The Small Bowel

The small bowel, or small intestine, absorbs minerals and nutrients from your food and is part of the digestive system. This soft, elastic tube is greatly coiled. It receives partly digested food from the stomach and passes it to the lower bowel (large intestine).

Small bowel transplant facts

An adult's small intestine (bowel) is roughly six or seven metres long - much longer than the large intestine.
About 90% of the food we eat enters the blood through the wall of the small bowel through highly specialised cells lining the wall of the bowel. Your digestive system works to break down this food into small enough particles to be absorbed.
A small bowel transplant is complicated and takes around 8 to 10 hours.

Common reasons for transplantation

Small bowel (or intestinal) transplants are not common. Serious failure of the small intestine would normally lead to receiving nutrition through a drip into your veins (total parenteral nutrition). When this method of feeding is not possible or becomes intolerable, a small bowel transplant may be considered.

The common causes of small bowel failure include diseases such as extensive and unresponsive Crohns disease and digestive disorders. The most common clinical condition to cause intestinal failure is short bowel syndrome - a disorder usually resulting from surgical removal of part of the small bowel.

How it works

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.

Small bowel transplants

A small bowel transplant is complicated and takes around 8 to 10 hours of surgery. The kind of transplant surgery chosen will depend on the cause of bowel failure. There are three main types of transplant that may be considered:

Small bowel transplant - recommended for patients with bowel failure who do not have liver disease

Combined liver and small bowel transplant - recommended for patients with bowel failure who also have end-stage liver disease

Multivisceral (multiple organ) transplant - may be recommended for patients with multiple organ failure, although it is not commonly used. The diseased stomach, pancreas, duodenum, liver and small bowel are removed and healthy donor organs transplanted

In this transplant procedure the surgeon removes the bowel and replaces it with a donated healthy organ. This new organ is connected up with your blood vessels and digestive tract.

An ileostomy is then performed. The surgeon performs the ileostomy by creating an opening through which part of the small bowel is passed through the abdominal wall. This opening allows body waste to pass directly out of the body and empty into a pouch. The ileostomy also allows the transplant team to keep an eye on the health of the patient's transplanted intestine. In time, most patients are able to have the ileostomy closed.

After the transplant operation, patients can be moved from total parenteral nutrition (TPN) to a normal diet fed through the mouth.

Transplant surgery is improving all the time. Surgeons are now able to successfully reduce an adult intestine to a fraction of its normal size so that it can be implanted in a child. In the future, it may be possible to take both a section of the liver and a section of an intestine from a living-related donor. Read more about living liver donors and living kidney donors.

History and progress of small bowel transplantation

Although experiments with intestinal transplantation were being conducted in the early 20th century, it is only relatively recently that it has become a viable clinical procedure. The small bowel has presented a difficult challenge for transplantation and rejection is still an important risk today.

The first reported human intestinal transplant was performed in 1967. Before 1970, eight clinical cases of small-intestine transplantation were reportedly performed worldwide. The best graft survival time was 79 days, and all patients died of technical complications, infections, or rejection of the transplanted organ.

In 1988, German surgeons performed what is considered to be the first successful intestinal transplant. Intestinal transplantation has evolved in the past decade from being considered an experimental procedure to what is considered today as the only long-term option for patients with intestinal failure who have developed irreversible complications associated with long-term feeding through a drip.

Advances in surgical technique, improved rejection rates and post-operative care mean that small bowel transplants now offer patients greatly improved chances of long-term survival and an enhanced quality of life.

More than 85% of patients currently survive for at least a year, which is comparable to liver transplant patients. Eighty percent of patients who have had an intestinal transplant are able to switch from being drip-fed to an oral diet and resume normal activities of daily living.

Mini Glossary

  • Duodenum (say joo-o-deen-um):
    The first section of the small bowel
  • Ileum (say ill-ee-um):
    The final section of the small bowel
  • Ileostomy:
    A surgical opening through which the end of the intestine (the ileum) is brought out onto the surface of the skin
  • Jejunum (say jay-joo-num):
    The middle section of the small bowel
  • Peristalsis:
    The contraction of muscles to propel food through the digestive system
  • Short bowel syndrome:
    A disorder in which the small intestine can not absorb sufficient nutrients
  • Total parenteral nutrition (TPN):
    Being fed liquid nutrition through a drip
  • Villi:
    Clusters of small finger-shaped outgrowths that increase the surface area of cells

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