Discover how the GI tract works to understand how SBS can affect it
The digestive system
The human digestive system is made up of several organs that help the body break down and absorb the nutrients it needs to function. The key players are the stomach, small intestine and large intestine, which work together to process the food and water you eat and drink into nutrients your body can use.
To learn more about how the normal GI tract works to absorb nutrients and fluid, talk to your doctor and sign up to receive a copy of A Patient’s Guide to Managing a Short Bowel by Carol Rees Parrish, MS, RD.
The image below is for illustrative purposes and is not an exact model of the human body.
After you chew and swallow your food, it travels down the esophagus into the stomach. Once there, your body starts releasing enzymes and bile to help break down the food. Here in the stomach, the food is broken down into partially digested food called chyme. The chyme then moves on to the next phase of digestion in the small intestine.
The small intestine AND villi
Once your food has been initially broken down in the stomach into chyme, it passes into the small intestine, or small bowel, where it’s broken down even further. The normal length of the entire small intestine is approximately 12 to 20 feet, but many SBS patients have less than seven feet.
The interior surface of the small intestine is covered with microscopic intestinal villi.
As chyme moves through the intestine, tiny pieces of nutrients attach to these intestinal villi. This makes them very important to the digestion process as they help maximize the surface area of the organ, directly absorb nutrients and allow them to enter into your bloodstream.
The small intestine is made up of three different segments: the duodenum, the jejunum and the ileum. Though there is no physical barrier between them, each section is subtly different and performs a different role in absorbing nutrients from the chyme as it passes through the system.
The duodenum is a short tube at the beginning of the small intestine that receives the chyme, enzymes and bile from the stomach. The duodenum absorbs fats, sugars, peptides/amino acids, iron, folate, calcium, water, magnesium and electrolytes.
The jejunum is the middle section of the small intestine. It connects the duodenum and the ileum and absorbs sugars, calcium, peptides/amino acids, electrolytes, magnesium and water.
The ileum is the last section of the small intestine and connects it to the large intestine. It absorbs the water, bile acids, electrolytes and vitamin B12 that were not absorbed by the jejunum. The terminal ileum also secretes several hormones that are thought to influence appetite, intestinal motility and intestinal absorption.
The large intestine
The terminal ileum is immediately followed by the ileocecal valve, which connects the small intestine to the large intestine and prevents bacteria from the large intestine from working its way into the small intestine. It also holds the chyme in the small bowel, which helps give it more time to absorb nutrients.
After the small intestine has absorbed nutrients from the chyme, the remaining chyme moves into the large intestine, or colon. It begins removing water from the chyme and prepares the remaining waste material for disposal.
The first part of the large intestine is the cecum which forms a pouch and connects to the ascending colon. The muscles of the ascending colon push the chyme upward. This allows the system to absorb water. This process takes about eight hours for a healthy person with normal anatomy.
The transverse colon is the middle segment of the colon. It continues to absorb water as chyme travels across this segment for the next six to eight hours.
Then comes the descending colon. Here, chyme is made more solid and prepared for elimination. This process takes about four hours.
The sigmoid colon connects the descending colon to the rectum and stores the waste until it’s ready to be eliminated.
SBS and the digestive system
If you have SBS, you might be unable to absorb the necessary nutrients and fluids you need from your diet. That’s probably because you’re missing pieces of your intestinal tract. Label the digestive system worksheet to visualize your own digestive system. If you don’t know what section or length of your bowel has been removed, your doctor or surgeon should be able to tell you.