Accessory Organs and GI Tract

Digestive System

• The anal columns and sphincters help regulate defecation.
• Ingestion, digestion, and secretion occur in the digestive system, followed by absorption for transport to other tissues.

Accessory Organs

• Salivary glands (parotid, sublingual, and submandibular) secrete saliva that lubricates and moistens food and contains amylase for carbohydrate digestion.
• The liver synthesizes bile, which is stored and regulated by the gallbladder.
• The pancreas releases pancreatic juice containing amylase, trypsin, and lipase.

Absorption

• Capillaries transport water-soluble nutrients.
• Lacteals are responsible for transporting glycerol and fatty acids.
• The digestive system takes nutrients from digested food for transport to different tissues.

Human Digestive System

• The mouth is a site for both mechanical and chemical digestion.
• The tongue is a muscular organ for tactility and gustation.
• Humans have 32 teeth that physically break down food.
• The pharynx is a tube that connects the mouth and esophagus, with nasopharynx and oropharynx portions.

Enzymes

• Bile is responsible for fat emulsification.
• Amylase is responsible for starch digestion.
• Trypsin is responsible for protein digestion.
• Lipase is responsible for lipid digestion.
• Nuclease performs nucleic acid digestion.

Ruminant Digestive System

• Ruminant ingests food rich in cellulose.
• Mechanical digestion and exposure to cellulase occur in the rumen.
• The reticulum helps in regurgitation of food.
• The omasum performs further mechanical digestion.
• The abomasum performs the final digestion.

Ruminant Animals

• Examples of ruminant animals include hog deer, cattle, camel, and sheep.

Fish Digestive System

• Bony fishes engulf water and trap particles with gill rakers.
• Food moves to the esophagus and stomach.
• The pylorus leads to the pyloric cecum.
• The pancreas secretes proteases, lipases, and carbohydrases.
• Nutrient absorption occurs in the intestines.

Avian Digestive System

• During ingestion, birds do not chew their food.
• Food moves to the crop, where it can still be regurgitated.
• The enzymes of the proventriculus facilitate chemical digestion.
• The gizzard facilitates mechanical digestion of food.
• Food wastes and urine have a common exit point, the cloaca.

Avian Examples

• Examples of birds with unique digestive systems include hummingbirds and penguins.
• Parent birds can store food in their crop for regurgitation upon return to their nests.