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CHAPTER 4

CHAPTER 4. The Gastrointestinal Tract and Nutrition. Introduction.

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CHAPTER 4

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  1. CHAPTER 4 The Gastrointestinal Tract and Nutrition

  2. Introduction • Many of the organic components of food are in the form of large insoluble molecules which have to be broken down into simple compounds before they can pass through the mucous membrane of the alimentary cannel into the blood and lymph. The breaking down process is termed digestion, the passage of the digested nutrients through the mucous membrane absorption.

  3. Digestion in monogastric mammals • GI tract = gastrointestinal tract • Digestion: mechanical forces • chemical action • hydrolysis of ingesta • Absorption: • small molecules from lumen → • mucosal surface → • blood, lymph • monogastric (nonruminant) , ruminant.

  4. Carnivores: • relatively short and uncomplicated intestine: dog, mink. • Omnivores: • long small intestine, moderately caecum and a sacculated large intestine.

  5. Coprophagy (feces eating) : • rabbit • soft feces, hard feces • supply of vitamins and amino acid

  6. GI tract of nonruminant • Stomach: • 1. oesophagus region: • no gland, α-amylase activity continue, active microbial population (mainly Lactobacillus, Streptococci) • 2. cardia region: • produce gel- forming glycoprotein(mucus), protecting the stomach,

  7. 3.fundus gland region: • peptic cells produce proteolytic enzyme, parietal cell secrete HCl • 4.pyloric region: • like those in the cardia region.

  8. Gastric juice • water, • pepsinogen, • inorganic salts • mucus • HCl • intrinsic factor.

  9. Four pepsins have been found in the pig which have optimum pH with 2.0 and 3.5. Pepsin preferentially attack those peptide bonds of aromatic amino acids, (phenylalanine, tryptophan, and tyrosine). Rennin or chymosin are also occur in the gastric juice.

  10. Small intestine and digestion 1. duodenum: • covered with finger like, or plate or tongue like villi, brush border enzyme. • The duodenum is the site for mixing digesta and secretion and the jejunum being the site of absorption. • 2. jejunum • 3. ileum

  11. Bile is secreted by the liver and passes to the duodenum through the bile duct. It contains the sodium and potassium salts of bile acids, chiefly glycocholic and taurocholic, phospholipids and bile pigments.

  12. The bile salts play an important part in digestion by activating lipase and emulsifying fats. • Pancreas is a gland which lies in the duodenal loop and two secretory functions. ( Insulin and digestive enzymes)

  13. Secretion stimulate route: • Acid enter the duodenum→ • secretin is liberated from the epithelium of the small intestine into blood → • when it reach the pancreatic circulation, stimulates the pancreatic cells to secrete a water fluid containing bicarbonate ions and little enzyme.

  14. Cholecystokinin(CCK) is liberated from the mucosa when peptides and other digestive products reach the duodenum.→ • CCK stimulates the secretion of proenzyme into pancreas juice.

  15. pancreas juice • proenzyme such as trypsinogen chymotrypsinogen • Procarboxypeptidases A and B • proelastase, • α-amylase • lipase • lecithinases • nucleases

  16. The inactive zymogen is converted to the active enzyme by enterokinase, an enzyme liberated from the duodenal mucosa.

  17. Digestion in the small intestine include • lumen digestion. • membrane digestion.

  18. The hydrolysis of oligosaccharides to monosaccharides and of small peptide to amino acids is brought about by enzyme associated with the intestinal villi. (called brush border enzymes)

  19. Enzymes produced are sucrase, maltase, lactase , oligo-1,6-glucosidases, and aminopeptidase.

  20. Large intestine and digestion • Absorption of water • secretion of inorganic element • Extensive bacterial fermentation , Slow rate of passage and abundant nutrient sources encourage the prolific growth of bacteria. • Cecum, colon,rectum

  21. Bacteria: • Indole, skatole • phenol, H2S • amines, NH3, • volatile fatty acids(VFA , include acetic acid, propionic acid, butyric acid), • H2, B vitamins.

