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Human nutrition, digestion and health

The structure of the human digestive system

The structure of the human digestive system

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Explainer Video

Tutor: Safiya

Summary

The structure of the human digestive system

In a nutshell

Food travels through the digestive system so that it can be broken down into small usable molecules that can be absorbed. There are eight parts of the alimentary canal you need to know about.



The alimentary canal

The alimentary canal is a continuous pathway that starts with the mouth and ends with the anus. Food and fluid travel through it in the process of digestion. There are eight parts of the alimentary canal and five accessory organs involved with digestion.



Parts of the digestive system

​There are eight parts of the alimentary canal and five accessory organs involved with digestion.


Part of the digestive system

Explanation

Mouth and salivary glands

Food is broken down mechanically using teeth. Food is mixed with saliva made in the salivary glands. Amylase is an enzyme found in saliva which starts the chemical breakdown of carbohydrates.

Oesophagus

The oesophagus is a muscular tube connected to the mouth which squeezes swallowed food down into the stomach.

Stomach

The stomach mixes food with hydrochloric acid which destroys harmful bacteria and reduces the pH in the stomach to improve enzyme performance. Enzymes called proteases break down proteins. The muscles in the stomach churn chyme and increase exposure to enzymes.

Liver and gallbladder
The liver makes a substance called bile which is stored in the gallbladder and then secreted into the small intestine to break down large fat molecules into smaller droplets in a process called emulsification. 
Pancreas
The pancreas makes enzymes which are secreted into the small intestine.

Examples
  • Proteases which digest protein.
  • Lipases which digest lipids.
  • Carbohydrases which digest carbohydrates.

Small intestine

The small intestine is a narrow tube that makes enzymes and has special cells that absorb nutrients from chyme and transport them into the blood. 

Large intestine

The large intestine is a wider tube that absorbs water from chyme making the waste left behind thicker.

Rectum and anus
The rectum stores waste which is pushed out of the anus as poo.
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Animal nutrition and healthy eating

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Animal nutrition and healthy eating

The human digestive system

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The human digestive system

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FAQs - Frequently Asked Questions

How many parts are there to the alimentary canal?

There are eight parts of the alimentary canal.

What is the alimentary canal?

The alimentary canal is a continuous pathway that starts with the mouth and ends with the anus.

What is the purpose of the liver in digestion?

The liver makes a substance called bile which is secreted into the small intestine to break down large fat molecules into smaller droplets in a process called emulsification.

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