomach Stomach/1–2 Protein Peptides trypsin Pancreas Small intestine/8 Small polypeptides Smaller peptides chymotrypsin Pancreas Small intestine/8 Small polypeptides Smaller peptides Peptidases Pancreas and small intestine Small intestine/8 Peptides Smaller peptides and amino acids 416 MHR Unit 4 Animals: Structure and Function Factors That Affect Enzyme Action Two factors, temperature and pH, can affect the rate at which an enzyme functions Enzyme Reaction A to break down complex molecules. More energy is added at higher temperatures, so by Temperature the enzyme activity increases. The chemical bonds become too weak to maintain the (product per unit of time) enzyme’s shape. The enzyme becomes denatured, meaning that its molecular shape Rate of Reaction and structure (and, thus, its properties) are changed. (Think of the changes that occur to egg white—a protein—when it is heated.) For most human enzymes, the optimal temperature range is fairly narrow, peaking at about 37°C, as shown in Figure 10.13 (A). Enzymes also function best within an optimal pH range. Some human enzymes such as pepsin, shown in Figure 10.13 (B), function best at a low pH. Pepsin is found in the acidic environment inside the stomach. However, most human enzymes, such as 0 10 20 30 40 50 60 Temperature (°C) trypsin, function best in pH environments of about pH 6 to 8. Trypsin is found in the more neutral environment of the small intestine. Enzyme B Reaction by pH Absorption in the Small Intestine (product per unit of time) Monosaccharides are absorbed into the bloodstream through the lining of the Rate of Reaction small intestine as shown in Figure 10.12. They are transported to the liver, where monosaccharides (other than glucose) are converted into glucose. Glucose is carried from the liver to all parts of the body by the circulatory system, and is used pepsin trypsin by cells as a source of energy. The liver converts excess glucose into glycogen, which can be temporarily stored in the liver and, in much smaller amounts, in muscles. When the body needs additional energy, some of the stored glycogen is converted 0 2 4 6 8 10 pH back to glucose. Like monosaccharides, amino acids are carried by the bloodstream from the Figure 10.13 The proper small intestine directly to the liver. In the liver, amino acids are processed by various functioning of an enzyme is reactions and are either converted into sugars or used in energy-releasing chemical affected by (A) temperature reactions. Some of the amino acids resulting from these reactions undergo a series of and (B) pH. Most enzymes in humans, such as trypsin, which further transformations in the liver, and become a part of a nitrogen-rich waste called helps break down protein in urea. Urea is filtered by the excretory system and expelled from the body in urine. the small intestine, work best Other amino acids are carried by the circulatory system to the cells of the body, where at a temperature of about 40°C they are used to make enzymes and other proteins such as keratin, which forms skin and within a pH range of 6 to 8. and hair. Glycerol and fatty acid molecules are absorbed into the cells of the small intestine, where they are reassembled to form triglycerides. The triglycerides are coated with proteins to make them water-soluble. Protein-coated triglycerides pass SuggestedInvestigation from the cells of the small intestine into a network of vessels that transfer them into Inquiry Investigation 10-B, the bloodstream. In the blood, the protein coating is removed and the triglycerides Optimum pH for Two are broken down by lipase enzymes back to glycerol and fatty acids. These smaller Protease Enzymes molecules provide energy to the cells. Learning Check 13. Explain two functions of pancreatic fluid. 17. A family member has recently had a cholecystectomy, 14. What happens to fats before they are digested and a surgical procedure to remove his gall bladder. Now absorbed by the intestinal cells? Explain why this he must take medication to prevent diarrhea. Why occurs. would the removal of the gall bladder cause diarrhea? 15. Make a graphic organizer to show what happens to 18. A baby is born with a mutation that results in an partially digested food after it leaves the stomach, up unusually smooth small intestine that has far fewer to the stage where it leaves the small intestine. villi than a normal small intestine. Describe one possible consequence of this mutation. 16. What is the role of the gall bladder in digestion? Chapter 10 The Digestive System MHR 417  The Large Intestine After the nutrients in digested food have been absorbed from the small intestine into the bloodstream, the remaining material moves into the large intestine, or colon, shown in Figure 10.14. This part of the digestive system is much shorter and wider than the small intestine. The main function of the large intestine is to absorb water from the alimentary canal. About 90 percent of the water is absorbed back into the blood and extra-cellular fluids. The volume of the indigestible food matter (mostly indigestible plant matter) is therefore reduced by about two thirds. Figure 10.14 This view of a healthy colon shows its high number of blood vessels and its ring-like muscular wall. This image is of the final part of the large intestine, where it joins to the rectum. Billions of anaerobic bacteria (bacteria that do not live or grow in the presence of oxygen) in the colon break down undigested matter further. Some of