In this module, you will learn:

  • the organs that make up the digestive system
  • the organs that make up the alimentary canal
  • how food is absorbed into the blood stream

Resources to help you:

  • Textbook: page 71, 72 and 73
  • Notebook: page 18, 19 and 20

The Digestive System

Credit: @Krisdog via Yayimages

The digestive system

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The food that we eat needs to be broken down into smaller molecules to be able to be used by our body. The digestive system is a collection of organs that help in the process of digestion.


The digestive system is divided into two parts:

  • The alimentary canal - this is the path the food that we eat takes.
  • Other organs that helps in the process of digestion - food do not go through these organs.

The Alimentary Canal

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The alimentary canal is a series of organs that is hollow and provide a pathway for food to enter starting with the mouth and end up leaving via the anus.

Food passes through the:

Mouth ➡️ Oesophagus ➡️ Stomach➡️ Small Intestine ➡️ Large Intestine ➡️ Rectum ➡️ Anus


The alimentary canal is also known as the Gastrointestinal (G.I.) tract.

The Mouth

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A lot happens when we put food into our mouth. When we put food in our mouth, our salivary glands start producing saliva which contains the enzyme salivary amylase which is a carbohydrase. This enzyme will break down starch (a carbohydrate) into simple sugars such as maltose.


As we chew our food (mastication), the large pieces of food are broken down into smaller pieces. With the help of the tongue, the food is coated with saliva. This helps makes it easier to swallow our food.

Food enters our body through the mouth

Credit:  @MoJoeMoJo via Twenty20

Food is pushed down the oesophagus using peristalsis

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Oesophagus and Peristalsis

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Before reaching the stomach, the food we swallow will go through the oesophagus. To move food down, the muscles in the walls of the oesophagus contracts and relax in a wave-like pattern called peristalsis.

The Stomach

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The food then move from the oesophagus to the stomach where it is ready to digest proteins.

In the stomach, there's gastric juices which contains gastric acids which helps to kill microorganisms and proteases that is an enzyme that digest proteins.

The stomach is also a muscular organ and mixes food with the gastric juices through a process called churning.

Source: https://www.youtube.com/watch?v=ZuJzYYIS9c4

Digestion in the small intestine

Source: https://www.youtube.com/watch?v=5fbuJ4a-R1w

The Small Intestine

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The small intestine is the longest part of the digestive system with a length of about 7 metres.

It performs two important functions.

  1. The small intestine completes the digestion of food including carbohydrates, proteins and fats.
  2. The digested food is absorb into the blood via the villi by a process called absorption.

The pancreas produces pancreatic juice that contains all three enzymes, carbohydrase, protease and lipase. This pancreatic juice is secreted into the duodenum (small intestine).

The bile stored in the gall bladder is also released into the duodenum. Bile is secreted by the liver. It is important in the digestion of fats.

The Large Intestine

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The large intestine is where all the undigested food along with fibre, water, minerals and vitamins end up. As they move along the large intestine, water, minerals and vitamins are absorbed.

The rest of the undigested food and fibre is stored in the rectum until it is excreted as faeces through the anus.

Source: https://www.youtube.com/watch?v=ZBZWgrfZFbU

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