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CHAPTER 21 Nutrition and Digestion
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CHAPTER 21 Nutrition and Digestion

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  1. CHAPTER 21Nutrition and Digestion

  2. Getting Their Fill of Krill • Animals obtain and process nutrients in a variety of ways • Humpback whales eat small fishes and crustaceans called krill • This painting shows how the whales corral their food using “bubble nets”

  3. When they feed, they take in large amounts of seawater in which the fish and krill live • They must filter out the water in order to get a meal • Humpback whales strain their food from seawater using large, brushlike plates called baleen

  4. They store the excess energy they harvest in the form of blubber • In about 4 months, a humpback whale eats, digests, and stores as fat enough food for an entire year • In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill

  5. OBTAINING AND PROCESSING FOOD 21.1 Animals ingest their food in a variety of ways • Animal diets are highly varied • Herbivores are plant-eaters • Carnivores are meat-eaters • Omnivores eat both plants and other animals Figure 21.1A

  6. Most animals ingest chunks of food Figure 21.1E

  7. Some animals are suspension feeders, consuming particles from water • Some are substrate feeders, living in or on their food source Figure 21.1B, C

  8. Some are fluid feeders, sucking liquids Figure 21.1D

  9. Choanocyte incontact withan amoebocyte • Flagellated choanocytes filter food from the water passing through the porous body Pores WATERFLOW Skeletalfiber Centralcavity Choanocyte Flagella Amoebocyte Figure 18.3C

  10. Capsule(nematocyst) Coiledthread Tentacle “Trigger” Dischargeof thread Prey CNIDOCYTE Figure 18.4D

  11. 18.6 Flatworms are the simplest bilateral animals • Phylum Platyhelminthes • Planarians have a simple nervous system consisting of a brain, sense organs, and branching nerves • As in cnidarians, the mouth of a flatworm is the only opening for its gastrovascular cavity Digestive tract(gastrovascularcavity) Nerve cords Mouth Eyespots Nervoustissue clusters Figure 18.6A Bilateral symmetry

  12. VISCERAL MASS Coelom Reproductiveorgans Kidney Heart Digestivetract MANTLE Shell Mantlecavity Radula RADULA Anus Gill Mouth FOOT Nervecords Mouth Figure 18.9A

  13. Most leeches are free-living carnivores, but some suck blood Figure 18.11C

  14. The water vascular system has suction-cup-like tube feet used for respiration and locomotion Anus Spines Stomach TUBE FEET CANALS Figure 18.14A

  15. 21.2 Overview: Food processing occurs in four stages Smallmolecules Piecesof food Nutrientmoleculesenter body cells Chemical breakdown(enzymatic hydrolysis) Mechanicalbreakdown Undigestedmaterial Food 1 3 4 2 ELIMINATION INGESTION DIGESTION ABSORPTION Figure 21.2

  16. 21.3 Digestion occurs in specialized compartments • Food is digested in compartments housing hydrolytic enzymes • Most animals have a specialized digestive tract

  17. This is called a gastrovascular cavity • Example: hydra • Relatively simple animals have a sac with a single opening Mouth Tentacle Hydrolyticenzymes Flagella Foodparticle Engulfmentof foodparticle Food(Daphnia,a waterflea) Gastro-vascularcavity Digestion infood vacuole Figure 21.3A

  18. This is a tube running from mouth to anus • This tube is divided into specialized regions that process food sequentially • In most animals, the digestive compartment is an alimentary canal Crop Gizzard Esophagus Intestine Pharynx Anus Mouth EARTHWORM Wall of intestine Interior of intestine Figure 21.3B

  19. Esophagus Stomach Gizzard Anus Esophagus Stomach Gizzard Intestine Crop Intestine Gastric pouches Mouth Mouth GRASSHOPPER Crop Anus BIRD Figure 21.3B (cont)

  20. HUMAN DIGESTIVE SYSTEM 21.4 The human digestive system consists of an alimentary canal and accessory glands • When food is swallowed, it is moved through the alimentary canal by peristalsis • Peristalsis is rhythmic muscle contraction in the walls of the digestive tract • Ringlike sphincter muscles regulate the passage of food

  21. Oral cavity Mouth Tongue Pharynx Salivaryglands Esophagus Liver Stomach Pyloricsphincter Stomach Gall-bladder Smallintestine Pancreas Smallintestine Largeintestine Rectum Figure 21.4 Anus

  22. 21.5 Digestion begins in the oral cavity • The teeth break up food • Saliva moistens it • Salivary enzymes begin the hydrolysis of starch • The tongue pushes the chewed food into the pharynx

  23. TEETH Incisors Canine Premolars Molars “Wisdom”tooth Tongue Salivaryglands Opening of asalivary gland duct Figure 21.5

  24. 21.6 The food and breathing passages both open into the pharynx • The swallowing reflex moves food from the pharynx into the esophagus • At the same time, food is kept out of the trachea

  25. Bolus of food Tongue Epiglottisup Epiglottisdown Pharynx Larynx Esophagealsphincter Larynxdown Larynxup Trachea(windpipe) Esophagus Esophagus Sphincter relaxed Sphincter contracted Sphincter contracted Figure 21.6