these bacteria produce important vitamins, including folic acid, several B vitamins, and vitamin K, which are absorbed into the bloodstream through the colon. The leftover matter forms feces, which are pushed by muscular contractions of the colon into the rectum. The typical brown colour of feces is due to the bacterial breakdown of bilirubin. Bilirubin is a by-product of the breakdown of hemoglobin (the protein that carries oxygen in the blood). Bilirubin gets secreted into the bile in the liver. Fecal odour comes from gases produced by bacterial activity. The rectum stores the feces until they are eliminated at the anus. Table 10.6 summarizes the primary function of each structure in the digestive system and how long food usually remains in each structure as it is being digested. Table 10.6 Time Required for Human Digestion Digestive Primary Time Food Spends in Structure Function Each Structure Mouth Mechanical and chemical digestion 5–30 s Esophagus Transport (swallowing) 10 s Stomach Mechanical and chemical digestion 2–24 h Small intestine Mechanical and chemical digestion 3–4 h Large intestine Water absorption 18 h–2 days 418 MHR Unit 4 Animals: Structure and Function  Section 10.2 RE V IE W Section Summary The human digestive system is made up of the alimentary The large intestine absorbs water from the alimentary canal and three accessory organs: the liver, the pancreas, canal and forms feces, which are eliminated as solid and the gall bladder. waste. Food is transported from the esophagus to the stomach Different types of enzymes are involved in the chemical by wave-like muscular contractions known as peristalsis. digestion of carbohydrates, proteins, and fats. Although chemical digestion begins in the mouth and The levels of pH differ throughout the digestive system, continues in the stomach, most chemical digestion occurs to allow optimum enzyme function. in the small intestine. Review Questions 1. K/U Use the diagram below to answer the following 5. T/I Infer how the food reaches an astronaut’s questions. stomach when he or she is floating in zero gravity. a. Identify the body part(s) where digestion of 6. K/U Why does the acid in gastric juice not damage carbohydrates occurs. the wall of the stomach? b. Identify where digestion of proteins occurs. 7. K/U Which structural features of the small intestine c. Which is the longest section of the alimentary canal? increase surface area? Why is this important? d. Where does most absorption in the digestive system T/I Why are most digestive enzymes not found in 8. take place? the stomach? 9. A In what ways would a digestive system that did not use mechanical digestion differ from one A that does? 10. A After playing in the dirt, a child sticks her F fingers in her mouth and ingests a significant number of bacteria but does not get sick. Explain how this child’s digestive system protected her from these B G potentially toxic bacteria. H 11. K/U What would an individual need to do to replace C the function of their pancreas if their pancreas was removed? D I 12. T/I A new species of animal is found to have a E digestive system that uses very little mechanical digestion. Describe its digestive tract. 13. T/I A nutritionist recommends drinking water 2. C Create a graphic organizer, such as a flowchart before or after a meal, but not during a meal. Why or a table, that compares the chemical digestion of the might this be good advice? four types of macromolecules as they move through 14. C Use a graphic organizer to illustrate the the following body parts: oral cavity, esophagus, small interaction between the digestive system and the intestine, and large intestine. Include any enzymatic circulatory system. digestion that occurs along the way. 15. K/U Explain how your body absorbs water. 3. K/U The small intestine is divided into three different regions. Describe the structure and function of each of 16. C Use a graphic organizer, such as a main idea web these regions. or a fishbone organizer, to summarize the structure K/U Your friend is convinced that digestion begins in and functions of the large intestine in humans. 4. the stomach. Is this true or false? Explain your answer. Chapter 10 The Digestive System MHR 419  SECTION Digestive System Disorders 10.3 Key Terms Digestive system disorders can occur when any part of the system is not working properly during the digestive process. In this section you will learn about these peptic ulcer disorders, and how technological advances help doctors diagnose and treat them. inflammatory bowel disease Peptic Ulcers Crohn’s disease Abdominal pain, bloating, nausea, and loss of appetite can all be symptoms of a ulcerative colitis peptic ulcer. A peptic ulcer is a sore in the lining of the stomach or duodenum, hepatitis where hydrochloric acid and pepsin are present. Ulcers form when the tissues become cirrhosis inflamed because the protective mucus that covers the lining has weakened, as shown diabetes in Figure 10.15. Ulcers are very painful because exposed, unprotected tissue comes into contact with acidic gastric juice. They can occur in people of all ages. Most ulcers begin when populations of an acid-resistant bacterium, Helicobacter pylori, attach themselves to the wall of the digestive tract and prevent that area from producing the protective mucus. Because ulcers are caused by a bacterium, they can be treated with antibiotics that kill the bacteria. Along with antibiotics, doctors also often prescribe