Your small bowel receives partly digested food from your stomach, where it has been broken down by acid and enzymes to a more liquid consistency. The three sections of this first part of your intestine (the duodenum, jejunum and ileum) then break this food down further, until all the nutrients and minerals can be absorbed into your blood.
In the duodenum, the first part of your small bowel, enzymes from the pancreas help break down the food. Your pancreas releases digestive juices through a duct into your duodenum where is breaks down fats, proteins and carbohydrates. It also contains sodium bicarbonate which neutralises acid produced in your stomach. Read more about the pancreas and pancreas transplants.
Peristalsis and absorption
Digesting food is moved through the small bowel by peristalsis. Peristalsis is a muscular contraction which causes a wave of movement to propel food along the digestive tract.
The lining of the small bowel is not smooth, it is covered by villi - tiny hair-like fingers. Each villi is covered by even tinier microvilli, resulting in a surface area of the intestine many times larger than it would appear. The absorption of nearly all the nutrients from your food occurs across this massive surface area. Each microvillus contains a miniscule blood capillary. As the nutrients are absorbed into a microvillus, they enter its blood capillary. This is how nutrients from your food enter your blood.
Any indigestible food reaches the end of the small intestine and goes through a valve into the large intestine or lower bowel. The valve is a ring of muscle which stops the contents of the large intestine travelling back into the small intestine.
When the small bowel goes wrong
When your small bowel is not working properly it may be necessary to be fed by total parenteral nutrition (TPN). Parenteral nutrition means receiving liquid nutrition through a drip.
A small bowel transplant may be considered when the person has developed complications from TPN or is unable to tolerate this form of feeding.