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24 September 2014
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Organs - Small intestine

System: Digestive

Location: Abdomen

Physical description: A five metre long narrow tube that hangs in sausage-like coils

Function: Chemical digestion of food and absorption of nutrients into your blood

Longest section of your digestive tract

Your small intestine is around five metres long, making it the longest section of your digestive tract. Although it is longer than your large intestine it has a smaller diameter. This is why it's called the small intestine.

Chemical digestion

After food is churned up in your stomach, a sphincter muscle at the end of your stomach opens to squirt small amounts of food into the top of your small intestine. This first section of the small intestine is called the duodenum.

Your pancreas releases digestive juices through a duct into your duodenum. This fluid is rich in enzymes that break down fats, proteins and carbohydrates. It also contains sodium bicarbonate which neutralises acid produced in your stomach.

Your gall bladder squeezes out bile down a duct into your duodenum. Bile helps break down fats in your food.

Peristalsis

Digesting food is pushed through the small intestine by peristalsis. Peristalsis is a muscular movement in which alternating waves of muscle contraction and relaxation cause food to be squeezed along the digestive tract.

Absorbing nutrients

Most of the nutrients in the food you eat pass through the lining of your small intestine into your blood. The lining of the small intestine is covered in tiny microvilli. These are microscopic, finger-like protrusions which give the lining of the small intestine a massive surface area for absorption of nutrients to occur across. The microvilli give the inside of the intestine the look and feel of velvet.

Each microvillus contains a minute blood capillary. When nutrients are absorbed into a microvillus, they enter its blood capillary. This is how nutrients from your food enter your blood.

Indigestible food passes into the large intestine

By the time food leaves your small intestine all the nutrients in your food will have entered your bloodstream. All that remains is indigestible food which is passed from your small intestine to your large intestine for further processing.

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