medications that reduce acidity in the stomach. Treatment may also include lifestyle changes, such as losing weight if overweight, avoiding alcohol, and not smoking. peptic ulcer a sore in the lining of the stomach or duodenum, endoscope most commonly caused by infection with the from power source bacterium Helicobacter pylori inflammatory bowel disease the general to video name for a group of monitor diseases that cause inflammation in the intestines Crohn’s disease Figure 10.15 This photo of a bleeding ulcer in the stomach was taken with an endoscope, a a form of inflammatory tube-shaped instrument with a tiny lens and light source that is inserted into the digestive tract. disease that can affect any part of the Inflammatory Bowel Disease alimentary canal from Often referred to as IBD, inflammatory bowel disease is a general name for a group the mouth to the anus of diseases that cause inflammation in the intestines. The incidence of inflammatory ulcerative colitis a form of inflammatory bowel disease is increasing in Canada—over 200 000 people (1 in 160) are living with disease that attacks the disease. IBD is a chronic disease, meaning that it is long lasting or recurrent. IBD the colon can only be treated—not cured—by a special diet and by taking medication to reduce pain and inflammation. The main forms of IBD are Crohn’s disease and ulcerative colitis. Crohn’s disease is a form of IBD that can affect any part of the alimentary canal from the mouth to the anus. Children with Crohn’s disease generally do not grow properly during puberty. They develop thinner bones that increase the future risk of fractures, and they experience poor muscle development. Ulcerative colitis is a form that attacks the colon. Symptoms of colitis include loose and bloody stools, cramps, and abdominal pain. In severe cases of IBD, it may be necessary for surgeons to remove the affected part of the colon and create a new external opening for digestive waste. Research scientists are trying to find out why these diseases of the digestive tract have been increasing among children, and why rates are much higher in western nations than in other countries. 420 MHR Unit 4 Animals: Structure and Function Constipation Constipation is a common disorder of the digestive system in which bowel movements are reduced to three per week or less and stools are dry, small, and difficult to eliminate. Constipation can be caused by inadequate water intake (which leaves the stools dry) and lack of good nerve and muscle function in the bowel. An unhealthy diet and lack of physical activity can also cause constipation. Although fibre is not a nutrient and is not digested, it is essential for maintaining a healthy digestive system. Fibre refers to parts of fruits, vegetables, and grains that are not broken down in the digestive system—they pass through the body almost unchanged. Foods rich in fibre include whole grain bread, brown rice, whole grain pasta, oats, beans, peas, lentils, grains, seeds such as flax, some fruits, and vegetables. Most dietary fibre is made up of cellulose, which humans are unable to digest. The bulk and soft texture of fibre helps to prevent constipation. Disorders of the Accessory Organs Two of the most serious disorders of the liver are hepatitis and cirrhosis, and both hepatitis inflammation are life-threatening. Hepatitis is an inflammation of the liver. There are three types of of the liver, most hepatitis: A, B, and C. Hepatitis A is usually contracted from drinking contaminated commonly caused water. Hepatitis B is spread by sexual contact but there is a vaccine to protect against it. by a virus Hepatitis C is usually contracted by contact with infected blood. There is no vaccine for cirrhosis the hepatitis C. irreversible replacement of healthy liver tissue Figure 10.16 shows part of the liver of someone who has cirrhosis—a chronic with non-functioning disease of the liver that occurs when scar tissue replaces healthy liver tissue and scar tissue; most prevents the liver from functioning properly. Chronic alcoholism and hepatitis C commonly caused by are the most common causes of cirrhosis of the liver. There are few symptoms in the excessive alcohol intake or hepatitis early stages of the disease. Blood tests, however, can determine if the liver is becoming fatty—an early warning sign that cirrhosis is developing. The liver has the ability to heal itself, but in many cases there is not enough regeneration to avoid liver failure. A liver transplant is the primary treatment for liver failure. Figure 10.16 (A) A normal, A B healthy human liver, and (B) a liver affected by cirrhosis. The word cirrhosis comes from the Greek word khirros, which means tawny, referring to the brownish-orange colour of the diseased liver. Another common disorder that affects the accessory organs is gallstones, which are small hard masses that form in the gall bladder. Remember that the gall bladder stores bile from the liver. Sometimes, cholesterol (a fat-like substance found in the blood and cells) in the bile can precipitate out of the bile and form crystals. The crystals grow and become gallstones. Factors that are related to the formation of gallstones are obesity, alcohol intake, and heredity. Gallstones are usually treated with medications or with ultrasound shock waves to disintegrate the stones so that they can be passed out in the urine. Since gallstones often reoccur, it is important to reduce the causal factors. Cholesterol in the