Introduction

The Digestive System

• Most nutrients we eat cannot be used in existing form – Must be broken down into smaller components before body can make use of them

• Digestive system—acts as a disassembly line
– To break down nutrients into forms that can be used by the body
– To absorb them so they can be distributed to the tissues

• Gastroenterology—the study of the digestive tract and the diagnosis and treatment of its disorders
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Digestive Function

Digestive Function
• Digestive system—organ system that processes food, extracts nutrients, and eliminates residue

• Mechanical digestion—the physical breakdown of food into smaller particles

• Five stages of digestion
– Ingestion: selective intake of food
– Digestion: mechanical and chemical breakdown of food into a form usable by the body
– Absorption: uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph
– Compaction: absorbing water and consolidating the indigestible residue into feces
– Defecation: elimination of feces

– Cutting and grinding action of the teeth
– Churning action of stomach and small intestines
– Exposes more food surface to digestive enzymes

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General Anatomy

Digestive Function
• Chemical digestion—a series of hydrolysis reactions that breaks dietary macromolecules into their monomers (residues)

• Digestive system has two subdivisions: digestive tract and accessory organs
• Digestive tract (alimentary canal) – Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine
– Results
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– 30 ft long muscular tube extending from mouth to anus – Mouth, pharynx, esophagus, stomach, small intestine, and large intestine
– Gastrointestinal (GI) tract is the stomach and intestines Polysaccharides into monosaccharides
Proteins into amino acids
Fats into monoglycerides