The Digestive System

1. The Digestive System Chapter 11

2. Introduction • 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, or gut.

3. Lumen • 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. • Why? • What must occur for things to enter the body?

4. 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 the digesting and absorbing chores. • Herbivores • Plant eating animals • Carnivores • Meat eating animals • Omnivores • Animals tat eat both plants and meat.

5. Types of Stomachs • Monogastric • Animals that have simple, single stomachs. • Complex Stomachs • Animals that have fermentation compartments in addition to the stomach. • Example is ruminant animals.

8. Function of 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, then malnutrition may result. • Usually failure is followed by clinical signs. • Examples of clinical signs?

9. Terminology • Gastro- refers to the stomach. • Entero- refers to the intestine.

10. 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 outside the submucosa. • What type of muscle is this? • The serosa- is the outermost layer that consists of a thin, tough layer of connective tissue.

12. 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

13. Epithelium of the Digestive Tract • 2 types • Stratified Squamous • Thick and tough. • Lines mouth, pharynx, esophagus, and anus. • Simple Columnar • Change occurs where esophagus enters stomach. • Allows for better absorption of nutrients.

15. 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.

17. How food is moved? • Moved and mixed by two types of muscle contractions. • Peristalsis contractions • Move contents along digestive tract. • Circular muscle contractions that move food along in waves. • Propel food ahead of contractions.

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19. Food Movement continued • 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.

20. Mouth or Oral Cavity • Also called the buccal cavity. • Where food is initially taken in and where digestion actually begins. • Structures include: • Lips • Prehensile organ • Labial- 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

21. Salivary glands continued • 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?

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

23. 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.

25. 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

27. Teeth shape • 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

30. 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

32. Dental Formula • Typical number of each type of tooth found in upper/lower arcades • Tooth type designate • 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.

34. 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

35. Numerical Dental Charting • Each quadrant of the dental arcade is assigned a particular number. • Upper right quadrant is 100 • Upper left quadrant is 200 • Lower left quadrant is 300 • Lower right quadrant is 400 • Each tooth is assigned a number according to position.

38. Teeth continued • 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.

41. 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

42. Teeth Structure continued • Apex • Remember the pointy part • 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

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

44. Functions of the Oral Cavity • Prehend 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.

45. 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. • How do we recognize? • 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.

46. Digestive Enzymes Continued • 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.

47. Esophagus • Tube that extends from pharynx to the stomach. • Function is to take swallowed material to the stomach. • No digestion takes place, serves only for transport. • Enters the cardia of the stomach. • The cardiac sphincter surrounds the cardia. • Esophagus enters stomach at an angle. • This allows that as the stomach fills with food, can close off against esophagus decreasing chance of reflux. • What is reflux? • Which animals can not vomit? • Why?

49. Swallowed Corrosive Material • If a dog or cat swallows a corrosive material, why do we not initiate vomiting? • If corrosion is significant, then can cause perforation- a tear or hole within the esophagus. • Perforation can cause food to enter thoracic cavity.

50. Megaesophagus • When esophagus loses muscle tone. • Food accumulates in the esophagus instead of being transported to stomach. • How do we treat? • Feed liquid based diet • Feed on an elevated surface • Holding animal up and allowing gravity to pull food down to stomach. • Can lead to aspiration pneumonia.