Section 2

Digestive System

• Mechanical digestion involves the breaking of food into smaller particles. Chemical digestion involves changing the chemical nature of the food substance.

• The mouth, teeth, and tongue initiate mechanical digestion. Chemical digestion of carbohydrates begins in the mouth.

• The esophagus is a passageway through which food passes from the mouth to the stomach by peristalsis.

• The stomach has layers of muscles that churn the food to assist in mechanical digestion. Pepsin in the stomach begins the chemical digestion of proteins.

Vocabulary digestion (p. 985) gastrointestinal tract (p. 985) saliva (p. 986) pharynx (p. 986)

epiglottis (p. 986) peristalsis (p. 987) gastric fluid (p. 988) ulcer (p. 988)

• Bile assists in the mechanical digestion of lipids. Enzymes secreted by the pancreas complete the digestion of the chyme.

• The digested nutrients are absorbed through the villi of the small intestine.

• The large intestine absorbs water from the undigested mass. The undigested mass is eliminated as feces through the anus.

cardiac sphincter (p. 988) chyme (p. 988) pyloric sphincter (p. 988) gallbladder (p. 989)

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