The Digestive System (2027/28 Exams)

The Digestive System

The digestive system has two main roles:

• Digestion: Breaking large food molecules into smaller molecules. For example, carbohydrates such as starch are broken down into smaller sugars, proteins into amino acids, and lipids into glycerol and fatty acids.
• Absorption: Moving small nutrient molecules, along with vitamins, minerals, and water, from the digestive tract into the bloodstream so they can be used around the body.

Food travels through the digestive system in a sequence. As it moves, it is broken down, useful nutrients are absorbed, and undigested material is eventually removed.

Journey Through the Digestive System

1. Mouth

   • Teeth chew food, physically breaking it into smaller pieces. This increases its surface area for enzyme action and makes it easier to swallow.
   • Salivary glands release saliva. Its water helps moisten food, while the enzyme amylase begins breaking down starch into smaller carbohydrates such as maltose.
   • Enzymes are biological catalysts: they help reactions happen faster by reducing the energy needed.

2. Oesophagus (gullet)

   • A muscular tube that carries swallowed food from the mouth to the stomach.

3. Stomach

   • Muscular walls contract to churn and mix the food.
   • The stomach produces pepsin, a protease enzyme that digests proteins.
   • It also produces hydrochloric acid, which kills bacteria and provides the acidic conditions pepsin needs to work.
   • After a few hours, the stomach pushes the food mixture into the small intestine.

4. Pancreas and gallbladder

   • The pancreas releases pancreatic juices into the small intestine. These contain digestive enzymes, including carbohydrases, proteases, and lipases.
   • Bile is made in the liver, stored in the gallbladder, and released into the small intestine.
   • Bile has two functions:
     • It neutralises stomach acid, creating a more suitable pH for digestive enzymes.
     • It emulsifies lipids, breaking large fat and oil blobs into small droplets. This increases the surface area available for enzymes to act on.

5. Small intestine

   • Most digestion takes place here. Enzymes from the pancreas and small intestine help digest carbohydrates, proteins, and lipids.
   • Digested nutrients are absorbed into the bloodstream here.

How the Small Intestine Is Adapted for Absorption

The lining of the small intestine is covered in tiny, finger-like projections called villi. These are adapted for efficient absorption because they:

• Provide a large surface area for diffusion.
• Have a single layer of surface cells, making the diffusion distance short.
• Have a good blood supply, which helps maintain a concentration gradient for absorption.
• Have smaller projections called microvilli on their cells, which further increase surface area.

1. Large intestine

   • Absorbs most of the remaining excess water from the material left after digestion.

2. Rectum and anus

   • The remaining, relatively dry waste is called faeces.
   • Faeces are stored in the rectum and removed from the body through the anus.

Speakers and Sources Featured

• Cognito educational narrator: The sole speaker, explaining the digestive system and its organs.
• Cognito website and study resources: Mentioned in the closing promotion, including questions, flashcards, exam-style questions, past papers, and progress tracking.