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Our inside bits where IBS happens are well-hidden, so it is worth just checking where they all are.

The stomach (the size of your fist – really quite small!) is higher up than you might imagine!

This excellent review of our insides is from the Canadian Society of Intestinal Research.

Intestinal Anatomy

To understand IBS better, a basic explanation of the gastrointestinal (GI) tract is essential. The upper part of the GI tract includes the mouth, esophagus, stomach, and duodenum. Other vital components are the liver, gallbladder, pancreas, and spleen. The lower part of the digestive tract consists of two main parts, the small bowel/intestine (about 6 metres in length), and the large bowel/intestine or colon (about 1.25 metres). The upper portion of the small bowel is the duodenum and jejunum and the lower is the ileum. The colon follows the small intestine and consists of various segments, starting at the cecum and ending in the rectum and anus. (See diagram.)

Digestion begins in the mouth with chewing and mixing with saliva. Further “food processing” is continued in the stomach; however, it is the small intestine’s principal function to absorb dietary nutrients, including proteins, carbohydrates, fats, vitamins, and minerals. Bacteria (the healthy bacteria we hear about on the ads) residing primarily in the colon aid the digestive process, while the colon extracts water. The small and large intestines work together in concert with the liver, gall bladder, and pancreas to break down complex foods and to extract the right amount of each nutrient.

The intestine has a thin inner lining, the mucosa, with a surrounding submucosa, where the blood vessels and lymph channels run. Around this is a thick muscular wall, covered by a thin membrane called the serosa. When food enters the esophagus, ring-like smooth muscle contractions intricately timed with nearby muscle relaxations in a process called peristalsis, propel food along the digestive tract. Long muscles farther along in the digestive tract contract differently, helping to mix food with the enzymes produced in the gut, whose role is to break the tiny particles of food into even smaller molecules (and there are enzymes throughout the gut, including in saliva – for more on enzymes click here), further processing and propelling meal contents and promoting the passage of waste. Although most individuals are aware of intestinal movement only through having bowel movements, movement occurs constantly and is particularly prominent after meals. Ordinarily, a meal passes through the digestive tract in 24 to 40 hours but this transit time varies greatly from person to person, often depending on dietary intake composition and quantity.
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