Chapter 36 Digestion and Human Nutrition (Sections 36.1 - 36.6)

1. Chapter 36Digestion and Human Nutrition(Sections 36.1 - 36.6)

2. 36.1 The Battle Against Bulge • When you eat more food than you need, you store the excess energy – mostly as fat in adipose tissue • In the US about two-thirds of adults are overweight or obese, which increases risk of type 2 diabetes, cardiovascular disease, some cancers, and other disorders • Increasing portion sizes and fast-food meals contribute to the obesity trend in adults and children

3. Battle Against Bulge (cont.) • Genetics contribute to weight control • The ob gene encodes a hormone (leptin) made by adipose cells that suppresses appetite – people who can’t make leptin are severely obese • Another obesity-related gene, fto, affects food intake – people with the high-risk allele eat more food before they feel full

4. Effects of a Mutant ob Gene

5. ABC Video: Diet Soda and Weight Gain

6. 36.2 Animal Digestive Systems • Animals are heterotrophs that typically digest food inside their body, but outside of their cells • The digestive system mechanically and chemically breaks food down to molecules that are absorbed into the internal environment, and expels unabsorbed residues • The digestive system interacts with other organ systems to maintain homeostasis for the body as a whole

7. Incomplete and Complete Systems • Some invertebrates have an incomplete digestive system, but most invertebrates and all vertebrates have a complete digestive system • incomplete digestive system • Saclike digestive system; food enters and leaves through the same opening • complete digestive system • Tubelike digestive system; food enters through one opening and wastes leave through another

8. Incomplete Digestive System

9. Incomplete Digestive System branching saclike gut single opening takes in food, expels waste pharynx A Incomplete digestive system of a flatworm. Fig. 36.2a, p. 596

10. Complete Digestive System

11. Complete Digestive System esophagus pharynx stomach mouth with tongue small intestine large intestine cloaca (opening through which digestive wastes, urinary wastes, and gametes exit the body) liver gallbladder pancreas B Complete digestive system of a frog. Fig. 36.2b, p. 596

12. Five Tasks of the Digestive System 1. Mechanical processing and motility: • Movements that break up, mix, and directionally propel food material 2. Secretion: • Release of substances, especially digestive enzymes, into the lumen (the space inside the tube) 3. Digestion: • Breakdown of food into particles, then to nutrient molecules small enough to be absorbed

13. Five Tasks of the Digestive System 4. Absorption: • Uptake of digested nutrients and water across the gut wall, into extracellular fluid 5. Elimination: • Expulsion of undigested or unabsorbed solid residues

14. Diet-Related Structural Adaptations • Features of an animal digestive systems are shaped by natural selection and adapt the animal to a particular diet • A bird’s beak-size and shape determines what kinds of food it can process • Teeth of mammals differ, depending on their diet: • Carnivores have long, sharp canine teeth • Herbivores (e.g. antelopes) have prominent incisors for grazing, and flat molars for grinding food

15. Herbivore and Human Molars

16. Herbivore and Human Molars gumline crown root antelope molar crown root human molar Fig. 36.3a, p. 597

17. Diet-Related Adaptations (cont.) • Animal guts also are specialized to their diets • Seed-eating birds have a large crop for storing food; and a large, tough gizzard for grinding food

18. Diet-Related Adaptations (cont.) beak mouth esophagus crop glandular part of stomach gizzard intestines cloaca C Complete digestive system of a bird. The crop is an expandable organ for storing food. The muscular gizzard grinds up food. Fig. 36.2c, p. 596

19. ANIMATION: Examples of digestive systems To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

20. Diet-Related Adaptations (cont.) • Ruminantshave multiple stomach chambers that maximize nutrients extracted from plant foods rich in cellulose • Microbes ferment cellulose in the first two chambers • Solids in the second chamber form “cud” that is regurgitated for a second chewing • ruminant • Hoofed mammal with a multiple-chamber stomach that adapts it to a cellulose-rich diet

21. A Ruminant Stomach

22. A Ruminant Stomach ingestion, regurgitation, reswallowing of food through esophagus stomach chamber 1 stomach chamber 2 stomach chamber 3 stomach chamber 4 to small intestine B Fig. 36.3b, p. 597

23. ANIMATION: Antelope stomach function To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

24. Diet-Related Adaptations (cont.) • Some meat-eaters have stomachs that can stretch enormously – a python may eat only once or twice a year

25. Key Concepts • Animal Digestive Systems • Some animal digestive systems are saclike, but most are a tube with two openings • The structure of an animal’s digestive system often reveals adaptations that allow the animal to eat a specific diet • For example, antelopes have adaptations that allow them to eat grasses

26. 36.3 The Human Digestive System • Humans have a complete digestive system with specialized regions for digesting food, absorbing nutrients, and concentrating and storing unabsorbed waste • Salivary glands, the pancreas, and the liver are accessory organs that secrete enzymes and other substances into the tubular portion of this system

27. Overview of the Digestive System • Food taken into the human mouth is swallowed and moves into the pharynx, which opens onto the esophagus • Peristalsisof the esophagus conveys food to the stomach • From the stomach, food enters the small intestine, then the large intestine (colon) • Wastes are stored in the rectumuntil they are eliminated through the anus

