Digestive system
Small Intestine
The small intestine is a long, coiled tube where most digestion and nutrient absorption happens. Despite its name it is around 6–7 metres long — the longest part of the digestive tract.
What it is
The small intestine is a narrow, coiled tube in three parts (duodenum, jejunum and ileum) between the stomach and the large intestine.
Where it is
Filling much of the central abdomen, coiled between the stomach and the large intestine.
What it does
Completes digestion and absorbs the vast majority of nutrients — carbohydrates, proteins, fats, vitamins and minerals — into the bloodstream.
How it works
Food from the stomach mixes with bile from the liver and enzymes from the pancreas. The inner surface is covered in millions of tiny finger-like projections (villi) that hugely increase the area for absorbing nutrients into the blood.
When things go wrong
Common conditions affecting the small intestine
- Coeliac disease
- Crohn's disease
- Malabsorption
- Bowel obstruction
Education and reference only. This explains the anatomy in plain terms and is not a diagnosis. Sudden severe symptoms — such as severe chest pain, breathlessness or collapse — are an emergency; call 999.
Looking after it
Keeping your small intestine healthy
A balanced, fibre-containing diet and prompt assessment of persistent digestive symptoms support gut health.
Did you know?
An interesting fact
The small intestine's villi give it an inner surface area of around 30 square metres — helping it absorb nutrients efficiently.
Answers
Small Intestine: frequently asked questions
What does the small intestine do?
The small intestine completes digestion and absorbs most of the nutrients from food into the bloodstream.
Why is it called "small" if it is so long?
It is "small" because it is narrower than the large intestine, not shorter — in fact it is much longer, at around 6–7 metres.
The digestive system
Related organs
Sources
Where this is drawn from
- NHS — Anatomy and body systems
- Gray's Anatomy for Students
- TeachMeAnatomy / TeachMePhysiology
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