Nutrition, Digestion, and Absorption

1. 39 Nutrition, Digestion, and Absorption

2. Chapter 39 Nutrition, Digestion, and Absorption • Key Concepts • 39.1 Food Provides Energy and Nutrients • 39.2 Digestive Systems Break Down Macromolecules • 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • 39.4 Food Intake and Metabolism Are Regulated

3. Chapter 39 Opening Question Why are some ethnic groups of humans much more prone to obesity and diabetes than other groups?

4. Concept 39.1 Food Provides Energy and Nutrients • Animals are heterotrophs and derive their nutrition by eating other organisms. • Autotrophs use solar energy or inorganic chemical energy to synthesize their necessary nutrients. • Heterotrophs depend on this synthesis and have adapted to take advantage of it.

5. Figure 39.1 Heterotrophs Get Energy from Autotrophs (Part 1)

6. Figure 39.1 Heterotrophs Get Energy from Autotrophs (Part 2)

7. Concept 39.1 Food Provides Energy and Nutrients • Energy needs can be measured. • Measures of heat energy: • A calorie is the amount of heat needed to raise 1 gram of water 1°C • A kilocalorie(kcal) = 1,000 calories • The Calorie (Cal) is the same as a kilocalorie and = 1,000 calories • A joule = 0.239 calories

8. Concept 39.1 Food Provides Energy and Nutrients • The metabolic rate measures energy needs of an animal that are met by food intake and digestion. • Foods that provide energy are fats, carbohydrates, and proteins. • Basal metabolic rate (BMR) is the minimum energy needed to sustain life while an animal is at rest.

9. Concept 39.1 Food Provides Energy and Nutrients • Animals must store food between meals. • Carbohydrates are stored in liver and muscle cells as glycogen—enough for about a day’s energy needs. • Most fuel is stored as fat—stores more energy per gram and with little water, which makes it more compact.

10. Concept 39.1 Food Provides Energy and Nutrients • Essential nutrients are required but cannot be synthesized. • Macronutrients—nutrients required in large amounts, like calcium • Micronutrients—nutrients required in tiny amounts, like iron • Amino acids are the building blocks of proteins. • Each species has essential amino acids that they cannot synthesize.

11. Concept 39.1 Food Provides Energy and Nutrients • Complementary diets can supply all eight essential amino acids for adult humans. • Humans must also obtain essential fatty acids. • Linoleic acid is one that helps synthesize other unsaturated fatty acids.

12. Figure 39.2 A Strategy for Vegetarians

13. Concept 39.1 Food Provides Energy and Nutrients • An essential mineral is a chemical element required in the diet. • Calcium is a macronutrient, important in structure of bones and teeth and nerve and muscle function. • Osteoporosis is due to insufficient calcium. • Iron is a micronutrient, important in blood and enzyme structure. • Iron-deficiency anemia—too few red blood cells—is common.

14. Table 39.1 Mineral Elements Required by Animals

15. Concept 39.1 Food Provides Energy and Nutrients • Vitamins—carbon compounds that are micronutrients • Species-specific, some can be synthesized • Scurvy—lack of vitamin C—cured by ascorbic acid in citrus fruits • Vitamins are water- or fat-soluble. Excess water-soluble ones are excreted in the urine—fat-soluble ones like Vitamin D may build up in the liver.

16. Table 39.2 Vitamins in the Human Diet

17. Concept 39.1 Food Provides Energy and Nutrients • Nutrient deficiency leads to malnutrition—chronic malnutrition leads to a deficiency disease: • Scurvy and anemia • Beriberi—due to deficiency of B1 • Goiter and hypothyroidism—due to iodine deficiency

18. Concept 39.2 Digestive Systems Break Down Macromolecules • The function of the digestive system, or gut, is to break down food into molecules for absorption. • Food is broken down through hydrolysis by enzymes produced by the digestive system. • Enzymes are classified by the food they break down: proteases, carbohydrases, peptidases, lipases, and nucleases.

19. Concept 39.2 Digestive Systems Break Down Macromolecules • Digestion usually begins in a body cavity. • Gastrovascular cavities connect to the outside through a single opening. • Example: A jellyfish stings prey and brings it into its gastrovascular cavity—enzymes break down food, and undigested particles are released through the same opening.

20. Concept 39.2 Digestive Systems Break Down Macromolecules • Tubular guts have an opening at each end: • A mouth takes in food, molecules are digested, and wastes are eliminated through the anus. • In most animals the gut can be divided into three sections: foregut, midgut, and hindgut.

21. Figure 39.3 Compartments for Digestion and Absorption (Part 1)

22. Figure 39.3 Compartments for Digestion and Absorption (Part 2)

23. Figure 39.3 Compartments for Digestion and Absorption (Part 3)

24. Concept 39.2 Digestive Systems Break Down Macromolecules • Food is broken up in the mouth cavity by teeth, radula (snails), ormandibles (arthropods). • From the mouth the food moves through an esophagus to a stomach, or storage sac. • Some animalshave two organs in a row—a crop that holds food and a muscular gizzard that grinds up food.

