Small Intestine: Function, Length & Problems
The small intestine is about as big around as a middle finger, but it is about 22 feet (6.7 meters) long.
Credit: Sebastian Kaulitzki | Shutterstock

There are two types of intestines: the small intestine, also called the small bowel, and the large intestine. The small intestine is a long, winding tube connected to the stomach. It handles most of the digestion process. 

The small intestine is only about as big around as a middle finger, according to the MUSC Digestive Disease Center. The large intestine is much wider than the small intestine, but it is also much shorter. The small intestine is the longest part of the digestive system. According to the Cleveland Clinic, the small intestine is 22 feet (6.7 meters) long, while the large intestine is only 6 feet (1.8 m) long. 

Food comes into the small intestine from the stomach. It starts out as semi-solid sludge, but bile from the liver an, enzymes from the pancreas, as well as water and mucous mix with the sludge in a process called peristalsis. The mixture is quite watery by the time it gets to the large intestine.

The small intestine is a muscular tube with three parts. The duodenum breaks down the food. The jejunum and the ileum absorb nutrients and send them into the bloodstream, according to the Cleveland Clinic. The inner lining of the small intestine is folded back and forth to increase surface area for better nutrient absorption. These folds create microscopic finger-like projections that are called villi. The small intestine does its job so well, over 95 percent of ingested carbohydrates and proteins are absorbed, according to the MUSC Digestive Disease Center.

There are many ways the small intestine can become diseased or problematic. According to the U.S. National Library of Medicine (NLM), some disorders of the small intestine are bleeding, celiac diseaseCrohn's disease, infections, intestinal cancer, intestinal obstruction and blockage, irritable bowel syndrome, ulcers, pain and bacterial overgrowth.

Cancer of the small intestine is very rare when compared to other cancers. According to the American Cancer Society (ACS), only about 9,410 people per year in the United States are diagnosed with small intestine cancer, and about 1,260 people will die of small intestine cancer. The ACS also noted that 60 percent to 70 percent of small intestine cancers are carcinoid tumors, sarcomas or lymphomas.

Gluten-free diets have been touted as a great way to improve small intestine health. However, this is only true for a small number of people that have celiac disease, an immune disease that can cause damage to the small intestine after eating gluten. According to National Institute of Diabetes and Digestive and Kidney Diseases, around one in 141 have celiac disease. 

Small bowel obstruction is the blockage of the small bowel by a mass, inflammation, a twisting of the bowel or surgical adhesion that traps a loop of bowel. “Most common symptoms include nausea, vomiting, bloating, abdominal pain, increase abdominal girth or hardness and constipation. If you have any of those symptoms you should go to the hospital,” Dr. Lisa Ganjhu, a clinical assistant professor of medicine and gastroenterologist at NYU Langone Medical, told Live Science.

Depending on the degree of the blockage, symptoms can be intermittent, subtle or even related to what we eat. “For example, if someone has a narrowing, or partial blockage, of the bowel, but has a fiber-rich diet, this could potentially worsen the partial blockage,” said Dr. Razvan Arsenescu, the division chief of Gastroenterology at the Morristown Medical Center.

Bacterial overgrowth is when excess bacteria grow in the small intestines and use nutrients the body needs. A bacterial overgrowth can lead to malnutrition, dehydration, liver problems and problems related to a deficiency in vitamins and minerals, according to the NLM.

Spastic colon, also called irritable bowel syndrome (IBS), is more than just a colon problem. It is the spontaneous contractions or loss of movement of the muscles in the small and large intestines (which is also called the colon), according to the Mayo Clinic. People with IBS can experience abdominal bloating, cramping, abdominal pain, constipation and diarrhea.

A healthy, balanced diet is one of the best ways to keep the small intestine healthy, experts say. Bowel stimulants can also be helpful. “Although a healthy, balanced diet can help ensure the bowel does not become obstructed, sometimes people need products that can stimulate their bowels muscles or regulate the fluids in bowel that can help them move,” said Arsenescu.

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