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The Digestive System
Digestion breaks down large molecules into smaller molecules.

The digestive system provides an interface with the environment because food substances
enter the body through it.

Each part of the digestive system has a specific function ­ all the organs have a role in
breaking down food and…

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The Mouth
The mouth is the opening to the buccal or oral cavity and is surrounded by muscular lips
which close the mouth to retain food in the cavity.

The buccal cavity is separated from the nasal chamber by the bony hard palate and
cartilaginous soft palate.

It contains:


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The Oesophagus
The oesophagus is a tube that carries food from the mouth to the stomach.

It is made up of a thick muscular wall.

It is adapted to transport, rather than for digestion or absorption.

It carries the food down the tube using waves of muscle contractions called peristalsis.…

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The Small Intestine
The small intestine has two main parts ­ the duodenum and the ileum.

The first 30 cm of the small intestine is the duodenum.

Chyme is moved along the small intestine by peristalsis in the duodenum.

Almost all of the digestion takes place in the duodenum,…

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The Large Intestine
The large intestine absorbs water, salts and minerals.

The large intestine has a folded wall which provides a large surface area for absorption.

Most of the water that is reabsorbed comes from the secretions of many digestive glands.

The food within the large intestine therefore becomes drier…

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What is Digestion?
Digestion takes place in 2 stages:

Physical breakdown
Chemical breakdown

Physical Breakdown
If the food is large, it is broken down into small pieces by means of structures such as the

This not only makes it possible to ingest the food but also provides a large…

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Chemical Digestion
Chemical digestion breaks down large, insoluble molecules into smaller, soluble ones.

It is carried out by enzymes.

All digestive enzymes function by hydrolysis.

Hydrolysis The splitting up of molecule by adding water to the
chemical bonds that hold them together

Enzymes are specific and so it follows that…


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