How the Upper GI Tract Works Basically

Most of us have only a vague idea of how the digestive system works. We know, for example, that after we put food into our mouths, chew it, and swallow it, it passes into the stomach, and what’s left after digestion is complete eventually passes out of the body in the form of a bowel movement. We might remember from high school science classes that the gastrointestinal(GI) tract, where digestion occurs, is essentially a hollow tube that begins at the mouth and ends at the anus. Although it is named after its two most prominent features, the stomach (gastro-) and the intestines, the GI tract actually consists of many more vital structures (see Figure 1-1).
Figure 1-1. Major organs of the gastrointestinal system, as well as the lungs, trachea (windpipe), and diaphragm.
Figure 1-1. Major organs of the gastrointestinal system, as well as the lungs, trachea (windpipe), and diaphragm.

Most of us also have a general idea that what we eat not only comes out the other end, but also finds its way into the rest of our bodies, nourishing bones, muscles, nerves, blood, and every other organ, tissue, and cell. The familiar expression, “You are what you eat,” is at least partly true. The food we eat gets converted in the GI tract into something that quickly becomes an intimate part of our physical being. Every cell in the body is comprised of materials that began their existence somewhere in the outside world.
Digestion is the process by which food gets broken down in the GI tract by both mechanical and chemical processes, so that nutrients can be extracted from the food, absorbed into the blood stream, and distributed throughout the body for the myriad purposes involved in keeping us alive and kicking.

Although we often take it for granted, digestion involves a highly complex and well-coordinated interaction of many different acids, enzymes, alkaline substances, hormones, and other items too numerous to mention. When these are produced and released in just the right amounts at just the right times, digestion proceeds unnoticed, in the background, perfectly. But if something upsets the balance, say a deficiency in stomach acid, it can have profound health effects that may manifest as an upset stomach or heartburn, but may extend far beyond the stomach itself.
In this post, we focus on a small but extremely important part of the digestive story that takes place in the region sometimes called the upper GI tract, which includes the mouth, esophagus, and stomach. The upper GI tract functions as a kind of staging area for the digestive system. It is here that food is broken into small, manageable pieces, softened, lubricated, and liquefied. At the same time, proteins, amino acids, minerals, and other nutrients are extracted from food and processed to make them optimally available for the subsequent steps in digestion and absorption that take place later on. Any disruption here will be felt and magnified far downstream. Like most other processes in the body, digestion can be extremely complex, but don’t get scared, we’ll try to keep it simple.

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