  22. GI tract of avian (fowl) • crop: fermentation (lactobacillus) • proventriculus: gastric juices • gizzard: • small intestine: enzyme • Cecum(ceca): bacterial fermentation • colonic – recturm • The digestive enzyme secretion are similar to those of mammals. But lactase not been detected.

  23. Absorption of digested nutrients • The duodenum has villi is primarily a mixing and neutralizing site and the jejunum is the major absorptive site.

  24. Role of the GI tract in transport of nutrients • The passage route of nutrients from the intestine lumen into the intestinal epithelial cell and then into the blood or lymph by active, passive transport.

  25. Passive transport : • passive diffusion(high concentration toa low concentration diffusion) • facilitative transport (carrier transport the molecule down its concentration gradient).

  26. Active transport: • the carrier has two specific binding sites and the nutrient is attached to one of these while other site picks up a sodium(in case of monosaccharides and amino acids) or a hydrogen ion (in case of dipeptides). • Sodium pump. • Na/K transporting ATPase.

  27. pinocytosis ( cell drinking), phagocytosis • pinocytosis occurs in new born animal to absorption of immunoglobulins, proteins , peptide from colostrum.

  28. *transport route • penetration of the microvillus • migration through the cell interior • possible metabolism within the cell • extrusion from lateral and basal of the cell • passage through the basement membrane • penetration through the epithelium into blood or lymph.

  29. Blood and Nutrition • Blood is the vehicle for transport of nutrients and metabolites among organs, tissues and cells of the body, Nutrients transport by carrier or binding protein.

  30. GI tract of ruminant 1. Saliva: • 150L (cow), 10L(sheep), eating and ruminating produced. • Provide a source of N (urea and mucoproteins). P, Na, Buffered • maintaining a pH in the rumen

  31. 2. Stomach (rumen, reticulum, omasum, and abomasum) . • Rumen: • high population of microorganism(1010 – 1012)fermentation.

  32. Reticulum: • moving food into rumen or into the omasum • Omasum: • reducing particle size, control passage of ingesta. • Abomasum: • glandular stomach

  33. The reticulo-rumen provides a continuous culture system for anaerobic bacteria, protozoa and fungi. • Food and water enter the rumen and the food is fermented to yield volatile fatty acids, microbial cells and gas methane and carbon dioxide.

  34. The acids produced by fermentation are capable of reducing the pH of rumen liquor to 2.5-3.0, but under normal condition the pH is maintained at 5.5-6.0.

  35. reticular groove ( esophageal groove) • Begins at the lower end of the esophagus and, when closed, forms a tube from the esophagus into the omasum. • Allow milk bypass the reticulorumen, and escape bacterial fermentation. • It is stimulated by the sucking, certain ions, solid in liquid

  36. rumination: • semi-liquid materials regurgitate up the esophagus, swallowed the liquid, and remastication of and swallowed the bolus. • 8h/day • inhibition of rumination result reduced in feed intake

  37. Eructation: • contraction of the upper sacs of the rumen which force the gas forward and allow the gas to escape.

  38. Rumen microorganisms • The bacteria number 109-1010 per mL of rumen contents.Over 200 species have been identified. • Typical rumen bacteria showed in Table 8.3

  39. Protozoa are present in small numbers (10 6 per mL), being lager, may equar the bacteria in total mass.

  40. Fungi • strictly anaerobic. • The fungi are capable of utilizing most polysaccharides • many soluble sugars, but not use the pectin, polygalacturonic acid, arabinose,fucose, mannose and galactose.

  41. As the microbial mass synthesized in the rumen provides about 20 % of the nutrients absorbed by the host animal, the composition of microorganisms is important. • The bacteria dry matter contains about 100 g/kg, but only 80 % of this is in the form of amino acids, the remaining 20% being present as nuclic acid N. • Some of the amino acids are contained in the peptidoglycan of the cell wall membrane and are not digested by the host animal.

  42. Digestion of carbohydrates • All the carbohydrates, but not lignin, are attacked by the rumen microorganism. • The breakdown of carbohydrates in the rumen may be divided into two stages:

  43. First stage: • Digestion of complex carbohydrates to simple sugars (brought by extracellular microbial enzymes). That as analogous to the digestion of carbohydrate in non-ruminants.(Fig. 8.2)

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