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Chapter 41

Chapter 41. Digestion. Digestive Systems. Absorb nutrients necessary to maintain life, eliminate wastes Ingestion Digestion Absorption Elimination Digestion —process by which food is chemically and mechanically broken down for use by the body. Digestive Systems. No digestive system

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Chapter 41

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  1. Chapter 41 Digestion

  2. Digestive Systems • Absorb nutrients necessary to maintain life, eliminate wastes • Ingestion • Digestion • Absorption • Elimination • Digestion—process by which food is chemically and mechanically broken down for use by the body

  3. Digestive Systems • No digestive system • Sponges, tapeworms • Absorb only small molecules • Digestion intracellular

  4. Digestive Systems • Incomplete • Cnidarians, planarians • Single body opening (Gastrovascular cavity) • Limited enzymes • Digestion begins extracellularly • Digestion completed intracellularly • No regions w/ specialized function

  5. Digestive Systems • Complete • Annelids, mollusks, arthropods, vertebrates, etc. (most animals) • Two openings (mouth & anus) • Different regions w/ specialized function • Digestion primarily extracellular

  6. Digestive Systems • Continuous feeders • Filter feeders (clams, mussels, barnacles, etc.) • Must complete digestion quickly • Discontinuous feeders • Most animals • Feed periodically • Need storage area in gut

  7. Complete Digestive System • Functions • Mechanical processing & motility • Secretion of digestive enzymes • Chemical digestion • Absorption • Elimination of wastes • Anatomy determined by lifestyle • Carnivore • Herbivore • Omnivore

  8. Mouth • Initial digestion begins • Mechanical break-down of food • No teeth • Worms, birds—swallow food whole • Grinding done lower in digestive tract • Insects—some chew, some suck • Arachnids—no chewing • Suck existing fluids • Inject digestive fluids into prey

  9. Mouth • Teeth • Vertebrates only • Incisors—shearing • Canines—puncture, tearing • Capture prey • Fighting predators or within species • Premolars—grinding • Molars—crushing

  10. Mouth • Herbivores • Plant material tough • Emphasis on grinding, crushing • Broad, flat premolars & molars • Limited or absent canines

  11. Mouth • Carnivores • Animal material easier to mechanically tear • Emphasis on piercing, cutting • Long, pointed canines • Molars & premolars modified for shearing or piercing

  12. Mouth • Omnivores • Combination teeth • Varies based on amount of each type of food

  13. Mouth • Salivary glands • Secrete via ducts into mouth • Lubricate & moisten food • Salivary amylase • Begins to digest starches • Tongue • Grab food • Manipulate food • Taste

  14. Esophagus • Muscular tube • Lined by stratified squamous epithelium • Moves food from mouth to next step • Peristalsis—rhythmic contractions of gastrointestinal tract

  15. Upper GI • Crop • Insects • Annelids • Most birds • Temporary storage

  16. Upper GI • Proventriculus • Birds, many invertebrates • Secretes digestive enzymes • Gizzard • Birds, many invertebrates, some reptiles • Dinosaurs • Thick, muscular walls • Grinding food • Chitinous plates in some insects & mollusks • Birds swallow “grit” to use for grinding

  17. Upper GI • Stomach (monogastric) • Temporary storage • Mechanical churning • Digestive enzymes • Combined functions of crop, proventriculus, gizzard • Pepsin—breaks down proteins • Hydrochloric acid—slows salivary amylase, activates pepsin

  18. Upper GI • Stomach (ruminant) • Cattle, goats, llamas, camels, deer, sheep, etc. • Four-chambered stomach • Rumen, reticulum, omasum, abomasum • Food swallowed, separated in reticulorumen • Solid (cud) regurgitated from reticulum • Cud chewed for further breakdown, then swallowed • Moved to omasum, water & inorganic minerals absorbed • Moves to abomasum, like monogastric stomach

  19. Lower GI • Small intestine • Short in carnivores • Long in herbivores • Duodenum • Jejunum • Ileum

  20. Lower GI • Secretion of enzymes • Intestinal mucosa • Gall bladder • Pancreas • Absorption • Villi—folds of intestinal lining • Microvilli—folds of intestinal cells

  21. Lower GI • Cecum • Single in mammals • Double in most birds & some reptiles • Large in herbivores • Reduced in carnivores • Remove fluids & salts • In herbivores has large numbers of bacteria to break down plant material

  22. Lower GI • Colon (large intestine) • Most food digested & absorbed by this point • Water & waste • Functions to reabsorb water • Diarrhea—water not absorbed properly • Rectum • Storage of feces ready for elimination • Anus • Muscular sphincter controlling elimination of feces

  23. Other Organs • Liver • Secretes bile (breaks down fats) • Many other important functions • Gall bladder • Stores & concentrates bile • Not present in all animals, even if closely related • Absent horse, deer; present cow, goat, sheep • Absent doves; present hawks & owls • Absent rats; present mice • Pancreas • Many enzymes to break down food • Buffers against HCl from stomach

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