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.

1a. Mouth, 1b. Salivary glands, 2. Oesophagus, 3. Stomach, 4a. Liver, 4b. Gallbladder, 5. Pancreas, 6. Small intestine, 7. Large intestine, 8. Rectum, 9. Anus

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.