Bowel resection: The roles of the small and large intestine
Bowel resections can occur for a number of reasons, for example, as a result of complications due to Crohn’s disease. When only a small amount of the bowel is removed, most patients can go on leading a normal life, with a normal diet. When a significant portion of the bowel is removed or when certain areas are removed, management can become more of a challenge and will need to be finely tuned until symptoms are controlled. In the latter case, nutrition and medical intervention need to go together hand in hand and both play extremely important roles.
Nutrition management after bowel resection will largely depend on the amount of bowel resected, what parts of the bowel were removed and the integrity of the remaining bowel. It can be relatively easy to stabilise or it can be very difficult. Appropriate advice will always be provided during the hospital stay and in an outpatient clinic upon discharge.
In order to understand how a resection can affect lifestyle thereafter, we first need to know what the areas of the bowel are and what functions they each carry out. An overview is provided below.
The sections of the bowel
The duodenum measures approximately 25-30cm and it is responsible for a significant amount of nutrient absorption including iron and folate . This is the first section of the small intestine which receives partly digested food from the stomach – known as chyme. Bile salts (from the gall bladder) and pancreatic enzymes (from the pancreas) will mix with food within the duodenum – this helps to break down the food further in the initial phase of digestion. It is unusual for the duodenum to be involved in a resection .
The duodenum leads in to the jejunum which is around 200-300cm . Over 90% of nutrient absorption happens here. This is also where a lot of drugs are absorbed. The jejunum has folds along it to increase surface area and hence increase the opportunity for nutrient absorption. The jejunum also releases many hormones that play specific roles in digestion and absorption . Fortunately the bowel can still function in a relatively normal manner when the jejunum is resected, if the ileum remains intact .
The ileum is around 300-400cm . This part of the bowel has almost double the functionality of the jejunum due to its extra length and its slower motility . There is a phenomenon known as the ileum break which slows down the rate of transit and allows for more contact time between nutrients and mucosa – allowing greater nutrient absorption. The ileum absorbs bile acids which are then returned to the liver .
Once excess of 100cm of the terminal ileum is removed, normal digestive functions cannot be maintained . For example, the bile salt pool (needed for digestion and absorption of fat and fat soluble vitamins) and absorption of vitamin B12 (responsible for the production of nerve cells and red blood cells). A reduction in bile salts can therefore lead to steatorrhoea (abnormal amount of fat present in stool) and losses of fat-soluble vitamins .
The fully intact ileum is able to take on most of the roles that the jejunum would have performed. It’s extra work but it does a pretty good job! The ileum can adapt well to the resection of other areas of the bowel [1,2]. Unfortunately the ileum itself has too many unique functions that other parts of the bowel cannot perform adequately and hence resection of the ileum can cause complications .
The illeoceal valve lies between the ileum and the cecum. The illeoceal valve determines how much of the ileal contents enter the colon and at what rate . The Valve increases opportunities for absorption by slowing of the transit rate of food in to the colon. It also prevents reflux of colonic bacteria back in to the ileum from the colon .
The colon averages around 160cm . It is very good at adapting its capacity for absorption when required. Its main role is the absorption of water, sodium and chloride. Food will remain in the transverse colon for approximately 6- 8 hours and will then spend time in the descending colon for around 4 hours .
Contact us for results focused nutritional advice
This article was written by our dietitian Belinda Elwin who is a Dietitians Association of Australia member and Accredited Practicing Dietitian and Nutritionist. If you have questions about nutrition guidelines after gastrointestinal surgery, make an appointment. We‘ll provide you with a simple and effective routine targeted to your concerns. Contact us today!