Gastrointestinal Tract Part 1

FUNCTIONS Prehension Transport, and breakdown of food Mechanical and chemical Absorption of nutrients Elimination of waste from the body Mouth > pharynx > esophagus > stomach > small intestine > large intestine > anus

DIETS OMNIVORES: eat meat and plants (pigs, most bears, chickens, humans, cockroaches, most birds) HERBIVORES: eat plants (cows, horses, rabbits, panda bears) CARNIVORES: eat meat (cats, dogs, polar bears, some plants)

GI STRUCTURES Mouth Teeth Tongue Pharynx Esophagus Stomach Intestines Accessory organs: salivary glands, liver, and pancreas

MOUTH LABIA = lips (entrance to the mouth) Covered with thin skin on outside Some species have tactile hairs bordering lips. Lined by mucous membrane on inside Some animals have specially-adapted lips

Rats have lips that meet behind the incisors so that they can chew through material without having to ingest it.

sheep, goats, horses have soft and flexible lips that help to pick up food CONICAL PAPILLAE – cone-shaped finger-like projections found on the inside of the lips of ruminants. Prevents food from escaping from the mouth.

Lips of cattle and pigs are stiff and do little more than close the mouth

Members of the camel family have deeply split upper lips (philtrum) that allow them to graze close to the ground without disturbing the roots of plants.

ORAL CAVITY – Gums (gingivae) – Teeth (dento- donto-) – Tongue (glosso-) Bounded by lips & cheeks Functions: – Food holder – Food is broken down into smaller particles

PALATE PALATE forms the roof of the mouth: HARD PALATE – – Rigid, bony structure – Covered with mucous membranes with transverse ridges of thickened membrane

PALATE SOFT PALATE – Partition between mouth and nasopharynx – Composed of muscle tissue – Covered with mucous membrane

CHEEKS Controlled by buccinator muscles (keep food between the teeth while chewing) Formed by elastic tissue of mucous membrane covering fatty buccal pad

TONGUE Skeletal muscle Covered by mucous membrane Functions keeps food between the teeth during chewing puts pressure on the hard palate to aid in swallowing used for food prehension licking, grooming, lapping up fluids

What do they use their tongues for?

LINGUAL FRENULUM – anchors underside of tongue to floor of the mouth PAPILLAE – elevations on the sides and upper surface of the tongue

Papillae of the Tongue Filiform: threadlike Fungiform: mushroomlike Vallate: rim shaped The fungiform and vallate contain taste buds.

GINGIVAE / GUMS Forms a collar around each tooth Mucous membranes and fibrous tissue that cover the maxilla and mandible Highly vascular

TEETH Number varies between species and diet Function to cut and grind food and to provide defense DECIDUOUS TEETH – baby teeth which are replaced by PERMANENT TEETH Rabbits and rodents have only one set of teeth that grow throughout life

TEETH CROWN – encased in enamel; HARD – projects above gumline NECK is located in gumline, ROOT – encased in cementum; bonelike – fixes the tooth in the socket (BONY ALVEOLUS)

TEETH DENTIN lies under the enamel and cementum and makes up the bulk of the tooth PULP CAVITY is inside the dentin and contains the tooth’s nerve and blood supply PERIODONTAL LIGAMENT (fibrous tissue) – connects cementum to bone of the alveolus PERIODONTIUM (See next slide)

The Periodontum The periodontium is the area where the tooth meets the gum. It functions to attach the tooth to the jaw and provide support, resistant to normal functional forces. It includes: Gingiva Gingiva Periodontal ligament Periodontal ligament Cementum Cementum Alveolar bone Alveolar bone

HYPSODONT Herbivores have HYPSODONT teeth (highly elevated crown) They do not have a well- defined neck Continue to erupt throughout an animal’s life grooves on surface help to predict an animal’s age HORSES, RABBITS, RODENTS

RAT

BRACHYDONT Carnivores have BRACHYDONT teeth short crown Long, well-developed roots Do not contine to erupt throughout an animal’s life HUMANS, PIGS, CARNIVORES

CANINE

TEETH INCISORS (I) – front teeth that are used for shearing and cutting grass. Can also be used for defense. upper incisors are absent in ruminants, instead, they have a dental pad CANINES (C) – “fangs” “eyeteeth” “tusks” used to tear or for defense prominent in carnivores PREMOLARS (P) – “cheek teeth” Caudal to canines; rostral to premolars MOLARS (M) – grind food to a size that can be swallowed

Maxillary Arcade

Mandibular Arcade

DENTAL FORMULA DENTAL FORMULA: Indicates the number of each kind of tooth on one side of the mouth (I,C,P,M) – Numerator: teeth in the upper jaw – Denominator: teeth in the lower jaw – Multiply the formula by 2 to represent the total number of teeth.

DENTAL FORMULA SpeciesDental FormulaTotal # teeth Canine - puppyi 3/3, c 1/1, p 3/328 (NO MOLARS) Canine - adultI 3/3, C 1/1, P 4/4, M 2/342 (EXTRA MOLAR ON MANDIBLE) Feline - kitteni 3/3, c 1/1, p 3/226 Feline - adultI 3/3, C 1/1, P 3/2, M 1/130 (EXTRA PRE-MOLAR ON MAXILLA) Equine - adultI 3/3, C 1/1, P3-4/3, M 3/340 0r 42 Porcine - adultI 3/3, C 1/1, P 4/4, M 3/344 Bovine adultI 0/3, C 0/1, P 3/3, M 3/332 (NO UPPER INCSORS – DENTAL PAD)

Directional Terminology: Tooth Surfaces Lingual - near tongue Buccal – near cheek Labial – near lips Occlusal – chewing or biting surface Distal – toward throat (away from midline) Mesial – near midline

SALIVARY GLANDS composed of 3 pairs of well-defined glands and a variety of minor saliva secreting tissues. Primary salivary glands: – Parotid – Mandibular – Sublingual Minor salivary glands/tissues: – Labial, buccal, lingual, palatine The dog also has a salivary gland by the eye called the zygomatic gland

SALIVARY GLANDS SALIVA – serous fluid secreted by the salivary glands that functions to: – dissolve or lubricate food – facilitate swallowing – initiate digestion of starches (amylase)

Enlarged Salivary Glands

PHARYNX Common passageway for air and food. Commonly referred to as the throat. Epiglottis closes off airway during swallowing. Covered in previous chapter.

ESOPHAGUS Muscular tube from the pharynx through the diaphragm to the stomach Dilates as food passes through, lumen is typically closed otherwise.

The act of swallowing 3 phases 1.voluntary – passage of food from the mouth to the pharynx. At this point, the larynx is blocked by the epiglottis, so food should only go in the correct direction. Tongue also helps by pressing against the hard palate. 2.involuntary – reflex phase that passes the food from esophagus toward the stomach. Respiration is suppressed as to keep food from going into the trachea. 3.involuntary – muscles contract the food through the cardiac sphincter of the esophagus into the stomach