The Digestive System

Functions

• Ingestion (eating)

• Grinding

• Digestion

• Absorption of nutrients

• Elimination of solid wastes

Introduction

• Digestive system changes food nutrients into compounds easily absorbed by the body

• Nutrients are used for:– Energy, growth and maintenance

Definitions

• Herbivores– Depend entirely on plants for food source– Ex. Cattle, sheep, horses, rabbits

• Carnivores– Depend primarily on flesh of other animals– Ex. Dogs and cats

• Omnivores– Consume both flesh and plants– Ex. Swine, poultry, humans

Digestive Tract

• Extends from the lips to the anus

• Length of digestive tract depends upon the specie– Carnivores is usually short, herbivores is long

• Simple and complex stomachs

Mouth

• Primary functions– Prehension

• Grasping of food

– Grinding of feed– Mixing feed and saliva

Teeth

• Responsible for grinding

• Incisors are used for cutting food

• Premolars and molars are responsible for grinding

• Milk teeth– Lost and replaced by permanent teeth

Tongue

• Used in prehension

• Aids in chewing process

• Mass of muscles covered by a membrane

• Covered with papillae which contain the taste buds

Lips

• Horses and sheep– Used in grasping feed– Used in sorting through feed

• Swine and cattle– Keep mouth closed

Other Mouth Parts

• Cheeks– Lines food up with the teeth

• Jaw – Lined with powerful muscles that aid in

chewing

• Hard Palate– Roof of the mouth

• Soft Palate– Divides pharynx and oral cavity

Salivary Glands

• Common in the mucous lining of the mouth

• Except for:– Tongue– Hard palate– Gums

Pharynx

• Common passageway for air and food

• Several structures open into pharynx:– Mouth, nasal cavity, Eustachian tubes, larynx,

and esophagus

• Pushes food into the esophagus

Esophagus

• Connects the pharynx to the stomach

• Walls have two layers of muscles– Muscles run at right angles to each other

Non-Ruminant Stomach

• Consist of only one compartment

• Called the ‘true stomach”

• On the left side of the body

• High surface area due to folding

• Gastric glands produce:– Hydrochloric acid– Enzymes:

• Pepsin and rennin

Ruminant Stomach

• 4 parts:– Rumen, reticulum, omasum, abomasum

• 1st three parts contain no glands, they soak food and allow for microbial digestion

• Reticulum– Forward most portion– Honeycomb-like

Ruminant Stomach

• Rumen– Fills most of the left side of the abdomen– 2 parts: dorsal and ventral– Consist of two layers of smooth muscle– Mature ruminants: rumen accounts for 80% of

the total stomach

Ruminant Stomach

• Omasum– Round in shape– Contains many small papillae which grind

roughage

• Abomasum– Only glandular stomach– Similar to a non-ruminant stomach

Small Intestine

• 3 parts:– Duodenum

• Digestive juices from pancreas and liver

– Jejunum– Ileum

Large Intestine

• Consists of:– Cecum

• Shaped like a comma• Varies drastically in size across species

– Horses and rabbits have largest ceca

– Blind pouch– Colon– Anus

Poultry Digestive System

• Don’t have teeth

• Crop– Stores and softens food

• Gizzard– Grinds food– Contains grit and gravel

• Proventriculus– Glandular stomach

Pancreas

• Exocrine functions– Produces digestive

juices

• Endocrine– Produces insulin

Liver

• On the right side of the body

• Purifies blood

Gallbladder

• Attached to the liver• Produces bile• Green organ