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

3. 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. 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

8. 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.

9. LE 41-4 100 µm

10. 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

12. LE 41-5 Ghrelin Insulin Leptin PYY

13. 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

14. Obesity and Evolution • The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival

15. 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 • A malnourished animal is missing one or more essential nutrients in its diet

16. Essential Amino Acids • Animals require 20 amino acids and can synthesize about half from molecules in their diet • Essential amino acids, must be obtained from food in preassembled form • Malnutrition called protein deficiency occurs when a diet doesn’t contain all needed amino acids

17. Kwashiorkor Caused by a protein deficiency

18. 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

20. 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

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

25. Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination • Ingestion • Digestion • Absorption • Elimination

26. 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

27. Mouth Tentacles Gastrovascular cavity Food • Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Epidermis Mesoglea Gastrodermis Nutritive muscular cells Flagella Gland cells Food vacuoles Mesoglea Video: Hydra Eating Daphnia

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

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

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

31. 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

32. 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

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

34. 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

35. LE 41-16_3 Bolus of food Tongue Epiglottis up Epiglottis up Pharynx Glottis down and open Esophageal sphincter contracted Glottis Esophageal sphincter relaxed Epiglottis down Esophageal sphincter contracted Larynx Glottis up and closed Trachea Esophagus Relaxed muscles To stomach To lungs Contracted muscles Relaxed muscles Stomach

36. The Stomach • The stomach stores food and secretes gastric juice, which converts a meal to acid chyme • Gastric juice is made up of hydrochloric acid and the enzyme pepsin • Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach • Mucus protects the stomach lining from gastric juice

37. HCl Pepsinogen Pepsin

38. LE 41-17 Esophagus Cardiac orifice Stomach Pyloric sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Epithelium Pepsinogen and HCl are secreted into the lumen of the stomach. Pepsinogen Pepsin (active enzyme) Gastric gland HCl HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Mucus cells Chief cells Parietal cells Chief cell Parietal cell

39. Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori Bacteria Mucus layer of stomach 1 µm

40. The Small Intestine • The small intestine is the longest section of the alimentary canal • It is the major organ of digestion and absorption

41. LE 41-19 Bile Liver Gall- bladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine

42. The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum

43. LE 41-20 Pancreas Membrane-bound enteropeptidase Inactive trypsinogen Trypsin Other inactive proteases Active proteases Lumen of duodenum

44. The liver produces bile, which aids in digestion and absorption of fats • The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes

45. LE 41-21 Protein digestion Nucleic acid digestion Fat digestion Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides Salivary amylase Smaller polysac- charides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intes- tine DNA, RNA Fat globules Polysaccharides Polypeptides Pancreatic amylases Pancreatic nucleases Pancreatic trypsin and chymotrypsin Bile salts Maltose and other disaccharides Fat droplets Nucleotides Smaller polypeptides Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Epithelium of small intestine (brush border) Small peptides Nucleotidases Nucleosides Dipeptidases, carboxy- peptidase, and aminopeptidase Disaccharidases Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Amino acids Monosaccharides

46. LE 41-22 Key Liver Stimulation Inhibition Entero- gastrone Gall- bladder Gastrin CCK Stomach Pancreas Secretin Duodenum CCK

47. Absorption of Nutrients • The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen • The enormous microvillar surface greatly increases the rate of nutrient absorption

48. LE 41-23 Key Nutrient absorption Vein carrying blood to hepatic portal vessel Microvilli (brush border) Blood capillaries Epithelial cells Muscle layers Epithelial cells Large circular folds Lacteal Villi Lymph vessel Villi Intestinal wall

49. Fat globule • Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream • After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells Bile salts Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelium of small intestine Lacteal Epithelium of lacteal

50. The Large Intestine • The large intestine, or colon, is connected to the small intestine • Its major function is to recover water that has entered the alimentary canal