Animal Nutrition: Essentials and Homeostasis

1. Chapter 41: Animal Nutrition

2. The Need to Feed • Every mealtime is a reminder that we are heterotrophs Figure 41.1

3. 3 dietary categories • Herbivores eat mainly autotrophs (plants and algae) • Carnivores eat other animals • Omnivores consume animals as well as plants or algal matter

4. An adequate diet must satisfy 3 nutritional needs • Fuel for all cellular work • The organic raw materials for biosynthesis • Essential nutrients, substances such as vitamins that the animal cannot make for itself

5. Feces SUSPENSION FEEDERS SUBSTRATE FEEDERS Caterpillar Baleen FLUID FEEDERS BULK FEEDERS • Animals feed by four main mechanisms Figure 41.2

6. Homeostatic mechanisms manage animal’s energy budget • Animal’s ATP generation • Based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats

7. Glucose Regulation as an Example of Homeostasis • Animals store excess calories • As glycogen in the liver and muscles and as fat

8. When blood glucose level rises, a gland called the pancreas secretes insulin, a hormone, into the blood. 1 Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops. 2 Glucagon promotesthe breakdown ofglycogen in theliver and the release of glucose into the blood, increasing bloodglucose level. 4 When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin. 3 • Glucose  major fuel for cells • Its metabolism, regulated by hormone action, is an important example of homeostasis STIMULUS: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood STIMULUS: Blood glucose level drops below set point. Figure 41.3

9. When fewer calories are taken in than are expended • Fuel is taken out of storage and oxidized

10. Caloric Imbalance • Undernourishment • Occurs in animals when their diets are chronically deficient in calories • Detrimental effect on an animal

11. 100 µm • Overnourishment • Results from excessive food intake • Leads to the storage of excess calories as fat Figure 41.4

12. Obesity as a Human Health Problem • Major global health problem • Contributes to diabetes, cardiovascular disease, and colon and breast cancer

13. Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet. Produced by adipose (fat) tissue, leptin suppresses appetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases. Ghrelin Insulin Leptin The hormone PYY,secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin. A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin (see Figure 41.3). In addition to its other functions, insulin suppresses appetite by acting on the brain. PYY • Hormones regulate both long-term and short-term appetite (controlled by the brain) Figure 41.5

14. Mice that inherit a defect in the gene for leptin • Become very obese Figure 41.6

15. Obesity and Evolution • In the evolutionary past fat hoarding was a means of survival

16. Petrels • Become obese as chicks due to the need to consume more calories than they burn Figure 41.7

17. Animal’s diet must supply carbon skeletons and essential nutrients

18. Herbivorous animals • May suffer mineral deficiencies if they graze on plants in soil lacking key minerals Figure 41.8

19. Essential Amino Acids • Animals require 20 amino acids • Synthesize about half of them from the other molecules they obtain from their diet • Essential amino acids • Must be obtained from food in preassembled form

20. A diet that provides insufficient amounts of one or more essential amino acids causes protein deficiency Figure 41.9

21. Essential amino acids for adults Beansand other legumes Methionine Valine Threonine Phenylalanine Leucine Corn (maize)and other grains Isoleucine Tryptophan Lysine Figure 41.10 • Most plant proteins are incomplete in amino acid makeup •  eat a variety to get all the essential amino acids

22. Vitamins • Vitamins are organic molecules • Required in the diet in small amounts • To date, 13 vitamins essential to humans • Have been identified

23. 2 categories • Fat-soluble and water-soluble Table 41.1

24. Minerals • Simple inorganic nutrients • Usually required in small amounts

25. Mineral requirements of humans Table 41.2

26. The main stages of food processing are ingestion, digestion, absorption, and elimination • Ingestion, the act of eating • 1st stage of food processing

27. Digestion • Process of breaking food down into molecules small enough to absorb • Involves enzymatic hydrolysis of polymers into their monomers

28. Absorption • Uptake of nutrients by body cells • Elimination • Undigested material passes out of the digestive compartment

29. ELIMINATION 4 ABSORPTION 2 DIGESTION 1 3 • The four stages of food processing Smallmolecules Piecesof food Chemical digestion(enzymatic hydrolysis) Nutrient moleculesenter body cells Mechanicaldigestion Undigested material Food INGESTION Figure 41.12

30. Intracellular Digestion • Food particles are engulfed by endocytosis and digested within food vacuoles

31. Extracellular Digestion • Breakdown of food particles outside cells

32. Tentacles Mouth Food Gastrovascularcavity Epidermis Mesenchyme Gastrodermis Nutritivemuscularcells Flagella Gland cells Food vacuoles Mesenchyme • Animals with simple body plans • Have a gastrovascular cavity, functions in both digestion and distribution of nutrients Figure 41.13

33. Complex animals • Digestive tube with two openings, a mouth and an anus • Called a complete digestive tract or an alimentary canal

34. Anus Anus Gastric ceca Crop • Specialized regions • Digestion and nutrient absorption in a stepwise fashion Esophagus Crop Gizzard Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption. Intestine Pharynx Mouth Typhlosole Lumen of intestine Midgut Hindgut Foregut (b) Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients. Esophagus Rectum Mouth Crop Esophagus (c) Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine. Gizzard Mouth Intestine Figure 41.14a–c Stomach Anus

