Comparative Anatomy of Animal Digestive Tracts

Cephalic Tract

The mouth can be a simple opening or have structures that allow for the active capturing of food and the start of chemical and mechanical digestion. Some modifications of the mouth include:

• Mouthparts: Characteristics of arthropods. These pieces are organized around the mouth and differ depending on the food source.
• Beaks: Horny structures consisting of two parts designed to capture and tear food.
• Teeth: In addition to retaining prey, they start the mechanical digestion of food. They are responsible for cutting, tearing, and chewing. These are present in mammals.
• Chelicerae: Nail-like parts found in spiders; they also contain venom used to paralyze prey.

A pouring of mouth secretions comes from the salivary glands. Saliva secretion is composed of water and mucin, which hydrates and lubricates food to encourage swallowing. Additionally, saliva can contain digestive enzymes that initiate chemical digestion.

Foregut (Previous Tract)

The esophagus is a tube that connects the mouth to the stomach, moving food through peristaltic movements. In some animals, a crop is inserted; its function is to act as a food storage area. Another structure, the gizzard, serves to crush food.

The stomach is the most extensive part of the digestive tract. On its walls, there are glands that secrete gastric juice. The stomach can be formed by one cavity (monogastric) or more than one (digastric). Digastric stomachs are typical of herbivores.

Herbivore Stomachs

The stomachs of herbivores have two zones:

• Fermentation: Contains many bacteria that ferment carbohydrates, especially cellulose. Partially digested food from this area returns to the mouth (rumination).
• Digestive: Where typical chemical digestion is performed.

Midgut (Tract Half)

Consisting of the small intestine, which has three parts: the duodenum, jejunum, and ileum. In the small intestine, the following occur:

• Chemical Digestion: Takes place in the duodenum and the first section of the jejunum.
• Absorption: The passage of nutrients into the blood, occurring in the jejunum and ileum.

Hindgut (Subsequent Tract)

Consisting of the large intestine, which has three parts: the cecum, colon, and rectum. In the large intestine, there are bacteria and fungi that produce:

• Vitamins: Essential for the animal.
• Stools: The final waste product.