28. Key Terms • esophagus • Muscular tube between the throat and stomach • peristalsis • Wavelike smooth muscle contractions that propel food through the digestive tract • stomach • Muscular organ that mixes food with acid and digestive enzymes (gastric fluid) that it secretes

29. Key Terms • small intestine • Longest portion of the digestive tract • Receives secretions from the liver and pancreas • Site of most digestion and absorption • colon (large intestine) • Receives digestive waste from the small intestine and concentrates it as feces • Absorbs water and ions

30. Key Terms • rectum • Region where feces are stored prior to excretion • anus • Opening through which digestive waste is expelled from a complete digestive system

31. Major Organs and Accessory Organs

32. A Major Organs B Accessory Organs Mouth Oral cavity. Teeth break food into bits. Tongue mixes food with saliva. Salivary Glands Produce and secrete saliva, which moistens food and begins the process of carbohydrate digestion. Pharynx (throat) Entrance to the gut and respiratory system. Action of the epiglottis keeps food from entering the trachea. Esophagus Muscular tube through which food moves to the stomach. Liver Produces bile, which aids digestion and absorption of fats. Stomach J-shaped muscular sac that receives food and mixes it with gastric fluid secreted by cells in its lining. Gallbladder Stores and concentrates bile, then secretes it into the small intestine. Small Intestine Longest tube of the gut. Its first part receives secretions from the liver, gallbladder, and pancreas. These secretions help complete the process of digestion. Most water and products of digestion are absorbed across the highly folded wall of this organ. Pancreas Secretes enzymes and bicarbonate (a buffer) into the small intestine. Large Intestine (colon) Wider than the small intestine, but shorter. It absorbs most remaining water, thus concentrating any undigested waste and forming the feces. Major Organs and Accessory Organs Rectum Expandable sac that stores feces. Anus Opening through which feces are expelled from the body. Fig. 36.5, p. 598

33. ANIMATION: Human digestive system To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

34. Key Concepts • Human Digestive System • In humans, food taken into the mouth is mechanically broken down by teeth • Saliva starts the process of chemical digestion • The stomach stores and digests food • Digestion is completed and absorption begins in the small intestine • The large intestine concentrates wastes

35. ANIMATION: Digestion To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

36. 36.4 Digestion in the Mouth • Mechanical digestion begins in the mouth when teeth break food into smaller pieces • Human adults have four types of teeth: incisors, canines, premolars, and molars • Each tooth consists of bonelike dentin, with a crown covered by enamel, the hardest material in the body

37. Human Teeth

38. Human Teeth Fig. 36.6a, p. 599

39. Human Teeth A Adult teeth. Incisors shear off bits of food. Canines tear meats. Premolars and molars have broad, bumpy crowns that are platforms for grinding and crushing food. molars (12) premolars (8) canines (4) incisors (8) lower jaw upper jaw Fig. 36.6a, p. 599

40. Human Teeth Fig. 36.6b, p. 599

41. Human Teeth B Cross-section of one human tooth. The crown is the portion extending above the gum; the root is embedded in the jaw. enamel crown dentin pulp cavity (contains nerves and blood vessels) gingiva (gum) ligaments root root canal periodontal membrane bone Fig. 36.6b, p. 599

42. Digestion in the Mouth (cont.) • Chemical digestion (enzymatic breakdown of food into molecular subunits) also begins in the mouth • Saliva, secreted by salivary glands, contains enzymes, bicarbonate, and mucins • Salivary amylase begins breakdown of starch; salivary lipase begins breakdown of fats • salivary gland • Exocrine gland that secretes saliva into the mouth

43. 3D Animation: Digestive Motility

44. 36.5 Food Storage and Digestion in the Stomach • The stomach is a muscular, highly-folded, stretchable sac with a sphincter at either end • It stores food and continues the process of digestion that began in the mouth • sphincter • Ring of muscle that controls passage through a tubular organ or body opening

45. Structure of the Stomach

46. Structure of the Stomach gastroesophageal sphincter esophagus serosa longitudinal muscle circular muscle pyloric sphincter oblique muscle submucosa small intestine mucosa Fig. 36.7, p. 600

47. Functions of the Stomach • The stomach has three functions: • It stores food and controls the rate of passage to the small intestine • It mechanically breaks down food • It secretes substances that aid in chemical digestion

48. Digestion in the Stomach • Cells of the glandular epithelium (mucosa) lining the stomach secrete gastric fluid, which includes mucus, hydrochloric acid, and pepsinogen, an inactive form of the protein-digesting enzyme pepsin • gastric fluid • Fluid secreted by the stomach lining • Contains digestive enzymes, acid, and mucus

49. Digestion in the Stomach (cont.) • Action potentials generated in the upper portion of the stomach cause rhythmic stomach contractions that mix gastric fluid with food to form chyme • chyme • A semiliquid mixtureof food and gastric fluid

50. Chemical Digestion of Protein • Arrival of food in the stomach triggers endocrine cells to secrete gastrin into the blood, which stimulates acid secretion by cells of the stomach lining • Acid in denatures proteins and exposes their peptide bonds • Acids also converts pepsinogen into pepsin, which breaks peptide bonds, cutting proteins into smaller polypeptides