Comparative Digestion Systems
&Process
Modified by Ashlee Gibson

The Digestion Process
• Food is broken down
• Animals have digestive systems adapted to the foods that they consume
• Four types of digestive systems
– Ruminant(polygstric)
– Simple Stomach(monogastric)
– Avian
– Equine-modified simple stomach

Ruminant Digestive System
Modified to handle the breakdown of large amounts of fiber

Ruminant Digestive System
• Mouth
– no upper incisors, hard palate
– molars for grinding coarse vegetation
– saliva does not contain enzymes
• Esophagus
– muscular tube connecting the mouth to the stomach

Ruminant Digestive Systems
The Four Compartmented Stomach
• Rumen: storage area and fermentation vat
• Reticulum: nails and wire may be found here-hardware stomach
• Omasum: eliminates excess water from feed
• Abomasum: true stomach, gastric juices and enzymes are secreted

Ruminant Digestive Systems
Stomach (cont.)
• Regurgitation: first step in rumination
– large quantities of roughage are consumed and are chewed just enough to swallow
– after swallowing, regurgitation (“cud chewing”) takes place, food is re-chewed

Ruminant Digestive System
• Small Intestine
– connects stomach to large intestine
– food nutrients absorbed into blood
– contains bile and pancreatic juices
– pushes food through by muscle contractions

Ruminant Digestive System
• Large Intestine
– Contains Cecum, Colon and Rectum
• Cecum: sac at junction of small intestine and large intestine
• Colon and rectum: at end of system
– not as long as small intestine, but larger in diameter
– water and some nutrient absorption occurs here
– where residue solidifies before excretion

Monogastric Digestive System
Characterized by inability to digest roughage efficiently

Monogastric Digestive System
• Mouth
– has upper and lower incisors
– digestive enzymes secreted which breaks down nutrients
• Esophagus
– connects mouth to stomach

Monogastric Digestive System
• Stomach
– secretes Hydrochloric Acid to break down nutrients
– enzymes such as pepsin also secreted here
– churning action mixes food
– small and large intestine
• function just as in ruminant systems

Avian Digestive Systems
Characterized by several organs not found in other species that are adapted for grinding hard or encased food

Avian Digestive Systems
• Mouth
– no teeth which leads to the saying “scarce as a hen’s teeth!!”
– Salivation excretion moistens food
• Esophagus
– has a modification called the “crop” which stores and moistens food
– connects mouth and stomach

Avian Digestive Systems
• Stomach
– Contains two parts
• Proventriculus:same as monogastric stomach and provides digestive excretions
• Gizzard: located after proventriculus, very muscular, used to grind food

Avian Digestive Systems
• Small Intestine
– similar functions as in ruminants and monogastric systems
• Large Intestine
– similar functions as in ruminants and monogastric systems
– “cloaca”: chamber into which urinary and genital canals open
– “ceca”: aids in fiber digestion and absorption

Equine Digestive Systems
Characterized by non-ruminant animals that consume and digest feeds high in fiber

Equine Digestive Systems
• Mouth
– intact top and bottom incisors
– molars adapted to chewing fibrous feeds
– no digestive enzymes in saliva
• Esophagus
– not well adapted for regurgitation
– connects mouth and stomach

Equine Digestive System
• Stomach
– similar to monogastric system
• Small intestine
– similar to monogastric and ruminant systems
– no gall bladder to store bile
– enlarged cecum to aid in fiber breakdown

Equine Digestive System
• Large Intestine
– similar to monogastric systems
– cecum (at junction of small and lare intestines) and colon take up most of the volume of the equine digestive system

Accessory Organs
Organs that aid in the digestive process without actually being part of the digestive system

Accessory Organs
• Pancreas
– produces and secretes digestive enzymes
– produces insulin which regulates carbohydrate metabolism
• Liver
– produces bile-breaks down fatty acids
– stores iron, handles fats and carbohydrates in the blood

References
• Human Biology
– http://ultranet.com/~jkimball/Biologypages/G/GITract.html