Digestion and Nutrition

Food, enzymes and digestive organs

What we will learn....

  • Describe the organs of the human digestive system and explain their function
  • Identify the constituents of a balanced diet and explain the function of various nutrients
  • Explain where enzymes are produced, what they are and how they work

What does the digestive system do?

The human digestive system is used to do the following things;

Ingestion - take food into the body (happens in the mouth)

Digestion - break the food up into tiny pieces

Egestion - remove the unwanted parts of the food from the body (happens at the Anus)

What are the organs of the digestive system?

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But this is what is really looks like.....

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The Main Nutrient Groups

Carbohydrate - needed for energy

Protein - growth and repair

Fat - protect the organs, store of energy, keep the body warm

Minerals - needed to keep everything healthy.For example IRON is needed to help red blood cells carry oxygen, and CALCIUM needed for healthy bones and teeth

Vitamins - needed to keep everything healthy. For example, vitamin A is needed for healthy eyesight, vitamin C is needed for healthy skin

Fibre - this is not digested but it is important as it cleans the intestines.


Digestion is breaking down large food molecules into small food molecules so that they can be absorbed in the small intestine.

There are two types of digestion

  1. Mechanical - this is physically breaking food apart (think of teeth)
  2. Chemical - this is digestion using chemicals called enzymes


Whilst the teeth are breaking the food into smaller pieces, saliva covers the food to lubricate it so it can pass easily down the oesophagus.

Saliva also contains the enzyme AMYLASE which starts to break down starch (a really big carbohydrate).

The tongue shapes the food into a ball called a bolus so its easy to swallow.


A tube (around 10cm long) that connects the mouth with the stomach. It has muscular walls that contract to push the food down towards the stomach.

Does not produce enzymes, its job is take the bolus (ball of food) from the mouth to the stomach.


The stomach has 3 jobs to do...

  1. Convert the food from a solid form into a liquid form. Every 20 seconds muscles in the stomach wall churn the food which helps to break it down.
  2. The stomach produces strong acid (hydrochloric acid) that kills most bacteria that is present in the food, this helps to prevent food poisoning.
  3. Pepsinogen (a protease enzyme) is made in the stomach that begins to digest protein.

After around 2-4 hours the food is squirted in small amounts into the first part of the small intestine.

Small intestine

This is where most of the chemical digestion happens. Carbohydrase, protease and lipase are all present in the small intestine and break down the large food molecules into small molecules, this is so they can be absorbed.

The enzymes are not made by the small intestine, they are made by an organ called the pancreas.

The inside walls of the small intestine are covered in millions of microscopic structures called villi. When food has been digested it can be absorbed through the villi directly into the blood. Villi allow absorption to happen more quickly.

What is an Enzyme?

Enzymes are chemicals made of tiny proteins that speed up chemical reactions in the body.

They are used EVERYWHERE and all of the time, without them we could not survive because the normal chemical reactions in the body would not be quick enough.

Enzymes are used to digest the food we eat

What happens AFTER digestion?

After digestion of nutrients by enzymes has occurred the nutrients need to get to all the cells of the human body so they can be used. How does this happen? Check out the link below to find out, the important words here are:


make sure you know what they mean....

Large intestine

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Once food arrives in the large intestine almost all of the nutrients (the good stuff) have been absorbed. The leftovers are made up of undigested material, water and fibre, and will be turned into faeces.

At this point there is still a lot of water in the food which needs to be reabsorbed back into the blood, this is the main job of the large intestine.

Fibre is important because it cleans the walls of the intestines and helps keep the digestive system working smoothly.

The right conditions

Enzymes in the digestive system work best at 37 degrees celcius.

As temperature changes then enzymes begin to work slower until eventually they stop working completely.

This is why having a fever or being to cold is extremely dangerous, because it means your enzymes will stop working properly.

Which organs produce enzymes?

Mouth - saliva contains an enzyme called amylase, this is a type of carbohydrase that begins to break down starch.

Stomach - contains a type of protease that begins the digestion of protein

Small intestine - this is the main organ for digestion. The pancreas produces all types of enzymes and squirts them into the small intestine.

Different Organs for Different Jobs

I can't believe it remix ( The Digestion Song) Travis Finlay
Mouth - contains teeth to chew