The Digestive System

Chapter 11

Introduction to Digestive System

AKA: Digestive tract, gastrointestinal tract, GI tract, Alimentary canal, gut

System that takes complex food and breaks it 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.

Tube with a LUMEN that runs from the mouth to the anus. Accessory digestive organs aid in the process of digestion and absorption.

Salivary glands, liver, and pancreas

Species Variation Requirements for digestion

and absorption of foodstuffs vary depending on diet ____vores - plant-eating

animals ____vores - meat-eating

animals ____vores - eat plant

material and meat

______________ animals - simple (single) stomachs

______________ - multiple compartments

Function of GI tract

1. Prehension (grasping) of food with the lips or teeth

2. Mastication - mechanical grinding and breaking down of food (chewing)

3. Chemical digestion of food

4. Absorption of nutrients and water

5. Elimination of wastes

Digestive Tract Structure

Four layers:

_____________ –lining; consists of the epithelium and some loose connective tissue

_____________ - beneath the mucosa; made of dense connective tissue.contains glands

_____________- circular and longitudinal muscle layers

_____________- outermost layer

Digestive Tract Structure

______________ - Sheets of connective tissueSuspends intestines from dorsal body wall Contains blood vessels, lymph vessels, and nerves that

supply GI tract

Digestive Tract Epithelium

________ ________ epithelium

Thick and tough Lines mouth, pharynx,

esophagus, and anus

________ ________ epithelium

From junct of esoph/stom to junct of rectum/anus

Nutrients are absorbed through this thinner epithelium

Digestive Tract Musculature

Skeletal muscle - voluntary control

Mouth, pharynx, cranial esophagus, ext anal sphincter

Facilitates chewing, mixing saliva with food, initiation of swallowing, and control of defecation

Smooth muscle

Majority of esophagus, stomach, s. intestines, l. intestines, and internal anal sphincter

Primarily arranged in circular and longitudinal layers Contraction of circular muscle fibers

__________ tract Contraction of longitudinal fibers

__________ tract

Peristalsis

Circular muscle contractions

Wavelike movement along tract

________ contents along digestive tract

Segmental Contractions

Periodic circular muscle contractions

Occur in different adjacent sites

_______ digestive tract contents and slows their movement through tract

Salivary glands - saliva helps with evaporative _________, __________, and ___________; usually three pairs with ducts to oral cavity

_________ salivary glands - ventral to ear canals

__________salivary glands - ventral to parotid glands at the caudal angle of the mandible

____________ salivary glands - medial to the shafts of the mandible just under the base of the tongue

SALIVARY GLANDS

Teeth• Incisors, Canines, Premolars, and Molars are found in both herbivores and carnivores

• _______________ - chewing; physically break down food into smaller pieces • Increases the surface area of the food that is exposed to digestive processes

• _________ arcade – teeth in maxilla and incisive bones

• _________ arcade – teeth in mandible

Teeth: Shape

Carnivore teeth - _________ on occlusal surface; slightly curved toward back of mouth

Good for holding prey, tearing, cutting, shredding

Herbivore teeth - ________ occlusal surfaces

Good for grinding plant and grain material

Types of Teeth

Incisors _____________

teethMost rostral teeth

of upper and lower arcade

Canines_____________

teethLocated at corners

of incisors Longer than other

teeth Pointed at tip

** Ruminants lack upper incisors AND canines. They have a _________ _____ instead**

Types of Teeth

Premolars_____________ teeth Rostral cheek teethSharp points and surfacesin carnivores

Molars____________ teethCaudal cheek teeth Larger, flatter occlusal surfaces

Species Dental Formula Total Number of Teeth

Canine - puppy i3/3 c1/1 p3/3 28Canine - adult I3/3 C1/1 P4/4 M2/3 42Feline - kitten i3/3 c1/1 p3/2 26Feline - adult I3/3 C1/1 P3/2 M1/1 30Equine - adult I3/3 C1/1 P3-4/3 M3/3 40 or 42Porcine - adult I3/3 C1/1 P4/4 M3/3 44Bovine - adult I0/3 C0/1 P3/3 M3/3 32

Dental Formulas for Several Domestic Species

Dogs: 1st Molar in lower arcade and 4th Premolar in upper arcade

Abscesses that form at the root of the apex of the upper carnassial tooth often break through the thin bone of the maxilla and begin to drain through the skin below the eye. Removing the carnassial teeth is

difficult due to their deeply entrenched roots

Carnassial Teeth