1 The Digestive System

Transcription

1 CHAPTER 24 1 The Digestive System SECTION The Digestive and Urinary Systems BEFORE YOU READ After you read this section, you should be able to answer these questions: What are the parts of the digestive system? How does each part of the digestive system work? National Science Education Standards LS 1a, 1d, 1e, 1f, 3b What Are the Parts of the Digestive System? The digestive system is a group of organs that break down, or digest, food so your body can get nutrients. The main organs of the digestive system make one long tube through the body. This tube is called the digestive tract. The digestive tract includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The digestive system has several organs that are not part of the digestive tract. The liver, gallbladder, pancreas, and salivary glands add materials to the digestive tract to help break down food. However, food does not go into these organs. The Digestive System Teeth Salivary glands STUDY TIP Organize As you read, make combination notes about each digestive organ. Write the function of the organ in the left column of the notes. Draw or describe the structure in the right column. 1. Identify What is the name of the tube that food passes through? Mouth Pharynx Esophagus Stomach Liver Gallbladder Pancreas Small intestine Large intestine Rectum Anus 2. Color Use a colored pencil to shade all of the digestive organs that food passes through. Interactive Textbook 383 The Digestive and Urinary Systems

2 STANDARDS CHECK LS 1e The human organism has systems for digestion, respiration, reproduction, circulation, excretion, movement, control and coordination, and protection from disease. These systems interact with one another. 3. Infer How does the circulatory system work with the digestive system? How Is Food Broken Down? The sandwich you eat for lunch has to be broken into tiny pieces to be absorbed into your blood. First, food is crushed and mashed into smaller pieces. This is called mechanical digestion. However, the food is still too large to enter your blood. Next, the small pieces of food are broken into their chemical parts, or molecules. This is called chemical digestion. The molecules can now be taken in and used by the body s cells. Most food is made up of three types of nutrients: carbohydrates, proteins, and fats. The digestive system uses proteins called enzymes to break your food into molecules. Enzymes act as chemical scissors to cut food into smaller particles that the body can use. What Happens to Food in the Mouth and Stomach? Critical Thinking 4. Infer Why do you think you should chew your food well before you swallow it? Math Focus 5. Compute Ratios Young children get a first set of 20 teeth called baby teeth. These teeth usually fall out and are replaced by 32 permanent teeth. What is the ratio of baby teeth to permanent teeth? MOUTH Digestion begins in the mouth where food is chewed. You use your teeth to mash and grind food. Chewing creates small, slippery pieces of food that are easy to swallow. As you chew, the food mixes with a liquid called saliva. Saliva is made in salivary glands in the mouth. Saliva has enzymes that start breaking down starches into simple sugars. Most adults have 32 permanent teeth. Each type of permanent tooth has a different role in breaking up food. Incisors Canine Premolars Molars ESOPHAGUS Once the food has been chewed to a soft mush, it can be swallowed. The tongue pushes the food into the pharynx. The pharynx is the part of the throat that makes food go to the esophagus and air go to the lungs. The esophagus is a long, straight tube that leads from the pharynx to the stomach. Muscle contractions, called peristalsis, squeeze food in the esophagus down to the stomach. Interactive Textbook 384 The Digestive and Urinary Systems

3 STOMACH The stomach is a muscular, saclike organ. The stomach uses its muscles to continue mechanical digestion. It squeezes and mashes food into smaller and smaller pieces. The stomach also has glands that make enzymes and acid. These chemicals help break down food into nutrients. Stomach acid also kills most bacteria in the food. After a few hours of chemical and mechanical digestion, the food is a soupy mixture called chyme. The stomach squeezes and mixes food for hours before it releases the mixture into the small intestine. 6. Identify What kinds of digestion occur in the stomach? Esophagus Stomach Part of small intestine What Happens to Food in the Small and Large Intestines? Most chemical digestion takes place after food leaves the stomach. Chyme slowly leaves the stomach and enters the small intestine. The pancreas, liver, and gallbladder add enzymes and other fluids to the small intestine to help finish digestion. The large intestine absorbs water and gets rid of waste. PANCREAS The pancreas is an organ located between the stomach and small intestine. Food does not enter the pancreas. Instead, the pancreas makes a fluid that flows into the small intestine. The chart below shows the chemicals that make up this pancreatic fluid, and the function of each. Chemical in pancreatic fluid sodium bicarbonate enzymes hormones Function to protect the small intestine from acid in the chyme to chemically digest chyme to control blood sugar levels 7. Identify What is the role of enzymes in pancreatic fluid? Interactive Textbook 385 The Digestive and Urinary Systems

4 LIVER The liver is a large, reddish brown organ found on the right side of the body under the ribs. The liver helps with digestion in the following ways. It makes bile. It stores extra nutrients. It breaks down toxins, such as alcohol. 8. Identify What is the function of bile? GALLBLADDER Bile is made in the liver, and stored in a small, saclike organ called the gallbladder. The gallbladder squeezes bile into the small intestine when there is food to digest. Bile breaks fat into very small droplets so that enzymes can digest it. The liver, gall bladder, and pancreas are linked to the small intestine. However, food does not pass through these organs. Liver Stomach Gallbladder 9. Identify Which organs in this diagram does food pass through? Pancreas Part of the small intestine 10. Explain Why is a large surface area in the small intestine important? SMALL INTESTINE The small intestine is a long, thin, muscular tube where nutrients are absorbed. If you stretched out your small intestine, it would be much longer than you are tall about 6 m! If you flattened out the surfaces of the small intestine, it would be larger than a tennis court. The inside wall of the small intestine is covered with many small folds. The folds are covered with cells called villi. Villi absorb nutrients. The large number of folds and villi increase the surface area of the small intestine. A large surface area helps the body get as many nutrients from food as possible. Interactive Textbook 386 The Digestive and Urinary Systems

