Chapter 41

1. Chapter 41 Animal Nutrition

2. Overview: The Need to Feed • Every meal reminds us that we are heterotrophs, dependent on a regular supply of food • In general, animals fall into three categories: • Herbivores eat mainly autotrophs (plants and algae) • Carnivores eat other animals • Omnivores regularly consume animals as well as plants or algal matter

4. An adequate diet must satisfy three needs: • Fuel for all cellular work • Organic raw materials for biosynthesis • Essential nutrients, substances that the animal cannot make for itself • Main feeding mechanisms: suspension feeding, substrate feeding, fluid feeding, bulk feeding

5. LE 41-2a Baleen

6. LE 41-2b Caterpillar Feces

7. Video: Lobster Mouth Parts Video: Shark Eating a Seal

8. Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget • Nearly all of an animal’s ATP generation is based on oxidation of energy-rich molecules: carbohydrates, proteins, and fats

9. Glucose Regulation as an Example of Homeostasis • Animals store excess calories as glycogen in the liver and muscles and as fat • Glucose is a major fuel for cells • Hormones regulate glucose metabolism • When fewer calories are taken in than are expended, fuel is taken from storage and oxidized

10. LE 41-3 STIMULUS: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood STIMULUS: Blood glucose level drops below set point.

11. Caloric Imbalance • Undernourishment occurs in animals when their diets are chronically deficient in calories • Overnourishment, or obesity, results from excessive intake, with excess stored as fat

12. LE 41-4 100 µm

13. Obesity as a Human Health Problem • The World Health Organization now recognizes obesity as a major global health problem • Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer

14. Researchers have discovered several of the mechanisms that help regulate body weight • Over the long term, homeostatic mechanisms are feedback circuits that control the body’s storage and metabolism of fat • Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain

15. LE 41-5 Ghrelin Insulin Leptin PYY

16. The complexity of weight control in humans is evident from studies of the hormone leptin • Mice that inherit a defect in the gene for leptin become very obese

18. Obesity and Evolution • The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival • A species of birds called petrels become obese as chicks due to the need to consume more calories than they burn

20. Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients • An animal must obtain carbon skeletons from its food to build complex molecules • Besides fuel and carbon skeletons, a diet must supply essential nutrients in preassembled form • A malnourished animal is missing one or more essential nutrients in its diet

21. Herbivores may suffer mineral deficiencies if they graze on plants in soil lacking key minerals

23. Malnutrition is much more common than undernutrition in human populations

24. Essential Amino Acids • Animals require 20 amino acids and can synthesize about half from molecules in their diet • The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form • A diet that provides insufficient essential amino acids causes malnutrition called protein deficiency

26. Most plant proteins are incomplete in amino acid makeup • Individuals who eat only plant proteins need to eat a variety to get all essential amino acids

27. LE 41-10 Essential amino acids for adults Beans and other legumes Methionine Valine Threonine Phenylalanine Leucine Corn (maize) and other grains Isoleucine Tryptophan Lysine

28. Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein

30. Essential Fatty Acids • Animals can synthesize most of the fatty acids they need • The essential fatty acids are certain unsaturated fatty acids • Deficiencies in fatty acids are rare

31. Vitamins • Vitamins are organic molecules required in the diet in small amounts • 13 vitamins essential to humans have been identified • Vitamins are grouped into two categories: fat-soluble and water-soluble

34. Minerals • Minerals are simple inorganic nutrients, usually required in small amounts

36. Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination • Ingestion is the act of eating • Digestion is the process of breaking food down into molecules small enough to absorb • Absorption is uptake of nutrients by body cells • Elimination is the passage of undigested material out of the digestive compartment

37. LE 41-12 Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Undigested material Food INGESTION ELIMINATION DIGESTION ABSORPTION

38. Digestive Compartments • Most animals process food in specialized compartments • These compartments reduce risk of self-digestion

39. Intracellular Digestion • In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles

40. Extracellular Digestion • Extracellular digestion is the breakdown of food particles outside of cells • It occurs in compartments that are continuous with the outside of the animal’s body

41. Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Video: Hydra Eating Daphnia

42. LE 41-13 Mouth Tentacles Gastrovascular cavity Food Epidermis Mesoglea Gastrodermis Nutritive muscular cells Flagella Gland cells Food vacuoles Mesoglea

43. More complex animals have a digestive tube with two openings, a mouth and an anus • This digestive tube is called a complete digestive tract or an alimentary canal • It can have specialized regions that carry out digestion and absorption in a stepwise fashion

44. LE 41-14a Crop Gizzard Intestine Esophagus Pharynx Anus Mouth Typhlosole Lumen of intestine Earthworm

45. LE 41-14b Midgut Hindgut Foregut Esophagus Rectum Anus Crop Mouth Gastric ceca Grasshopper

46. LE 41-14c Esophagus Stomach Gizzard Intestine Mouth Crop Anus Bird

47. Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions • The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts • Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder • Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

48. LE 41-15a Cardiac orifice Tongue Oral cavity Parotid gland Salivary glands Sublingual gland Pharynx Esophagus Submandibular gland Pyloric sphincter Liver Stomach Ascending portion of large intestine Gall- bladder Pancreas Duodenum of small intestine Ileum of small intestine Small intestine Large intestine Rectum Anus Appendix Cecum

49. LE 41-15b Salivary glands Mouth Esophagus Gall- bladder Stomach Small intestines Liver Pancreas Large intestines Rectum Anus A schematic diagram of the human digestive system

50. The Oral Cavity, Pharynx, and Esophagus • In the oral cavity, food is lubricated and digestion begins • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers