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• 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: threadlikeFungiform: mushroomlike

Vallate: rim shapedThe 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

http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/dentalanat.html

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:• GingivaGingiva• Periodontal ligamentPeriodontal ligament• CementumCementum• Alveolar boneAlveolar 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 FORMULASpecies Dental Formula Total # teeth

Canine - puppy i 3/3, c 1/1, p 3/3 28 (NO MOLARS)

Canine - adult I 3/3, C 1/1, P 4/4, M 2/3 42 (EXTRA MOLAR ON MANDIBLE)

Feline - kitten i 3/3, c 1/1, p 3/2 26

Feline - adult I 3/3, C 1/1, P 3/2, M 1/1 30 (EXTRA PRE-MOLAR ON MAXILLA)

Equine - adult I 3/3, C 1/1, P3-4/3, M 3/3 40 0r 42

Porcine - adult I 3/3, C 1/1, P 4/4, M 3/3 44

Bovine adult I 0/3, C 0/1, P 3/3, M 3/3 32 (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