The Structure of the Digestive System

Key Points

• The digestive system breaks down food into tiny particles absorbed into the blood.
• These particles provide energy for growth, repair, and maintaining health.
• Food that cannot be broken down is excreted as feces.

Digestive System Activity

• Interactive game available to explore food processing in the human body.

Parts of the Digestive System and Their Functions

• Mouth: Starts digestion by breaking down food with teeth and saliva.
• Oesophagus: A tube connecting the mouth to the stomach.
• Liver: Releases bile into intestines to break down food.
• Stomach: A muscular bag that mixes food and drink with acid.
• Pancreas: Releases enzymes into intestines to break down carbohydrates, proteins, and lipids.
• Small Intestine: Further digestion of proteins and lipids occurs; nutrients absorbed into the blood.
• Large Intestine: Absorbs water from undigested food.
• Rectum: Stores undigested food as feces.
• Anus: The exit point for feces from the body.

Fun Fact

• The mouth produces about 1.5 liters of saliva daily.

Process of Digestion

Mechanical and Chemical Digestion

• Mechanical: Teeth grind food.
• Chemical: Enzymes break food into nutrients.
• Bile: Produced by the liver, stored in the gall bladder, breaks down lipids into smaller droplets (increases enzyme surface area).

Movement of Food

• Food is moved through the digestive system by muscle contractions (peristalsis).
• A tennis ball squeezed through tights can model this process.

Absorbing Food and Water

• Intestines have folds, increasing surface area for absorption.
• Villi: Specialized small intestine structures that absorb digested food.

Fun Fact

• The small intestine's surface area is equivalent to a tennis court when fully extended.

Quiz and Test Questions

1. Order of Digestive System Parts

   • Mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus.

2. Functions of Digestive System Parts

   • Large intestine: undigested food passes before becoming feces.
   • Oesophagus: connects mouth to stomach.
   • Anus: faeces exit.
   • Rectum: stores faeces.
   • Stomach: mixes food and drink with acid.
   • Small intestine: nutrient absorption.
   • Mouth: begins mechanical and chemical digestion.

Teaching Resources

• BBC Bitesize offers many free resources, including biology clips and resources for teachers.