VMBO Year 2 · HAVO/VWO Years 2–3 · Nutrition and digestion · Section 2.2

The digestive system

Digestion

The alimentary canal runs from the mouth to the anus. Together with associated organs, it forms the digestive system, which processes food and enables nutrient absorption.

Small substances, such as glucose, water, minerals and many vitamins, can be absorbed without first being broken into smaller molecules. Proteins, fats and larger carbohydrates, such as starch and many sugars, need digestion first.

Digestion has two aspects:

• Mechanical digestion: Physically breaking food into smaller pieces, for example by chewing.
• Chemical digestion: Breaking large nutrient molecules into smaller ones using digestive enzymes.

Chewing

Teeth carry out mechanical digestion in the mouth:

• Incisors: Bite off pieces of food.
• Canines: Pointed teeth helping grip and tear food.
• Premolars and molars: Crush and grind food with their broad, uneven surfaces.

Chewing makes food easier to swallow and increases its surface area, allowing enzymes to act more effectively.

Digestive juices

Digestive glands produce juices such as saliva and gastric juice. They include:

• Salivary glands.
• Gastric glands in the stomach wall.
• The liver.
• The pancreas.
• Glands in the intestinal wall.

Many digestive juices contain enzymes that speed up chemical reactions and break nutrients into smaller products of digestion. Bile helps digestion but contains no digestive enzymes.

Peristalsis

The wall of the alimentary canal contains circular muscles and longitudinal muscles. Coordinated waves of contraction and relaxation produce peristalsis.

These movements move food along, mix it with digestive juices and help churn the contents. Dietary fibre supports normal bowel function and movement.