Digestive System Anatomy for Hepatitis Patients

The digestive system is composed of organs that work together in order to convert food, supplying basic nutrients needed by the body, into energy. Essentially, the digestive system is a long tube that’s open on either end. Food enters at one end, then passes through a long tube inside the body called the gastrointestinal (GI) tract, along which nutrients the body can use are absorbed. The residue that is not used by the body is excreted from the other end. The digestive system, which includes the liver, involves important and complicated processes essential to the body’s absorption of nutrients—beginning with the ingestion of food.

Once food has been ingested, the GI tract transports the ingested nutrients, secretes fluids and enzymes needed for digestion, absorbs nutrients from the digested products and eliminates the indigestible remains as waste.  In order to better understand how each organ in the GI tract works together and how other organs from different systems of the body work with each other, it is imperative for hepatitis patients to understand where the GI tract first starts — the mouth.

Man Eating Cheeseburger On Street
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Gastrointestinal Tract

The gastrointestinal tract is the hollow muscular tube through which ingested food and nutrients pass as they traverse the digestive system. It functions as a gateway for food as it enters the mouth and a pathway as it careens through the pharynx and esophagus. The GI tract also serves as a reservoir as chewed and swallowed food is further digested in the stomach before it is absorbed by the body as nutrients that are then taken to the other anatomical structures to be broken down further and distributed. Lastly, it acts as a “waste disposal system” as non-absorbed materials are excreted at the bottom of the tube through the anus.

All these functions are not completed via the GI tract alone. Digestive enzymes, saliva from the salivary gland, as well as products from the pancreas, liver, gallbladder, and other organs help digest food and transport nutrients. Each organ is activated or controlled by a variety of hormones. Hence, the digestive system is connected and related to the other systems of the body. For example, the circulatory system transports nutrients from the intestines to the liver for processing and then throughout the body. The nervous system helps control the release of digestive enzymes and the muscular contraction of the digestive system. These muscles provide motility in order to digest and move food and nutrients through the GI tract. The hormones and the enteric nervous system’s autonomic nerves police the activity of the GI tract.

Where Things Get Rolling in the Upper GI Tract

The “top” open end of the digestive system is the mouth. The teeth are charged with chewing and tearing food apart into smaller bits. Saliva, which is a mucous substance, is secreted and lubricates everything to kick off the dissolving process. Saliva is composed of enzymes that start the digestion of carbohydrates and fats. Saliva serves as an “adhesive,” as it holds food together en route to the stomach. The chewed food fastened with saliva is turned into a ball-piece called a bolus that is transported towards the esophagus. There are involuntary muscles in the esophagus that contract and propel food into the stomach.

Before entering the esophagus, food moves from the mouth to the pharynx. The pharynx, or throat, acts a filtering ingress into the esophagus. Aside from food passage to the esophagus, the pharynx also carries air to the larynx (voicebox) and windpipe. Connecting the pharynx to the stomach, the esophagus is a hollow conduit that has a muscular wall that propels food via the rhythmic movement of muscles that contract involuntarily. This process is known as peristalsis. In the event of peristaltic contraction when the bolus has been swallowed, smooth muscles behind the bolus are contracting so that it would not cram back to the mouth. There is a rhythmic wave that will rapidly force the bolus to be a push toward the stomach. The process of peristalsis is a one-direction movement only, to propel and keep the food moving downwards to the stomach.

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By Naheed Ali, MD
Naheed Ali, MD, PhD, is the author of "Understanding Hepatitis: An Introduction for Patients and Caregivers."