Chapter 21 Digestive System Introduction More than a

Chapter 21 Digestive System

Introduction • More than a third of American adults are obese (30 lbs+ overweight). • The obesity epidemic, combined with increasingly sedentary jobs and inactive lifestyles, has contributed to higher incidences of • • heart disease, diabetes, cancer, and other weight-related health problems. • More than 300, 000 deaths per year in the United States are attributed to weight-related issues.

Introduction As you think about your own weight and diet, you should begin with a clear understanding of the structure and function of your digestive system.

21. 1 Animals obtain and ingest their food in a variety of ways Most animals have one of three kinds of diets. 1. ______ eat plants and include cattle, gorillas, sea urchins, and snails. 2. _______ eat meat and include lions, owls, whales, and spiders. 3. _______ eat plants and other animals andinclude humans, roaches, raccoons, and crows.

21. 1 Animals obtain and ingest their food in a variety of ways • Animals obtain and ingest their food in different ways. • ______ feeders capture food particles from the surrounding medium. • ______ feeders live in or on their food source

_______ feeders suck nutrient-rich fluids from a living host. _______ feeders ingest large pieces of food.

21. 1 Animals obtain and ingest their food in a variety of ways Red pandas munch large quantities of bamboo, but also eat small mammals, birds, eggs, and berries. Name their diet category and type of feeding mechanism.

Video: Hydra Eating Daphnia What type of feeder? © 2018 Pearson Education, Inc.

Video: Shark Eating a Seal © 2018 Pearson Education, Inc.

21. 2 Overview: Food processing occurs in four stages • Food is processed in four stages: 1. 2. 3. 4. ______________ • Chemical digestion is necessary because animals cannot directly use the proteins, carbohydrates, fats, and nucleic acids in food. What are the two types of digestion that take place in your mouth?

Mechanical and Chemical Digestion Small molecules Pieces of food Mechanical digestion Chemical digestion (hydrolysis) Nutrient molecules enter body cells Undigested material 1 Ingestion © 2018 Pearson Education, Inc. 2 Digestion 3 Absorption 4 Elimination

Food is broken down (digested) into its components. • Proteins are broken down into ______. • Polysaccharides are broken down into _____ • Nucleic acids are broken down into ______ • Fats are broken down into ______ and ________

21. 3 Digestion occurs in specialized compartments Sponges (and protists) digest food in vacuoles.

• Most animals digest food in compartments. • Cnidarians and flatworms have a ______ cavity with a single opening, the mouth. • Most animals have an _______ canal that runs from mouth to anus with specialized regions along the way.

Tentacles 1 Enzymes released Mouth Food Gastrovascular cavity 2 Food broken down 3 Food particle engulfed 4 Particle digested in vacuole © 2018 Pearson Education, Inc.

Earthworm Mouth Anus Pharynx Esophagus Crop Intestine Gizzard Grasshopper Esophagus Midgut Anus Mouth Crop Gastric pouches Hindgut Bird Stomach Mouth Esophagus Crop Gizzard Intestine Anus © 2018 Pearson Education, Inc.

21. 4 The human digestive system consists of an alimentary canal and accessory organs • In humans, food is • ingested and chewed in the mouth, or oral cavity, • pushed by the tongue into the pharynx, • moved along through the alimentary canal by the rhythmic muscle contractions of ______, and • moved into and out of the stomach by ______.

• The final steps of digestion and nutrient absorption in humans occur in the ____ intestine. • Undigested material moves slowly through the _____ intestine and is then expelled through the anus.

21. 5 Digestion begins in the oral cavity • Mechanical digestion and chemical digestion begin in the mouth. • Chewing cuts, smashes, and grinds food, making it easier to swallow. • The tongue • tastes the food, • shapes the food into a ball called a _______, and • moves it toward the pharynx.

21. 6 After swallowing, peristalsis moves food through the esophagus to the stomach • The pharynx, or throat, opens to two passageways: • The swallowing reflex moves food into the esophagus and keeps it out of the trachea.

21. 7 The Heimlich maneuver can save lives • The Heimlich maneuver • involves a forceful elevation of the diaphragm, • pushes air into the trachea, and • can dislodge food from the pharynx or trachea during choking. • Brain damage or death will occur within minutes if no airway is open.

21. 8 The stomach stores food and breaks it down with acid and enzymes • The stomach secretes a digestive fluid called gastric juice, which is made up of: • ___________________ Pepsinogen (enzyme) and HCl are secreted in the stomach. HCl converts some pepsinogen to pepsin. Pepsin in gastric juice begins to digest protein.

Inside of stomach Esophagus Pits Sphincter Lumen (cavity) of stomach Stomach Gastrin Epithelium Mucous cells Gastric gland Chief cells Parietal cells © 2018 Pearson Education, Inc. 3 Pepsinogen Sphincter Small intestine Release of gastric juice (mucus, HCl, and pepsinogen) 1 2 HCl Pepsin (active enzyme)

21. 9 CONNECTION: Digestive ailments include acid reflux and gastric ulcers • Acid reflux, aka heartburn. • Gastroesophageal reflux disease (GERD) results from frequent and severe acid reflux that harms the lining of the esophagus. • Open sores in the lining of the stomach, called gastric ulcers, may form. • Bacterial infections (Helicobacter pylori) in the stomach and duodenum can produce ulcers.

21. 10 The small intestine is the major organ of chemical digestion and nutrient absorption • Emulsifiers from the liver/gallbladder • Enzymes from: • _______________ • Folds of the intestinal lining and finger-like _____ (with microscopic microvilli) increase the area across which absorbed nutrients move into capillaries and lymph vessels.

