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 1 st 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