35. Mammalian digestive system alimentary canal and accessory glands

36. Salivaryglands Cardiacorifice Tongue Oral cavity Mouth Salivaryglands Pharynx Parotid gland Sublingual gland Esophagus Esophagus Submandibular gland Pyloricsphincter Liver Gall-bladder Stomach Stomach Gall-bladder Ascendingportion of large intestine Small intestines Liver Pancreas Pancreas IIeumof small intestine Large intestines Small intestine Duodenum of small intestine Rectum Anus Large intestine Rectum A schematic diagram of the human digestive system Appendix Anus Cecum Figure 41.15

37. Food is pushed along the digestive tract by peristalsis • Rhythmic waves of contraction of smooth muscles in the wall of the canal

38. The Oral Cavity, Pharynx, and Esophagus • Digestion begins • And teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of glucose polymers

39. Throat (pharynx) • Junction that opens to both the esophagus and the windpipe (trachea) • Esophagus • Food  stomach by peristalsis

40. The esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Epiglottisup Bolus of food Tongue Glottisdown and open Epiglottisup Esophageal sphincterrelaxed Pharynx Epiglottis down Esophageal sphinctercontracted Esophageal sphinctercontracted Glottis After the food has entered the esophagus, the larynx moves downward and opens the breathing passage. Larynx Esophagus Trachea To lungs To stomach Glottis upand closed Contractedmuscles Relaxedmuscles Relaxedmuscles The larynx, the upper part of the respiratory tract, moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea. 2 1 6 5 3 4 Waves of muscular contraction (peristalsis) move the bolus down the esophagus to the stomach. When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs. The swallowing reflex is triggered when a bolus of food reaches the pharynx. Figure 41.16 Stomach • From mouth to stomach

41. The Stomach • Secretes gastric juice, which converts a meal to acid chyme • Gastric juice • Hydrochloric acid and the enzyme pepsin

42. Stomach Esophagus Cardiac orifice Folds of epithelial tissue Pyloric sphincter 5 µm Small intestine 2 3 1 1 3 2 Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands. Pepsinogen and HCI are secreted into the lumen of the stomach. Epithelium HCl converts pepsinogen to pepsin. Pepsinogen Pepsin (active enzyme) Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells. HCl Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. Chief cells secrete pepsino- gen, an inactive form of the digestive enzyme pepsin. Parietal cell Chief cell Parietal cells secrete hydrochloric acid (HCl). • The lining of the stomach • Is coated with mucus, which prevents the gastric juice from destroying the cells

43. Bacteria Mucuslayer of stomach 1 µm • Gastric ulcers, lesions in the lining • Are caused mainly by the bacterium Helicobacter pylori Figure 41.18

44. The Small Intestine • Longest section of the alimentary canal • Major organ of digestion and absorption

45. Liver Stomach Bile Gall-bladder Acid chyme Intestinaljuice Pancreas Pancreatic juice Duodenum of small intestine Enzymatic Action in the Small Intestine • First portion of the small intestine (duodenum) • Acid chyme from stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself Figure 41.19

46. Pancreas Membrane-boundenteropeptidase Inactivetrypsinogen Trypsin Other inactiveproteases Active proteases Lumen of duodenum • The pancreas produces proteases, protein-digesting enzymes • That are activated once they enter the duodenum Figure 41.20

47. Protein digestion Fat digestion Nucleic acid digestion Carbohydrate digestion Polysaccharides (starch, glycogen) Oral cavity, pharynx, esophagus Disaccharides (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Polypeptides Polysaccharides DNA, RNA Lumen of small intes- tine Fat globules (Insoluble in water, fats aggregate as globules.) Pancreatic amylases Pancreatic nucleases Pancreatic trypsin and chymotrypsin (These proteases cleave bonds adjacent to certain amino acids.) Bile salts Maltose and other disaccharides Fat droplets (A coating of bile salts prevents small drop- lets from coalescing into larger globules, increasing exposure to lipase.) Nucleotides Smaller polypeptides Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Small peptides Nucleotidases Epithelium of small intestine (brush border) Nucleosides Disaccharidases Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.) Nucleosidases and phosphatases Monosaccharides Nitrogenous bases, sugars, phosphates Amino acids Enzymatic digestion Figure 41.21

48. Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum. Liver Entero- gastrone Gall- bladder Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices. Gastrin CCK Stomach Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. Pancreas Secretin Duodenum Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach. CCK Key Stimulation Inhibition • Hormones coordinate the secretion of digestive juices into the alimentary canal Figure 41.22

49. Microvilli(brush border) Vein carrying blood to hepatic portal vessel Bloodcapillaries Muscle layers Epithelialcells Epithelial cells Largecircularfolds Lacteal Villi Key Lymph vessel Villi Nutrientabsorption Intestinal wall • The enormous microvillar surface area • Greatly increases the rate of nutrient absorption Figure 41.23

50. Amino acids and sugars • Pass through the epithelium of the small intestine and enter the bloodstream