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Chapter 18

Chapter 18. The Digestive System. Functions of the GI Tract. Motility : Movement of food through the GI tract. Ingestion: Taking food into the _______________. Mastication: Chewing the food and mixing it with saliva. _______________________: Swallowing the food. Peristalsis:

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Chapter 18

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  1. Chapter 18 The Digestive System

  2. Functions of the GI Tract • Motility: • Movement of food through the GI tract. • Ingestion: • Taking food into the _______________. • Mastication: • Chewing the food and mixing it with saliva. • _______________________: • Swallowing the food. • Peristalsis: • Rhythmic wave-like contractions that move food through GI tract.

  3. Functions of the GI Tract (continued) • Secretion: • Includes both _____________ and endocrine secretions. • Exocrine: • HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin, elastase, and histamine are secreted into the lumen of the GI tract. • Endocrine: • Stomach and small intestine secrete hormones to help regulate the GI system. • Gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, and somatostatin.

  4. Functions of the GI Tract (continued) • Digestion: • Breakdown of food particles into subunits (__________________ structure change). • Absorption: • Process of the passage of digestion (chemical subunits) into the blood or lymph. • Storage and elimination: • Temporary storage and elimination of indigestible food.

  5. Digestive System (GI) • GI tract divided into: • Alimentary canal. • Accessory digestive organs. • GI tract is ______ft long and extends from mouth to anus.

  6. Crop found in birds and other lower animals

  7. Layers of GI Tract • Muscularis. • Serosa. • Composed of 4 tunics: • Mucosa. • Submucosa.

  8. Mucosa • Lines the lumen of GI tract. • Contains: • Connective tissue & lymph nodules. • Thin layer of smooth muscle responsible for the folds. • Goblet cells: • Secrete _______________.

  9. Submucosa • Contains blood vessels, lymph, and nerve fibers • Absorbed molecules enter the blood and lymphatic vessels. • Submucosal plexus (Meissner’s plexus): • Provide autonomic nerve supply to the muscularis mucosae.

  10. Muscularis • Responsible for segmental contractions and peristaltic movement through the GI tract. • Inner circular layer of _________ muscle. • Outer longitudinal layer of smooth muscle. • Contractions of these layers move food through the tract; pulverize and mix the food. • Major nerve supply to GI tract. • Fibers and ganglia from both sympathetic and parasympathetic nervous systems. • Enterogastric Reflex: (_____________)

  11. Enterogastric Reflex: (pacemaker) • Type of food determines rate of passage in gut • High fat meal – may be in GIT ____ or more hours • High COH – may be out by ____ hours

  12. Serosa • Binding and protective outer layer.

  13. Regulation of the GI Tract • Extrinsic innervation: • Parasympathetic nervous system: • Vagus and spinal nerves: • Stimulate motility and GI secretions. • Sympathetic nervous system: • Reduce peristalsis and secretory activity.

  14. _______________: constriction of the guy at one point on its length initiates constriction at a neighboring point – wave • _______________: constrictions of circular muscles appear and disappear in patterns that push the contents back and forth

  15. Regulation of the GI Tract (continued) • Submucosal and myenteric plexuses: • Local regulation of the GI tract. • Paracrine secretion: • Molecules acting locally. • Hormonal secretion: • Secreted by the mucosa.

  16. From Mouth to Stomach

  17. Mouth • Tongue: in herbivores, tongue grasps food and brings it in • Rough surface: papillae, providing traction for moving food • Bringing food into mouth is voluntary

  18. Mouth • ________________: decreases particle size and mixes with saliva which contains salivary amylase. • Enzyme that can catalyze the partial digestion of starch. • Makes food into a bolus • ________________: important in ruminants- (regurgitation) • Ruminants take in large amounts of food in a short period of time

  19. Saliva • Glands: 3 major paired glands in mammals • 1. Parotid: below and front of ear • 2. Mandibular – under jaw • 3. Sublingual – under tongue • Ruminants have 4th: Inferior molar • ____________ – small glands • Saliva – pH = 6-7 • Functions: Lubricant • Dissolves some food • Taste

  20. Saliva • Composition of saliva: • 1. Water: 98-99% • 2. ______________ • 3. ______________________ – starch splitting • found in humans, horses, swine and dogs (not ruminants) • Starts COH digestion • 4. Sodium bicarbonate, phosphate • buffers stomach • Ruminants: large amount of saliva • Important in ___________________recycling

  21. Saliva formation

  22. From Mouth to Stomach • __________________ (swallowing): • Begins as a voluntary activity. • Cannot be stopped. • Larynx is raised. • Epiglottis covers the entrance to respiratory tract.

