The alimentary canal and peristalsis

Structure and functions in living organisms · Human nutrition · note 3 of 6

Spec 2.27, 2.28Download all Human nutrition notes (PDF)Download all notes (PDF)8 pages

The alimentary canal and peristalsisSpec 2.27, 2.28

In short

The alimentary canal is the tube from the mouth to the anus, made up of the mouth, oesophagus, stomach, small intestine (duodenum and ileum) and large intestine (colon and rectum). Food is moved along by peristalsis: waves of contraction of the circular and longitudinal muscles in the gut wall squeeze the food forward.

The alimentary canal is the tube that runs from the mouth to the anus. Food is digested and absorbed as it moves through. The liver, gall bladder and pancreas are not part of the tube, but they help with digestion.

Structure and function of the alimentary canal
Part	Function
Mouth	Teeth chew food into smaller pieces. Saliva contains amylase, which starts the digestion of starch.
Oesophagus	Carries food from the mouth to the stomach by peristalsis
Stomach	Churns food with acidic juice. Hydrochloric acid kills many bacteria. Protease digests protein.
Small intestine: duodenum	First part. Receives bile and pancreatic juice. Digestion continues here.
Small intestine: ileum	Second, longest part. Digestion is finished and the small soluble molecules are absorbed into the blood.
Pancreas	Makes digestive enzymes (amylase, protease and lipase) and releases them into the duodenum
Large intestine: colon	Absorbs water from the remaining material
Large intestine: rectum	Stores faeces, which leave the body through the anus

Front view of the human alimentary canal labelled salivary gland, mouth, oesophagus, liver, gall bladder, stomach, pancreas, duodenum and ileum (small intestine), and colon, rectum and anus (large intestine). — The alimentary canal runs from mouth to anus. The liver, gall bladder and pancreas are not part of the tube but help with digestion.

Peristalsis

Food is moved along the gut by peristalsis. The walls of the gut contain circular muscles and longitudinal muscles. Waves of muscle contraction pass along the gut.

The circular muscles behind the food contract. This squeezes the food forward.
The circular muscles in front of the food relax and the longitudinal muscles contract. This widens the tube ahead of the food.
The wave of contraction moves along the gut, pushing the food towards the stomach, then through the intestines.

Peristalsis: circular muscle contracts behind the bolus, squeezing it forward into the wider section in front.

Common mistake:

Peristalsis is a wave of muscle contraction that pushes food along. It does not break food down chemically, and it is not the same as chewing.

Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026

Frequently asked questions

What enzymes digest carbohydrates?

Amylase and maltase digest carbohydrates. Amylase, made in the salivary glands and the pancreas, breaks starch down into the sugar maltose. Maltase, made in the small intestine, then breaks maltose down into glucose. Glucose is small and soluble, so it can be absorbed into the blood in the small intestine and used in respiration.

What enzymes break down proteins?

Proteases break down proteins into amino acids. Proteases are made in the stomach, the pancreas and the small intestine. Pepsin is a protease in the acidic stomach and works best at about pH 2. The amino acids are absorbed into the blood and used to make new proteins for growth and repair.

What enzymes does the pancreas produce?

The pancreas produces amylase, protease and lipase and releases them into the duodenum. Amylase breaks starch into maltose, protease breaks proteins into amino acids, and lipase breaks lipids into fatty acids and glycerol. The pancreas is not part of the alimentary canal itself, but it helps with digestion.

All 5 questions on Human nutrition