Where are each of these enzymes from? Which is not an enzyme? © 2018 Pearson Education, Inc.

Bile, made in the liver and stored in the gallbladder, emulsifies fat for attack by enzymes. Liver Bile Stomach Gallbladder Bile Chyme Intestinal enzymes Duodenum of small intestine © 2018 Pearson Education, Inc. Pancreas

Lumen of intestine Nutrient absorption Vein carrying blood to the liver Microvilli Amino Fatty acids and sugars glycerol Epithelial cells Lumen Muscle layers Large circular folds Villi Blood capillaries Nutrient absorption Fats Blood Lymph vessel Lymph Villi Intestinal wall © 2018 Pearson Education, Inc. Epithelial cells of a villus

21. 10 The small intestine is the major organ of chemical digestion and nutrient absorption At what point do food molecules actually enter the body’s cells?

21. 11 The liver processes and detoxifies blood from the intestines • Blood from the digestive tract drains into the _______ vein and then into the liver. • The liver regulates: • nutrient levels in the blood, • detoxifies alcohol and drugs, • and synthesizes blood proteins.

Between which two body systems does the liver act as a go-between? Heart Liver Intestines © 2018 Pearson Education, Inc. Hepatic portal vein

21. 12 The large intestine reclaims water and compacts the feces • The large intestine has a pouch called the ______ near its junction with the small intestine, which bears a small, finger-like extension, the ________. • Some bacteria in the colon produce vitamins. • The large intestine • absorbs these vitamins and water into the bloodstream, and • helps form firm feces, which are stored in the rectum until elimination.

Large intestine (colon) End of small intestine Unabsorbed food material Appendix Cecum © 2018 Pearson Education, Inc. Small intestine Rectum Anus

21. 12 The large intestine reclaims water and compacts the feces • Diarrhea occurs when too little water is reclaimed from the contents of the large intestine. • Constipation occurs when too much water is reclaimed. Explain why treatment with antibiotics for an extended period may cause a vitamin K deficiency.

21. 13 EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems relate to diet • The length of the digestive tract often correlates with diet. • Herbivores may have • longer alimentary canals than carnivores and • compartments that house cellulosedigesting microbes.

21. 14 An animal’s diet must provide sufficient energy • The diet must provide chemical energy (measured in kilocalories; 1 kcal = 1, 000 calories), raw materials for biosynthesis, and essential nutrients. • Metabolic rate, the rate of energy consumption, includes the basal metabolic rate (BMR) plus the energy used for other activities.

21. 15 An animal’s diet must supply essential nutrients • Essential nutrients are substances that an animal requires but cannot assemble from simple organic molecules. • Essential fatty acids, such as linoleic acid, are • used to make ______ of cell membranes and • found in seeds, grains, and vegetables. • Essential amino acids are • used to make ______ and • found in meats, eggs, milk, and cheese.

21. 16 A proper human diet must include sufficient vitamins and minerals • A vitamin is an organic molecule required in very small amounts in your diet. Most function as coenzymes. • Minerals are inorganic nutrients, required in small amounts, that play a variety of roles. • A varied diet usually meets the Recommended Dietary Allowances (RDAs) for these nutrients.

21. 17 CONNECTION: Food labels provide nutritional information • Food labels indicate • serving size, • calories per serving, • amounts of selected nutrients per serving and as a percentage of daily value, and • recommendations for daily limits of selected nutrients.

21. 18 CONNECTION: Dietary deficiencies can have a number of causes • Malnutrition, a diet insufficient in nutrients or calories, can cause significant health problems. • Protein deficiency is the most common cause of malnutrition worldwide. Does malnutrition always result from lack of access to food?

21. 19 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past • Obesity is defined as a too-high body mass index (BMI), a ratio of weight to height. • Obesity is linked to a lack of exercise and an abundance of fattening foods and may partly stem from an evolutionary advantage of fat hoarding. Why was fat hoarding essential?

21. 19 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past • The hormone leptin is produced by adipose (fat) cells and suppresses appetite. • Researchers discovered that mice who inherit a defect in the gene for leptin become very obese. • Obese children who have inherited a mutant form of the leptin gene lose weight after leptin treatments. But relatively few obese people have such deficiencies.

You should now be able to 1. Define and distinguish between herbivores, carnivores, omnivores, suspension feeders, substrate feeders, fluid feeders, and bulk feeders. 2. Describe the four stages of food processing. 3. Compare the structures and functions of a gastrovascular cavity and an alimentary canal. 4. Describe the specialized digestive systems of an earthworm, a grasshopper, and a bird.

You should now be able to 5. Describe the main components of the human alimentary canal and the associated digestive glands. 6. Describe the functional components of saliva and the types and functions of the teeth in humans. 7. Explain how swallowing occurs and how food is directed away from the trachea. 8. Explain how the Heimlich maneuver works.

You should now be able to 9. Relate the structure of the stomach to its functions. 10. Describe the causes and treatments of heartburn, GERD, and gastric ulcers. 11. Describe the different types of chemical digestion that occur in the small intestine. 12. Explain how the liver helps to regulate the chemical composition of blood.

You should now be able to 13. Describe the structures and functions of the colon and rectum. 14. Compare the digestive tracts of carnivores and herbivores. 15. List the three nutritional needs common to all animals.

a. g. b. h. c. d. i. e. j. k. f. l. © 2018 Pearson Education, Inc.