  26. 21.7 The esophagus squeezes food along to the stomach • Peristalsis in the esophagus moves food boluses into the stomach Relaxedmuscles Circularmuscle layer Circularmusclescontract,constrictingpassagewayand pushingbolus down Relaxedmuscles Bolus offood Longitudinalmusclescontract,shorteningpassagewayahead of bolus Stomach Longitudinalmuscle layer Figure 21.7

  27. 21.8 The stomach stores food and breaks it down with acid and enzymes • The stomach mixes food with gastric juice • The gastric juice contains pepsin, which begins the hydrolysis of protein

  28. Interior surfaceof stomach Pits Gastric juice(mucus, HCI,and pepsinogen) Food particle 3 Epithelium Gastricjuice Pepsinogen Pepsin (activeenzyme) 2 Mucouscells HCI Pyloricsphincter 1 Gastricgland STOMACH Chief cells Pariental cells Figure 21.8

  29. 21.9 Connection: Bacterial infections can cause ulcers • New evidence suggests that a spiral-shaped prokaryote causes gastric ulcers • Helicobacter pylori growth erodes protective mucus and damages the stomach lining

  30. 21.10 The small intestine is the major organ of chemical digestion and nutrient absorption • Alkaline pancreatic juice neutralizes stomach acids • Its enzymes digest polysaccharides, proteins, nucleic acids, and fats • Bile emulsifies fat droplets for attack by pancreatic enzymes • It is made in the liver and stored in the gall bladder

  31. Bile Liver Stomach Gall-bladder Acid chyme Bile Duodenum ofsmall intestine Pancreas Figure 21.10A

  32. Enzymes from the walls of the small intestine complete the digestion of many nutrients Table 21.10

  33. Villi increase the absorptive surface • Nutrients pass through the epithelium of the villi and into the blood • The blood flows to the liver • The liver can store nutrients and convert them to other substances the body can use • The lining of the small intestine is folded and covered with tiny, fingerlike villi

  34. INTERIOR OF INTESTINE Blood vesselwith blooden route tothe liver Nutrientabsorption Nutrientabsorption Microvilli Epithelialcells Lumen Musclelayers Bloodcapillaries Circular folds Villi Lymphvessel EPITHELIALCELLS Nutrientabsorption VILLI INTESTINAL WALL Figure 21.10B

  35. 21.11 The large intestine reclaims water Largeintestine(colon) • Undigested material passes to the large intestine, or colon • Water is absorbed • Feces are produced Endof smallintestine Small intestine Rectum Anus Nutrientflow Appendix Cecum Figure 21.11

  36. DIETS AND DIGESTIVE ADAPTATIONS 21.12 Adaptations of vertebrate digestive systems reflect diet • Herbivores and omnivores generally have longer alimentary canals than carnivores • Plant matter is more difficult to digest than meat • Nutrients in vegetation are less concentrated than in meat

  37. Small intestine Smallintestine Stomach Cecum Colon(largeintestine) Figure 21.12A CARNIVORE HERBIVORE

  38. The cecum is a pouch where the large and small intestines connect • Examples: horses and elephants • Other mammals re-ingest their feces to recover nutrients • Examples: rabbits and some rodents • Some mammals house cellulose-digesting microbes in the colon or cecum

  39. Intestine 3 1 Omasum Rumen • Ruminants such as cows process cellulose in a four-chambered stomach Esophagus 2 Rumen Reticulum 4 Abomasum Figure 21.12B

  40. NUTRITION 21.13 Overview: A healthful diet satisfies three needs • An animal’s diet provides • fuel for its activities • raw materials for making the body’s own molecules • essential nutrients that the body cannot make

  41. 21.14 Chemical energy powers the body • Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy • This energy is in the form of ATP

  42. The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR) Figure 21.14

  43. More energy is required for an active life • Excess energy is stored as glycogen or fat Table 21.14

  44. 21.15 Connection: Body fat and fad diets • The human body tends to store excess fat molecules instead of using them for fuel • A balanced diet includes adequate amounts of all nutrients

  45. Fad diets are often ineffective and can be harmful Table 21.15

  46. 21.16 Connection: Vegetarians must be sure to obtain all eight essential amino acids • The eight essential amino acids that adults require must be obtained from food • They are easily obtained from animal protein • They can also be obtained from the proper combination of plant foods ESSENTIALAMINO ACIDS Methionine Valine (Histidine) Threonine Phenylalanine Corn Leucine Isoleucine Beans andotherlegumes Tryptophan Lysine Figure 21.16

  47. 21.17 Connection: A healthful diet includes 13 vitamins • Most of these vitamins function as coenzymes

  48. Table 21.17 (Water-soluble vitamins)

  49. Table 21.17 (Fat-soluble vitamins)

  50. 21.18 Connection: Essential minerals are required for many body functions • Minerals are elements other than carbon, hydrogen, oxygen, and nitrogen • They play a variety of roles in the body