Digestive Systems

1. Digestive Systems • Campbell, 6th edition, Chapter 41 • Animal Nutrition

2. DIGESTIVE SYSTEMS I. Digestion • Food Types • Feeding Mechanisms IV. Compartmentalization V. Stages of Food Processing VI. Types of Digestive Systems VII.Vertebrate Digestive System & Regulation

3. I. Digestion • 1) fuel (chemical energy) • 2) raw organic materials (biosynthesis) • 3) essential nutrients • Homeostatic mechanisms manage these resources. • Know difference between undernourished and malnourished. Any nutritionally adequate diet satisfies three needs:

4. Essential Nutrients • 8 Amino Acids: tyrptophanmethionine valine threonine phenylalanineleucine isoleucinelysine (histidine is essential for infants) • Fatty acids: membrane structure unsaturated; linoleic acid • 13 Vitamins: coenzymes Fat-soluble: vitamins A, D, E, & K Water-soluble: B complex,Vitamin C • Minerals: building materials, cofactors Ca, P, S, K, Cl, Fe, Mg, Zn, I, Na,

5. Essential amino acids from a vegetarian diet.

9. I. Digestion • Chemical and mechanical breakdown of organic molecules into units small enough for the body to absorb. • These molecules provide: • 1) Energy resources • 2) Essential chemical elements • 3) Raw materials for anabolism

10. Food Types • Most animals are opportunistic feeders: 1) HERVIVORES – feed on autotrophs 2) CARNIVORES – eat other animals 3) OMNIVORES – both

11. III. Feeding Mechanisms Four major groups: • suspension-feeders Baleen whale, clam, oyster • substrate-feeders Leaf miner, earthworm • fluid-feeders Mosquito, leech • bulk-feeders Python, lion, bear

12. Suspension-feeding: a baleen whale

13. Substrate-feeding: leaf miner

14. Fluid-feeding: a mosquito

15. Bulk-feeding: a python

16. IV. Digestion is compartmentalized • Intracellular – digestive enzymes are secreted by cells & food is digested by enzymes within the cell • sponges (choanocytes) • Extracellular - digestive enzymes are secreted by cells into a digestive cavity • cnidarians (both intracellular & extracellular)

17. Intracellular digestion in Paramecium

18. Extracellular digestion in a gastrovascular cavity.

19. V. Stages of Food Processing • Ingestion • the act of eating or ingesting • Digestion • process of breaking food into small enough molecules for the body to absorb • Absorption • process of absorbing small molecules from the digestive compartment into bloodstream • Egestion • act of eliminating undigested materials from the digestive compartment

20. VI. Types of Digestive Systems • Channel network • Porifera • Incomplete (one-hole sac or gastrovascular cavity) • Cnidarians  Platyhelminthes • Complete (two-hole sac or alimentary canal) • Nematoda  Chordata

21. VI. Types of Digestive Systems • Incomplete Digestive Tract or gastrovascular cavity • functions in digestion (gastro) & distribution (vascular) • dual role: mouth = anus • Cnidaria Platyhelminthes

22. VI. Types of Digestive Systems • Complete Digestive Tract • Alimentary canal • food moves in one direction • tube is organized into specialized regions • Nematoda  Chordata

23. Alimentary Canal

24. Complete digestive tract of a mollusk

25. Earthworm Digestive Tract

26. The Human Digestive System

27. VII. Vertebrate Digestive System Oral cavity: mouth, tongue, teeth • digestion begins here • mastication= mechanical grinding action of teeth • food soften with saliva from salivary glands • bolus = moistened ball of food

28. Accessory Organs: Salivary Glands Saliva • contains mucus for lubrication and swallowing (1 - 1.5 L per day) • contains salivary amylase- hydrolysis of amylose • contains mucin, buffers, antibacterial agents • venom- secreted by the salivary glands of some vertebrates • Parotid, submaxillary, sublingual salivary glands

29. Pharynx (throat region) • swallowing is accomplished by the pharynx • an intersection leads to both esophagus and trachea; cartilage flap, epiglottis, covers the glottis & prevents choking (Figure 41.12) • passes bolus from mouth to esophagus • originates from a groove in the floor of the lungs • acts as a muscular pump in some worms (proboscis w/ pharynx)

