![]() As these muscles contract, they propel food along the digestive tract. Outside of the submucosa is a layer of muscle, the muscularis externa. The second layer is the submucosa, which consists of a dense layer of connective tissue with blood vessels, lymphatic vessels, and nerves. ![]() In the small intestine, it is responsible for both the secretion of digestive juices and the absorption of nutrients. The mucosa is the innermost layer of the GI tract wall. Iron is absorbed in the duodenum, and vitamin B12 and bile salts are absorbed in the last part of the ileum (terminal ileum). Functions of the small intestine include secreting digestive enzymes and buffers, and absorbing nutrients. ![]() The first section of the small intestine, the duodenum, is the smallest segment, which is about the same length as the stomach (25 cm/~10″), followed by the jejunum (2.5 m/~8′) and the ileum (3.5 m/~11.5′), for a combined total of a little more than 6 m (~20′). This is where most digestion and absorption of food takes place. It has an enormous internal surface area due to the presence of millions of tiny finger-like protrusions called villi, which are covered in hair-like protrusions called microvilli. The small intestine is a long and narrow coiled tube that extends from the stomach to the large intestine, winding around within the abdomen. Small and large refer to the diameter, which for the small intestine is about 2.5-3 cm (~1″) compared to 6.5-7 cm (~2.5″) for the large intestine. The names of these parts are a bit confusing, as the small intestine is about three times as long as the large intestine. The lower part of the GI tract includes the small and large intestines. Strong chemicals break food down into smaller components, while the stomach’s thick walls keep these chemicals from entering the body as it squeezes its contents with strong circular and longitudinal muscles. ![]() It increases in diameter as it receives food, holding up to a maximum of about 4 litres (but do not eat so much as to extend the stomach fully). The composition and quantity of dietary intake, the presence of a GI disease or disorder, and other factors influence transit time.įollowing the esophagus, located within the left side of the abdominal cavity, is the stomach, a sac-like organ about 25 cm (~10″) long. Some individuals have an irregular pattern, never knowing what to expect. Each person is unique a normal bowel movement pattern for one person may be very different from those of family members or friends. A meal could take anywhere from 12-72 hours to travel through the digestive tract. Transit time is the duration between when you take a bite of your meal and when leftover waste finally passes out as stool (feces). If all is going well, the passage of food from one area of the intestines to the next is precisely coordinated, so that it stays in each area for just the right amount of time. A number of body systems provide the chemicals necessary to complete digestion, absorption, and elimination. Chewing and swallowing (ingesting) require conscious effort, but once food reaches the esophagus, an automatic, rhythmic motion (peristalsis) takes over, propelling the contents along. In the mouth, chewing mechanically breaks down and mixes food, while saliva begins to modify it chemically, thus beginning the digestive process. The upper part of the GI tract includes the mouth, throat (pharynx), esophagus, and stomach. The dimensions mentioned below are for an average adult male. The size and shape of the digestive tract varies according to the individual (e.g., age, sex, size, and disease state). The digestive system consists of a long tube (alimentary canal) that varies in shape and purpose as it winds its way through the body from the mouth to the anus (see diagram). This explanation is not complete, but it covers the basics. To understand IBD, a review of gastrointestinal (GI) tract anatomy is helpful. Inflammatory Bowel Disease Intestinal Anatomy Click here to download a PDF of this information.
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