5 The inside of the small intestine is folded. The folds are covered with finger-like structures called villi. 11. Explain How do nutrients get into the bloodstream? Villi are covered with cells that absorb nutrients and pass them to the bloodstream. Most nutrient molecules are taken into the blood from the small intestine. However, the body can t use everything you eat. The soupy mixture of water and food that cannot be absorbed moves into the large intestine. LARGE INTESTINE The large intestine is the last part of the digestive tract. It stores, compacts, and rids the body of waste. The large intestine is wider than the small intestine, but shorter. It takes most of the water out of the mixture from the small intestine. By removing water, the large intestine changes the liquid into mostly solid waste called feces, or stool. The rectum is the last part of the large intestine. The rectum stores feces until your body can get rid of them. Feces leave the body through an opening called the anus. It takes about 24 hours for food to make the trip from your mouth to the end of the large intestine. You can help keep your digestive system healthy by eating whole grains, fruits, and vegetables. These foods contain a carbohydrate called cellulose, or fiber. Humans cannot digest fiber. However, fiber keeps the stool soft and keeps materials moving well through the large intestine. Say It Name With a partner, name as many foods as you can that are sources of fiber. Interactive Textbook 387 The Digestive and Urinary Systems

6 Section 1 Review NSES LS 1a, 1d, 1e, 1f, 3b SECTION VOCABULARY digestive system the organs that break down food so that it can be used by the body esophagus a long, straight tube that connects the pharynx to the stomach gallbladder a sac-shaped organ that stores bile produced by the liver large intestine the wider and shorter portion of the intestine that removes water from mostly digested food and that turns the waste into semisolid feces, or stool liver the largest organ in the body; it makes bile, stores and filters blood, and stores excess sugars as glycogen pancreas the organ that lies behind the stomach and that makes digestive enzymes and hormones that regulate sugar levels small intestine the organ between the stomach and the large intestine where most of the breakdown of food happens and most of the nutrients from food are absorbed stomach the saclike, digestive organ between the esophagus and the small intestine and that breaks down food by the action of muscles, enzymes, and acids 1. List What organs in the digestive system are not part of the digestive tract? 2. Describe What is the function of saliva? 3. Compare How is chemical digestion different from mechanical digestion? 4. List Name three places in the digestive tract where chemical digestion takes place. 5. Explain How does the structure of the small intestine help it absorb nutrients? 6. Apply Concepts How would digestion change if the liver didn t make bile? Interactive Textbook 388 The Digestive and Urinary Systems

7 Life Science Answer Key continued 3. blood plasma, dead cells, pathogens 4. Lymph tissue must be spread out to collect fluid from all areas of the body. SECTION 4 THE RESPIRATORY SYSTEM 1. the way your body gains and uses oxygen and gets rid of carbon dioxide 2. nose, pharynx, larynx, trachea, lung, bronchus, diaphragm 3. It is the main passageway into and out of the respiratory system. 4. the main passageway to the lungs 5. alveoli 6. The person would be unable to inhale. 7. Oxygen moves into the alveoli in the lungs. Then it moves into the blood in the capillaries. It moves from the blood into the other cells in your body. Review 1. asthma, emphysema, SARS 2. Cellular respiration is the process in which cells use oxygen to break down glucose. The process produces carbon dioxide. 3. Breathing involves only inhaling and exhaling. Respiration involves everything that allows your body to take in oxygen, use it for energy production, and get rid of carbon dioxide. 4. Air can also enter and leave through the mouth. 5. The vocal cords stretch across the larynx. When air moves over them, they vibrate and produce sound. 6. A respiratory disorder can prevent a person from getting enough oxygen. It can also prevent the person from getting rid of enough carbon dioxide. Chapter 24 The Digestive and Urinary Systems THE DIGESTIVE SYSTEM 1. digestive tract 2. The mouth, pharynx, esophagus, stomach, small intestine, and large intestine should be shaded. 3. The digestive system breaks down food into molecules that are absorbed by the blood in the circulatory system. 4. Chewing helps break your food into smaller pieces and helps mix the food with saliva. 5. 5:8 6. mechanical and chemical 7. to chemically digest chyme 8. to break down fat into small droplets 9. stomach and small intestine 10. A large surface area lets the small intestine absorb as many nutrients from food as possible. 11. They are absorbed by villi and passed into the bloodstream. Review 1. liver, gallbladder, salivary glands, pancreas 2. Saliva has enzymes that start the breakdown of starches into simple sugars. 3. In mechanical digestion, food is broken, crushed, or mashed. In chemical digestion, large food molecules are broken down into nutrients. 4. mouth, stomach, small intestine 5. The small intestine is long, with folds and cells that absorb nutrients. These give the small intestine a large surface area so more nutrients can be taken into the blood. 6. If the liver did not make bile, fats would not be digested well. There would also be nothing to store in the gallbladder. SECTION 2 THE URINARY SYSTEM 1. the kidneys 2. From top to bottom: ureter, urinary bladder 3. about 350 times 4. The blood flows back to the body. 5. ureters 6. The nephrons do not put as much water back into the blood. You make more urine. 7. They can block the flow of urine and cause pain. Review 1. kidneys, ureters, urinary bladder, urethra 2. b. Blood goes into the kidney. c. Water and waste go into the nephron. d. Nephrons separate water and waste. a. Water is put back in the blood. 3. The blood leaving the kidney has less water. The nephrons have to take some water from the blood to produce urine. Interactive Textbook Answer Key 27 Life Science