CHAPTER OUTLINE

■ INTRODUCTORY CONSIDERATIONS

■ THE ORAL CAVITY AND PHARYNX

Teeth

Tongue

Pharynx

■ THE SIMPLE STOMACH

Esophagus

Stomach

■ INTESTINES

Small Intestine

Large Intestine

■ ACCESSORY ORGANS

■ COMPOSITION OF FOODSTUFFS

Carbohydrates

Proteins

Lipids

Accessory Foods

■ Pregastric mechanical functions

Prehension

Mastication

Deglutition

■ GASTROINTESTINAL MOTILITY

Segmentation and Peristalsis

■ MECHANICAL FUNCTIONS OF THE STOMACH AND SMALL INTESTINE

Delay of Gastric Emptying

Emesis

Mechanical Functions of the Small Intestine

■ MECHANICAL FUNCTIONS OF THE LARGE INTESTINE

Defecation

Intestinal Transport of Electrolytes and Water

■ DIGESTIVE SECRETIONS

Saliva

Gastric Secretions

Pancreatic Secretions

Biliary Secretions

■ DIGESTION AND ABSORPTION

Carbohydrates

Proteins

Fats

Microbial Digestion in the Large Intestine

■ THE RUMINANT STOMACH

Structure and Function

■ CHARACTERISTICS OF RUMINANT DIGESTION

Rumination

Gas Production and Eructation

■ CHEMISTRY AND MICROBIOLOGY OF THE RUMEN

■ RUMINANT METABOLISM

Gluconeogenesis

Energy Production

Ruminant Ketosis and Bloat

■ AVIAN DIGESTION

The Digestive Tract

The maintenance of life requires that animals obtain nutrients essential for the body processes from food. Animals can live for a period of time without food; in such a situation, the body stores of energy and finally the tissues themselves are broken down and metabolized through biochemical conversion.

It is generally believed that food is in the body after its acquisition and ingestion, but the digestive tract is a hollow, tube-like structure that extends from the mouth to the anus, so materials within its lumen are still, strictly speaking, outside the body. Therefore, the acquisition of food must be followed by processes that divide food into smaller parts through both physical and chemical means, so that the structural units or other simple chemical compounds can finally enter the body by crossing the intestinal barrier. The process associated with this division (or, as often stated, degradation of food to more basic units) is called digestion and the process of crossing the intestinal epithelium and entering the blood is called absorption. The reactions and conversions necessary to provide energy, build tissues, and synthesize secretions constitute intermediary metabolism. The continuance of intermediary metabolism in the body depends on digestion and absorption.

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