EAT! ENJOY!

1. EAT! ENJOY! “We must have pie. Stress cannot exist in the presence of a pie.” David Mamet

2. The Digestive System Chapter 11

3. Introduction to the Gastrointestinal Tract • Takes complex food and breaks them down into simple nutrient molecules through process of digestion. • After digestion takes place, nutrient molecules are absorbed into the bloodstream for use by the body’s cells. • Consists of a tube that runs from the mouth to the anus and accessory digestive organs that aid in the process of digestion and absorption. • Known as digestive tract, Gastrointestinal (GI) tract, the alimentary canal, gastroenteric tract, or gut.

4. Lumen of the Gastrointestinal Tract • The lumen is the opening in the middle of the intestinal tract or any hollow organ. • Anything in the lumen is considered outside the body. • What must occur for things to enter the body?

5. Animal Diets • The requirements for digestion and absorption of foodstuffs vary considerably depending on the diet of the animal. • Each type of animal has different mechanisms to handle digestion and absorption. • Herbivores • Plant eating animals • Carnivores • Meat eating animals • Omnivores • Animals that eat both plants and meat.

6. Classification of the Stomach • Monogastric • Animals that have simple, single stomachs. • Complex Stomachs • Animals that have fermentation and mixing compartments in addition to the stomach.( Ex: ruminants)

7. Functions of the GI tract • Prehension (grasping) of food with the lips or teeth • Mastication - mechanical grinding and breaking down of food (chewing) • Chemical digestion of food • Absorption of nutrients and water • Elimination of wastes • If any function fails, malnutrition may result. • Usually failure is followed by clinical signs. • Examples of clinical signs?

8. GI Terminology • Gastro- refers to the stomach. • Entero- refers to the intestine.

9. GI tract structure • Made of multiple layers. • The mucosa-the lining layer and consists of the lining epithelium and some loose connective tissue • The submucosa-beneath the mucosa and contains glands and dense connective tissue. • The thick muscle layer is external to the submucosa. • What type of muscle is this? • The serosa- is the outermost layer that consists of a thin, tough layer of connective tissue.

10. GI Tract Structure

11. Digestive Tract Structure • Mesentery - Sheets of connective tissue • Suspends digestive tube from dorsal body wall • Contains blood vessels, lymph vessels, and nerves that supply GI tract

12. Epithelium of the Digestive Tract • 2 types of epithelium are found in the GI tract: • Stratified Squamous • Thick and tough. • Lines mouth, pharynx, esophagus, and anus. • Simple Columnar • Change form stratified squamousoccurs where esophagus enters stomach. • Allows for better absorption of nutrients.

13. SIMPLE COLUMNAR EPITHELIUM W/GOBLET CELLS AND MICROVILLI STRATIFIED SQUAMOUS EPITHELIUM

14. Muscle of the GI tract • 2 types • Skeletal Muscle • Under voluntary control • Mouth, pharynx, cranial esophagus, external anal sphincter. • Allows process of chewing, mixing saliva with food, and swallowing to be conscious acts. • Controls defecation. • Smooth Muscle • Present in remainder portion of digestive tract. • Arranged in circular and longitudinal layers. • Circular Layer- narrows segment of tube. • Longitudinal Layer- shortens segment of tube.

15. GI Tract Structure

16. How food is moved through the GI tract • Food is moved and mixed by two types of muscle contractions. • Peristaltic contractions • Move contents along digestive tract. • Circular muscle contractions that move food along in waves. • Propels food ahead of contractions.

17. http://www.youtube.com/watch?v=h0E9ITyRlh0

18. How food is moved through the GI tract • Segmental contractions • Cause back and forth mixing movements of the digestive tract contents. • Consist of periodic, circular muscle contractions that occur in different adjacent sites. • Aid in digestion and absorption by mixing the digestive tract contents and slowing their movement through the tract.

19. Mouth/Oral Cavity • Also called the buccal cavity. • Where food is initially taken in and where digestion actually begins. • Structures include: • Lips • Prehensile organ • Labia- term for referring to the lips. • Tongue • Teeth • Salivary glands • Produce saliva, which performs digestive and lubrication functions. • Also involved in evaporative cooling. • Hard palate • Soft palate • Oropharynx

20. Salivary glands • Most animals have 3 matching pairs of glands. • Parotid salivary glands • Located just ventral to ear canals • Mandibular salivary glands • Located ventral to parotid glands at the caudal angle of the mandible • Sublingual salivary glands • Located medial to the shafts of the mandible just under the base of the tongue. • All have ducts that carry saliva to oral cavity. • Salivary glands are controlled by autonomic nervous system • What happens during “fight or flight”?

21. Parotid salivary glands • Mandibular salivary glands • Sublingual salivary glands • Buccal salivary glands

22. Teeth • Responsible for breaking down food into smaller pieces by process of mastication. • Increases surface area of the food that is exposed to digestive processes. • Maxilla contains upper arcade • Mandible contains lower arcade.

