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Chapter 41

Chapter 41. Animal Nutrition. Modern humans foraging at a farmer’s market. Four Main Feeding Mechanisms of Animals. SUSPENSION FEEDERS. SUBSTRATE FEEDERS. Feces. Baleen. Caterpillar. FLUID FEEDERS. BULK FEEDERS. Homeostatic regulation of cellular fuel.

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Chapter 41

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  1. Chapter 41 Animal Nutrition

  2. Modern humans foraging at a farmer’s market

  3. Four Main Feeding Mechanisms of Animals SUSPENSION FEEDERS SUBSTRATE FEEDERS Feces Baleen Caterpillar FLUID FEEDERS BULK FEEDERS

  4. Homeostatic regulation of cellular fuel

  5. 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. In addition to its other functions, insulin suppresses appetite by acting on the brain. PYY A few of the appetite-regulating hormones

  6. A ravenous rodent

  7. Essential amino acids from a vegetarian diet

  8. Vitamin Requirements of Humans: Water-Soluble Vitamins

  9. Vitamin Requirements of Humans: Fat-Soluble Vitamins

  10. Mineral Requirements of Humans

  11. Obtaining essential nutrients

  12. Kwashiorkor (a protein deficiency) in a Haitian boy

  13. Intracellular digestion in Paramecium

  14. Extracellular digestion in a gastrovascular cavity

  15. Anus Anus Gastric ceca Crop Variation in alimentary canals Crop 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. Gizzard Esophagus Intestine Pharynx Mouth Typhlosole Lumen of intestine Foregut Midgut Hindgut (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 Gizzard (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. Mouth Intestine Stomach Anus

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

  17. Small intestine Stomach Small intestine Cecum Colon(large intestine) The digestive tracts of a carnivore (coyote) and herbivore (koala) compared Carnivore Herbivore

  18. Rumen. When the cow first chews and swallows a mouthful of grass, boluses (green arrows) enter the rumen. Intestine 1 2 3 4 Esophagus Abomasum. The cud, containing great numbers of microorganisms, finally passes to the abomasum for digestion by the cow‘s own enzymes (black arrows). Ruminant digestion Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of their metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down the fibers, making them more accessible to further microbial action. Omasum. The cow then reswallows the cud (blue arrows), which moves to the omasum, where water is removed.

  19. The human digestive system

  20. From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 1)

  21. From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 2)

  22. From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 3)

  23. The duodenum

  24. Enzymatic digestion in the human digestive system

  25. The structure of the small intestine

  26. Large intestine

  27. Digital image of a human colon

  28. Dentition and diet

  29. Bacteria Mucuslayer of stomach 1 µm Ulcer-causing bacteria

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