Absorption in the small intestine and colon

Human nutrition · Absorption · note 1 of 2

Spec 7.5.1, 7.5.2Download all Absorption notes (PDF)Download all notes (PDF)4 pages

Absorption in the small intestine and colonSpec 7.5.1, 7.5.2

In short

Absorption is the movement of nutrients from the intestines into the blood. Nutrients are absorbed in the small intestine, mostly in the ileum. Most water is also absorbed from the small intestine, and some is absorbed from the colon. The undigested food left is stored in the rectum as faeces and removed by egestion.

Absorption is the movement of nutrients from the intestines into the blood. The small intestine is the region where nutrients are absorbed, mostly in the ileum.

Water is also absorbed. Most water is absorbed from the small intestine, but some is also absorbed from the colon. What is left in the large intestine is the undigested food, which is stored in the rectum as faeces and removed by egestion.

Where absorption happens
Region	What is absorbed
Small intestine	Nutrients (e.g. glucose, amino acids, fatty acids and glycerol, vitamins and mineral ions) and most of the water
Colon	Some water

Exam tip:

If asked where water is absorbed, say 'mostly in the small intestine and some in the colon'. 'Colon only' loses the mark.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

How is the small intestine adapted for absorption?

Supplement The small intestine is lined with villi, and the cells on each villus have microvilli, which greatly increase the surface area for absorption. Each villus has a wall only one cell thick, so the distance is short, and a network of capillaries gives a good blood supply that carries nutrients away and keeps absorption going.

Where is water absorbed in the digestive system?

Most water is absorbed from the small intestine, and some is also absorbed from the colon. The small intestine also absorbs nutrients such as glucose, amino acids, fatty acids and glycerol, vitamins and mineral ions. In an exam, say 'mostly in the small intestine and some in the colon', not 'colon only'.

What is the function of the lacteal in a villus?

Supplement The lacteal is a lymph vessel in the centre of each villus. It absorbs fatty acids and glycerol and carries them away in the lymph. The capillaries in the villus absorb glucose and amino acids into the blood instead, and the flowing blood carries them away so absorption keeps going.