24. Terminology of Teeth Surfaces • Lingual (tongue)- inner surface of lower arcade • Palatal (hard palate)- inner surface of upper arcade • Labial (lips)- outer surface of upper/lower arcades (rostral) • Buccal(cheek) - outer surface of teeth (caudal) • Occlusal – surface that grinds with other teeth

25. Shapes of Teeth • Carnivore teeth - pointed on occlusal surface; slightly curved toward back of mouth • Good for holding prey, tearing, cutting, shredding • Herbivore teeth - flat occlusal surfaces • Good for grinding plant and grain material

26. Tooth Structure

28. Types of Teeth • Incisors • Grasping teeth • Most rostral teeth of upper and lower arcade • Canines • Tearing teeth • Located at corners of incisors • Longer than other teeth • Pointed at tip • Premolars • Cutting teeth • Rostral cheek teeth • Sharp points and surfaces in carnivores • Molars • Grinding teeth • Caudal cheek teeth • Larger, flatter occlusal surfaces • Used for grinding

30. Dental Formula • Typical number of each type of tooth found in upper/lower arcades • Tooth type designated by the following letters: • I=incisor • C=canine • P= premolar • M=molar • Upper case: adult teeth • Lower case: deciduous teeth • Ruminants have no upper incisors or canine teeth. Instead have a dental pad- a flat, connective tissue structure of the maxilla opposite the lower incisors and canine teeth.

31. Dental Formulas of Common species • Species Dental Formula Total Canine - puppy i3/3 c1/1 p3/3 28 • Canine - adult I3/3 C1/1 P4/4 M2/3 42 • Feline - kitten i3/3 c1/1 p3/2 26 • Feline - adult I3/3 C1/1 P3/2 M1/1 30 • Equine - adult I3/3 C1/1 P3-4/3 M3/3 40 or 42 • Porcine - adult I3/3 C1/1 P4/4 M3/3 44 • Bovine - adult I0/3 C0/1 P3/3 M3/3 32

34. Teeth • The fourth premolar is also referred to as the carnassial tooth. • If this tooth abscesses may cause drainage through the skin under the eye. • Because of root system and length of roots, removal is hard work.

35. CARNASSIAL TOOTH ROOT ABSCESS

36. Structure of Teeth • Living structures. • Have nerve, blood vessel and lymph supply. • Are susceptible to damage and pain. • Consist of: • Apex • Pulp • Dentin • Cementum • Enamel • Gingiva

37. Teeth Structure • Apex • the pointed part at the tip of the root • Where blood and nerve supply enter the tooth • Pulp • The center of the tooth • Dentin • Surrounds the tooth pulp. • More dense than bone but less dense than enamel. • Cementum • Hard connective tissue that helps to fasten tooth in bony socket. • Enamel • Hardest, toughest tissue in body. • Outer cover of crown of tooth • Gingiva • Epithelial tissue that forms the gums around the teeth

38. Dental Prophylaxis • The scaling away of tartar from the teeth. • Horses get teeth “floated”-this reduces points on buccal edge of teeth.

39. Functions of the Oral Cavity • Prehension of food • Initiate mastication • Also referred to as mechanical digestion • Initiate chemical digestion • Saliva has enzymes that aid in breakdown of food. • Prepare food for swallowing.

40. Digestive Enzymes • Proteins that promote the chemical reactions that split complex food molecules up into simpler compounds. • Secreted in the digestive system to break down different components of food. • Two common Digestive enzymes: • Amylase • Found in saliva of omnivores but absent in carnivores • Breaks down amylose- a sugar component of starch. • Lipase • Digests lipids • Found in saliva of young animals while nursing or on high milk diet.

41. Digestive Enzymes • Cattle use sodium bicarbonate and phosphate buffers in saliva to neutralize acids that form in rumen. • Cattle can produce 25 to 50 gallons of saliva a day.

42. Esophagus • Tube that extends from pharynx to the stomach. • Function is to take swallowed material to the stomach. • No digestion takes place here, it serves only for transport. • Enters the cardiaof the stomach. • The cardiac sphincter surrounds the cardia. • Esophagus enters stomach at an angle. • As the stomach fills with food, the folds in the stomach can close off against esophagus decreasing chance of reflux.

43. Monogastric (Simple) Stomach • Divided into five different areas. • 1. Cardia • 2. Fundus • 3. Body • 4. Pyloric antrum • 5. Pylorus

44. Stomach • Cardia • Where esophagus enters stomach. • Helps reduce reflux • Fundus & Body • Forms a pouch that can distend as more food is swallowed • Rich with glands • Pyloric Antrum • Distal part of the stomach that grinds food. • Regulates hydrochloric acid • Pylorus • Sphincter that regulates movement ofdigestedstomach contents (Chyme) from stomach to duodenum (first part of intestine). • Prevents backflow of duodenal contents into the stomach.

45. Gastric Glands • Contain 3 key cells: • Parietal cells (oxyntic cells) • Produce hydrochloric acid (HCl) • Chief cells • Produce pepsinogen, precursor to pepsin • Mucous cells • Produce mucus that is protective in nature.

46. Pyloric Antrum glands • G- cells • Endocrine cells • Secretes gastrinhormone • Presence of food stimulates G-cells to dump gastrin into the blood.

47. Stomach shape • C-shaped • Inside called lesser curvature of the stomach. • Outside called greater curvature of the stomach. • Rugae- long folds in the stomach. • Gastritis- inflammation of the stomach. • Gastric ulcers- erosions of epithelium of stomach.

49. Gastric Motility • Each part of the stomach has different muscle functions. • Fundus and body relax with swallowing, allowing stomach to distend and fill with food. • Body of stomach contracts to help mix food within the stomach. • Pyloric Antrum increases contractions with the swallowing of food. • Grinds food and propels food toward pylorus.

50. Empty vs. Full Stomach