gall bladder can be lowered by losing weight, increasing the intake of omega-3 fatty acids (unsaturated fats that are found in fish and nut oils), and decreasing the size of meals. If the gallstone problem is serious, the entire gall bladder may need to be surgically removed. Chapter 10 The Digestive System MHR 421  Learning Check 19. How do Helicobacter pylori cause the condition 23. Define the following disorders of the digestive shown in Figure 10.15? Explain your answer. system, and identify the causes of each. 20. Identify some lifestyle changes that can reduce the a. constipation risk of developing a gallstone. b. hepatitis 21. Why might Crohn’s disease be difficult to diagnose? c. cirrhosis 22. Distinguish between inflammatory bowel disease, 24. Why are coffee and citrus fruits, such as oranges Crohn’s disease, and ulcerative colitis, and describe and grapefruits, not recommended for patients in which part of the digestive tract each disease with ulcers? occurs. The Endoscope and Digestive System Disorders Modern technology allows surgeons to locate, diagnose, and remove ulcers, tumours, and other problems of the digestive tract without having to cut into the body of the patient. Recall that the alimentary canal is a tube running from the mouth to the anus. Therefore, physicians can get access to it through these natural openings at either end. A device used for this purpose is the endoscope. The endoscope often helps to confirm medical problems that are hard to observe using other methods, such as X rays. It allows a surgeon to visually inspect the lining of any part of the alimentary canal, including the stomach as shown in Figure 10.17 (A). Other attachments that can be fitted to the endoscope include a camera to photograph and record portions of the alimentary canal for further study; a laser that can be used to cut through tissue and seal blood vessels; and tiny forceps that can be used to extract samples of tissue for laboratory examination. A more recent development is the capsule endoscope, shown in Figure 10.17 (B)—a tiny camera placed inside a capsule that can be swallowed. The capsule endoscope is especially useful for seeing inside the small intestine, which is too long and coiled to allow an endoscope tube to be pushed through its entire length. Figure 10.17 (A) Doctors perform an endoscopy A B to examine a woman’s stomach and take a tissue sample (a biopsy). (B) The patient swallows a tiny capsule endoscope. Over the next eight hours, it travels down the digestive tract, where it takes about 30 pictures per second. Technologies such as endoscopy are known as non-invasive surgery, in contrast to traditional surgery in which a physician must cut into the body to repair or remove tissues and organs. Non-invasive surgery is relatively painless and allows patients to recover much faster than they do from traditional surgery. Complications from non-invasive surgery are rare. It can be carried out with only a local anesthetic, and it reduces the risk of infection. 422 MHR Unit 4 Animals: Structure and Function Diabetes Diabetes is a chronic disease in which body cells are unable to use glucose to provide diabetes a condition energy for muscles and tissues. Normally, the pancreas releases insulin into the in which the body is bloodstream after the individual has eaten. Insulin allows glucose from the digested unable to use glucose food to enter the body’s cells, and this lowers the amount of glucose circulating in the for energy bloodstream throughout the body. As the glucose level in the bloodstream drops, so does the release of insulin from the pancreas. As you learned earlier in the chapter, glycogen can be temporarily stored in the liver so that when the insulin level gets low—for example, when you have not eaten for a while—some of that stored glycogen is converted back to glucose to keep the blood glucose at a normal level. Diabetes develops when there is not enough insulin in the bloodstream or when the body cannot properly use the insulin that the pancreas makes. Without insulin, glucose cannot get into the cells and the glucose level in the blood can increase to life-threatening levels. The Three Types of Diabetes The three types of diabetes are type 1, type 2, and gestational diabetes. Type 1 diabetes occurs when the insulin-producing cells of the pancreas are destroyed by the immune system and therefore no longer produce insulin. Type 1 diabetes is most often diagnosed in children, teens, and young adults. Type 2 diabetes occurs when either the body does not make enough insulin or it is unable to properly use the insulin it makes. Although Type 2 diabetes is most often diagnosed in people over the age of 40, it is becoming increasingly common in children and adolescents. Gestational diabetes can develop during pregnancy. Even though this type of diabetes often ends when the baby is born, women who have had gestational diabetes are more likely to develop type 2 diabetes later in life. Gestational diabetes is often the result of pregnancy hormones or inadequate levels of insulin production. Canadian Contributions to Diabetes Research In 1922, Canadian scientists Frederick Banting and Charles Best, seen in Figure 10.18, discovered the connection between insulin and diabetes. Before then, diabetes usually resulted in early death. After Banting and Best demonstrated that insulin injections could help people with diabetes, the University of Toronto’s Connaught Laboratories developed ways