30. From mouth to stomach: the swalling reflex and esophageal peristalsis

31. Esophagus • 25 cm long • muscularized passageway to stomach • peristalsis begins here rhythmic waves of contraction by smooth muscles in the wall of the canal • ruminants (cud-chewers), ruminating pouches, chambers of esophagus where fermentation occurs (cows produce 60 L saliva per day & burp 2 L gas/minute)

32. Layers of the Digestive Tube From esophagus to anus: • 1) mucosa – lines tube; glandular epithelium; villi; contains some smooth muscle; produces mucus • 2) submucosa – connective tissue, nerves, blood vessels, lymph • 3) muscularis externa – inner circular muscle & outer longitudinal muscle • 4) serosa – outer fibrous coating or visceral peritoneum

33. Cardiac sphincter • ringlike valve of smooth muscle that functions like a drawstring • controls entrance of food into stomach from esophagus

34. Stomach • collapsible muscular bag • suspended in abdominal cavity by folds of peritoneum called mesentery • functions in mechanical mixing of food with HCl and enzymes • fully distended, human stomach holds 2-4 liters of food

35. 3 regions of the Stomach: • 1) cardiac – upper • 2) fundus – deep, storage • 3) pylorus – lower, empties into small intestine

36. Stomach • glucose and alcohol are absorbed in stomach • takes about 4 hours to empty stomach • chyme – semi-liquid mass; may back up in gastric pits and cause ulcers

37. Stomach • Rugae – folds of stomach with deep pockets, or gastric pits, contain • 1) mucous cells – secrete mucus for protection • 2) parietal cells – secrete HCl (pH 1.5-2.5) HCL kills most bacteria & living cells; erodes plant materials; initiates change of pepsinogen to pepsin • 3) chief cells – secrete pepsinogen (inactive) which is converted by HCL into active pepsin

38. Chemical Digestion

39. Digestion in Stomach Digestion is regulated by hormones and the Autonomic Nervous System • Stomach hormone: Gastrin • produced in the presence of protein-containing food in the stomach • stimulates the release of gastric juices and muscular contractions of stomach & intestine • Blood sugar is regulated by pancreatic hormones insulin and glucagon

40. Accessory Digestive Organs

41. Ruminant digestion

42. Enzymatic Digestion in the human digestive system

43. Digestion in Stomach Stimulation of epithelial cells of stomach mucosa increases secretion of gastric juice: • 1) mucous • 2) HCl • 3) pepsinogen • 4) renin(hydrolyzes milk) • 5) water

44. Pyloric sphincter • sphincter separating the stomach and small intestine • regulates the passage of material from stomach to small intestine

45. Small Intestine • digestion is completed here • most enzymatic hydrolysis and adsorption occurs here • surface area of small intestine is 300 m2;about the size of a double tennis court • mucosa has fingerlike projections, villi, which extend into the lumen • the villi have microvilli (cytoplasmic projections on the surface of epithelial cells) Figure 41.15

46. Structure of the small intestine

47. Small Intestine • Small intestine is 20-23’ long: • 1) duodenum 8-10” • 2) jejunum 8’ • 3) ileum 12’ • duodenum – most active in digestion • jejunum & ileum – absorption • study Figure 41.13: Enzymatic digestion

48. Digestion in Small Intestine Digestion is regulated by hormones and the Autonomic Nervous System • Duodenal hormones: • 1) secretin – stimulates pancreas & liver to secrete alkaline fluids • 2) cholecystokinin – triggers release of enzymes from pancreas and gall bladder (amylase, lipase, deoxyribonuclease, protease, etc.)

49. Activation of protein-digesting enzymes in the small intestine

50. Accessory Organs: Liver • largest internal organ = 3 lb chemical factory • processes food by the Hepatic Portal Vein delivered from digestive tract • variable nutrient levels in HPV while level in systemic circulation remains constant • though the liver performs many functions, cells of the liver function without division of labor