(or gullet) is a tube that transports food, once it is swallowed, from the mouth to the stomach. A valve at the bottom of the esophagus prevents food and stomach acid from coming back up into the esophagus and into the mouth, where it can cause heartburn, which can result in damage to the inner lining of the esophagus. When you vomit, this valve opens up to allow acid and food to come out, and when you burp, it opens to allow gas to come out.
IBD Ulcers
An area that has lost its mucosal lining is called an ulcer. When people talk about ulcers, they are usually referring to duodenal or gastric (stomach) ulcers, which are typically different from the ulcers that may occur in inflammatory bowel disease. In Crohn’s disease and ulcerative colitis, the ulcers usually occur in the small intestine and large intestine and much less commonly in the stomach and duodenum.
Stomach
This saclike structure lies in the upper part of the abdomen. It receives and holds food that has recently been eaten and slowly pushes it down into the small intestine, where most of the absorption of nutrients occurs. There is a valve at the lower end of the stomach that helps to regulate how quickly the food leaves the stomach to enter the small intestine. The stomach provides an important signal to the brain to indicate when you have eaten enough.
The stomach also secretes acid from its lining. This helps to protect against infections caused by harmful bacteria that might inadvertently be ingested during a meal. The stomach acid also helps with the initial digestion of proteins in food. An enzyme called pepsin, also produced by the stomach, provides additional help with breaking down proteins.
Small Intestine
The small intestine (or small bowel) is a tubular structure approximately 12 to 15 feet (4 to 5 m) long. It is divided into three segments: from top to bottom, these are the duodenum, the jejunum, and the ileum. In the small intestine, most of the nutrients in food are absorbed into the body.
Mucosa
The absorption of nutrients is dependent upon the presence of a highly specialized inner lining (or mucosa). The mucosa lining is made up of cells whose main reason for being is to absorb nutrients from the inside (or lumen) of the intestine and pass them through into the body, where they are available as building blocks or fuel for other body functions. The surface of the mucosa is folded into many tiny fingerlike projections, called villi, which effectively increase the surface area and, therefore, the number of cells available for absorption of nutrients.
The surface of these cells contains enzymes that help break down food into smaller components so as to be absorbed more easily. When the intestine is inflamed, as is the case in inflammatory bowel disease, the villi may be reduced in number or size — or may be wiped out altogether so that the inner lining of the intestine appears flat. This loss of normal villi results in a reduced ability to absorb nutrients. When the inflammation is severe, the mucosa lining may be completely gone, leaving the underlying tissue exposed to the inside of the intestine.
Large Intestine
The large intestine, also known as the colon, is approximately 3 to 4 feet (1 to 1.2 m) in length. Although shorter than the small intestine, it is called the large intestine because its width or diameter is greater than that of the small intestine. It is divided into several sections: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.
Primary Function
The large intestine’s primary function is to absorb fluid (water) and minerals, such as sodium and potassium, from the intestinal contents back into the tissues and into the bloodstream. By absorbing fluid, the colon causes the stool to be solid rather than liquid and helps to prevent fluid loss and dehydration.
Small Intestine
Rectum
The last part of the large intestine is called the rectum. The wall of the rectum can stretch, up to a certain point, to allow stool to be kept inside until there is an appropriate time to evacuate. When the rectum is inflamed or somehow diseased in other ways, that ability to hold stool is reduced, and you may feel the need to go to the bathroom very frequently and urgently. In some instances, this can result in accidents with associated loss of control of bowel function, otherwise known as fecal incontinence. This need for frequent bathroom visits and the urgency that may go along with it can be one of the most troubling symptoms of inflammatory bowel disease.
Related Parts of the Gastrointestinal Tract
There are other parts of the gastrointestinal tract involved to a greater or lesser extent in digestion and nutrient absorption. These organs, which are typically connected to the tubular part of the gastrointestinal tract by small channels (or ducts), include the liver, gallbladder, and pancreas. The gallbladder and pancreas are usually not affected by inflammatory bowel disease. However, the liver may be affected in a small proportion of patients. Occasionally, this can lead to liver damage.
Liver
The liver has many functions, but the one that is most involved in digestion is bile production. Bile is similar to a detergent, in that it allows fat to be broken down and made into a form that can be dissolved or mixed with water. Normally, fat remains separate from water, like the fat floating on the top of chicken soup. This ability of bile to break up fat into small particles and disperse those particles in the watery contents of the small intestine is crucial to fat digestion and absorption.
Gallbladder
Bile that is produced by the liver is usually stored in the gallbladder, a small sac next to the liver, until it is needed after a meal. When the production of bile is not adequate or if bile is blocked from reaching the intestine, absorption of fat from the diet is reduced. As a result, fat may end up coming out in the stool. This appears as droplets of fat or oil in the stool.
Pancreas
The pancreas is a gland producing a number of digestive enzymes that enter the upper part of the small intestine. The pancreas lies very close to the duodenum and has a small duct running through it that carries the enzymes from the pancreas into the duodenum. These enzymes help break down protein, starch, and fat in the diet into components that can be easily absorbed by the intestine.
Anus
The anus (or anal canal) is the passageway that stool follows when it leaves the body. The primary role of the anus is to keep the stool that is present in the rectum from coming out when you don’t want it to come out. In other words, it helps to prevent fecal incontinence. Within the anal canal, there are two main muscular anal sphincters (or valves) that help to prevent the stool from coming out involuntarily.
One of the sphincters, called the external anal sphincter, is under your conscious control. In other words, you can control or tighten this particular sphincter when trying to hold in stool or gas. The other sphincter, the internal anal sphincter, is not under voluntary control, but works reflexively at a subconscious level. Maintaining continence and ensuring the smooth and complete emptying of the rectum requires the coordination of the two anal sphincters. If either of these two sphincters is