25. Concept 39.2 Digestive Systems Break Down Macromolecules • Small food particles are delivered into the midgut—a long thin midgut is the small intestine. • Nutrients are absorbed in the midgut through villi—fingerlike projections that increase surface area for absorption. • Villi have microvilli to provide even more surface area.

26. Figure 39.4 Intestinal Surface Area and Nutrient Absorption (Part 1)

27. Figure 39.4 Intestinal Surface Area and Nutrient Absorption (Part 2)

28. Figure 39.4 Intestinal Surface Area and Nutrient Absorption (Part 3)

29. Concept 39.2 Digestive Systems Break Down Macromolecules • The hindgut, or large intestine, recovers ions and water and stores undigested waste as feces. • The end of the digestive tract is the anus. • In birds, amphibians and reptiles, the cloaca expels both urinary and digestive wastes. • Most digestive tracts contain symbiotic bacteria.

30. Concept 39.2 Digestive Systems Break Down Macromolecules • Heterotrophs can be classified by how they acquire food: • Saprobes (decomposers) absorb nutrients from dead organic matter. • Detritivores actively feed on dead organic matter. • Predators feed on living organisms.

31. Concept 39.2 Digestive Systems Break Down Macromolecules • Predators feed on other animals: • Herbivores—consume plants • Carnivores—prey on animals • Omnivores—prey on both • Filter feeders filter small organisms from an aquatic environment • Fluid feeders include mosquitoes

32. Concept 39.2 Digestive Systems Break Down Macromolecules • Mammalian teeth have shapes and organization adapted to specific diets: • Incisors—used for cutting, chopping, or gnawing • Canines—for stabbing, gripping, or ripping • Molars or premolars—shearing, crushing, or grinding

33. Figure 39.5 Mammalian Teeth

34. Concept 39.2 Digestive Systems Break Down Macromolecules • Diet affects the size of the digestive system. • Carnivores have short digestive tracts, because meat is easy to digest. • Herbivores have longer digestive tracts, often with compartments for cellulose-digesting bacteria to aid in plant digestion. • Traits in humans indicate we are omnivores.

35. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • The vertebrate digestive system is a tubular gut, running from mouth to anus. • It has several accessory glands, including liver and pancreas. • Processes occur in sequence in different sections.

36. Figure 39.6 The Vertebrate Digestive System

37. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • The vertebrate gut has a layered plan: • Lumen—the gut cavity • Mucosa—layer of epithelial cells, mucosal epithelium, that secrete mucus, digestive enzymes, or hormones; some absorb nutrients through microvilli • The submucosahas blood and lymph vessels, and nerves

38. Figure 39.7 Tissue Layers of the Vertebrate Gut

39. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Two layers of smooth muscle are outside the submucosa: • The circular muscle layer—innermost cells oriented around the gut that constrict the gut • The longitudinal muscle layer—outermost cells oriented along the gut that shorten the gut

40. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Between layers of smooth muscle are nerves that coordinate movement of the gut. • Nerves in the enteric nervous system only form synapses with other nerves in the network. • The peritoneum is a membrane that surrounds the gut and lines the wall of the cavity.

41. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • In mammals, digestion begins in the mouth—chewing mixes food with saliva, containing amylase to digest starch. • A mouthful of food is a bolus—when swallowed it passes into theesophagus. • Food is kept out of the trachea by the epiglottis, which closes off the larynx. • The bolus moves toward the stomach through peristalsis, coordinated by an anticipatory wave of relaxation.

42. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • The stomach holds large amounts of food, breaks it up, and begins protein digestion. • Gastric pits in the stomach are lined with three types of secretory cells: • Chief cells • Parietal cells • Mucus-secreting cells

43. Figure 39.8 Action in the Stomach (Part 1)

44. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Chief cells secrete pepsinogen, the inactive form of a proteolytic enzyme, pepsin. • Parietal cells secrete hydrochloric acid (HCl), which kills ingested organisms, breaks down food, and activates pepsin. • Newly active pepsin activates other pepsinogen molecules—a process called autocatalysis. • Mucus-secreting cells protect the stomach from the formation of ulcers.

45. Figure 39.8 Action in the Stomach (Part 2)

46. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Parietal cells produce HCl and keep the stomach pH below 1. • They contain carbonic anhydrase, which catalyzes the formation of H2CO3 from CO2; H2CO3 dissociates into HCO3–and H+. • One antiporter exchanges HCO3– for Cl– and another exchanges H+ ions for K+. • K+ leaks back into the cells and H+ is continually returned to the stomach.

47. Figure 39.8 Action in the Stomach (Part 3)

48. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Smooth muscle contractions in the stomach create chyme—a mixture of gastric juice and partly digested food. • The stomach walls contract and move chyme to the bottom of the stomach. • The pyloric sphincter allows small amounts to enter the small intestine.

49. Concept 39.3 The Vertebrate Digestive System Is a Tubular Gut with Accessory Glands • Ruminants have four-chambered stomachs: • The rumen and reticulum contain microorganisms that metabolize the cellulose into nutrients for the host. • Food then travels to the omasum where it is concentrated by water absorption. • The abomasum is the true stomach. • Microorganisms are also digested by the host and provide protein.

50. Figure 39.9 A Ruminant’s Stomach