  23. From Mouth to Stomach (continued) • Esophagus: • Muscular tube – passes through thoracic cavity and diaphragm to the ________ of the stomach • Normally closed, stretches open when a bolus of food passes through • Sits on the _________ side of the trachea • Connects pharynx to the stomach • Can observe bolus transport in cattle

  24. Esophagus • Peristalsis: • Wave-like muscular contractions: • Circular smooth muscle contract behind, relaxes in front of the bolus. • _______________ Sphincter: muscle that opens and closes • Physiological barrier between esophagus and stomach Insert 18.4a

  25. Ruminant Stomach • ________________ animals • Digestive system • Large, lots of space for processing large quantities of bulky forage • 4 chambers of stomach: • __________________________________

  26. 4-compartments of ruminant; only one stomach

  27. Ruminant Stomach • Reticulorumen • @ 1 billion bacteria & 1 million protozoa per milliliter • Large structure for fermentation of cellulose • ________________% of total digestion occurs here • ___________ secretory function • Does have _________________ function • Composed of smooth muscle with vagus innervation • Blood from reticulorumen • portal vein – liver

  28. Digestion in ruminant • Carbohydrates – cellulose • Microbe population • volatile fatty acids (_______________________________) • absorbed across rumen wall • Proteins – digested by _____________ • Lipids – also broken down • Microbes in rumen synthesize all ______complex vitamins and all ____________ amino acids

  29. Ruminant Stomach • __________ – common to both the rumen and reticulum (where they sort of meet) • esophageal groove • Extends from the cardia to the omasum • Formed by two heavy muscles • Can close to allow food to go directly from the esophagus to the _______________ • __________________

  30. Omasum • Epithelium has leaflike folds • Enormous ________________ ability

  31. Abomasum • True stomach • similar to monogastric stomach with some secretory ability • Has a _______________ sphincter

  32. Non- Ruminant Stomach • Most distensible part of GI tract. • Empties into the duodenum. • Functions of the stomach: • ____________________. • Initiates digestion of ____________. • Kills bacteria. • Moves food (chyme) into intestine.

  33. Stomach (continued) • Contractions of the stomach churn chyme. • Mix chyme with gastric secretions. • Push food into intestine. Insert fig. 18.5

  34. Stomach (continued) • Gastric mucosa has gastric pits in the folds. • Cells that line the folds deeper in the mucosa, are gastric glands. Insert fig. 18.7

  35. Stomach (continued) • Non Ruminant Stomach (_________) • Exterior Subdivided into: • 1. Cardia (entrance) • 2. Fundus • 3. Body • 4. Pylorus (termination) (aka: antrum; constricted part) joins to duodenum • Cardia and pylorus act as sphincters to control passage of food

  36. Stomach (continued) • Interior Subdivided into: • 1. Esophageal Region (non glandular; compares to fore-stomaches in rum) • large in horse, small in pig • 2. Cardiac-gland region (sometimes called gastric gland region) • large in pig, smaller in horse • 3. ________________-gland region • 4. Pyloric-gland region • Surface is folded into depressions or gastric pits, increases surface area

  37. Horse Rabbit

  38. Hindgut Fermenters • Both Rabbit and horse are monogastrics • Rabbit – Produce “hard” and “soft” feces • Hard – “rabbit pellets” • Soft – material from _________ this is enclosed in mucous membrane that passes through the hindgut and is eaten by the rabbit as it emerges from the anus

  39. Gastric Glands • Secrete gastric juice: • Goblet cells: mucus. • Parietal cells: _____________________. • Chief cells: pepsinogen. • Pyloric (G cells): gastrin. • Stomach: ______________________.

  40. Parietal cells secrete ________ Chief cells secrete___________

  41. HCl Production (continued) • HCl production is stimulated: • Indirectly by ____________ • Makes gastric juice very acidic. • Makes proteins become more digestible. • Activates pepsinogen to pepsin. • Pepsin is more active at pH of 2.0.

  42. HCl Functions Insert fig. 18.9

  43. Digestion and Absorption in the Stomach • Proteins partially digested by______. • Carbohydrate digestion by salivary amylase is soon inactivated by acidity. • _______________________ are the only commonly ingested substances absorbed.

  44. Protective Mechanisms of Stomach • Parietal and chief cells impermeable to ____. • Alkaline mucus contains HC03-. • Tight junctions between adjacent epithelial cells. • Rapid rate of cell division (entire epithelium replaced in 3 days). • ___________________ inhibit gastric secretions.

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