|
|
|
What is GIST?
GIST stands for Gastrointestinal Stromal Tumor.
|
|
The Gastrointestinal System
The gastrointestinal system is part of the digestive system, which is responsible for breaking down food and providing nutrition to
the body (Picture 1). It starts with the mouth, where foods gets bitten and chomped into small bits. It then travels down
the esophagus into the stomach. There, it meets a very harsh, acidic environment, that breaks down the small bits of food even further
into microscopic particles, resulting in the core nutrients of food: fat, protein and sugar. The highly digested particles are then
propelled into the small intestine, where they are now in a form small enough that they can be transported through the walls of the
intestines and into the blood stream. This allows the nutrients to get distributed to the parts of the body that require them the
most. Back in the small intestine, what remains then gets propelled further into the large intestine, also known as the colon, where
water get absorbed. What ever is left over gets propelled into the rectum, where the remains are stored, until expelled. It is
remarkable to think that something as solid as an apple can be minced down into such small particles that it can enter the blood
stream and supply nutrition to the body as needed.
The Stroma
The official definition of stroma is “A supportive framework of an organ usually composed of connective tissue.” This definition is
probably not that clear, so we will provide a comparison of the stroma to something that everyone is familiar with, a house. There
are rooms in your house that are designed for certain functions, like the kitchen and the living room. Both of these rooms serve very
different purposes and they require different elements to make them functional. Now imagine the rooms without any walls and you would
see all of the important items that make the rooms functional, including electrical wiring, water pipes, insulation and support beams.
|
|
|
|
To continue the analogy, we will concentrate on the kitchen. The kitchen is used to prepare food. In order to do this,
there are certain appliances that are required, such as a refrigerator and a sink. But these items would not function without the elements
that are behind the walls, such as electrical lines and water pipes. Just as importantly, without the framework of
the house, the beams and the insulation, there would be no support structure for these important lines to get to the items that they
serve. The supporting framework of the kitchen is composed of wood beams and insulation, through which run all the electrical lines
and water pipes, that allow the kitchen to function. Similarly, the supporting framework (stroma) of the stomach is composed of
connective tissue, through which run the nerves and blood vessels, that allow the stomach to function.
|
|
The Tumor
A tumor is any abnormal growth in the body.
|
|
Layers of the Stomach
There are six layers that make up the stomach (Picture 2). The inner most layer is the mucosa. It is composed of three main types
of cells. Chief cells and parietal cells release harsh acids into the stomach, breaking down the food into smaller particles.
Epithelial cells make up the vast majority of the mucosa. Their purpose it to form an impenetrable barrier, so that the harsh acidic
environment of the stomach cannot penetrate and harm the rest of the body. The epithelial cells in the mucosa can be thought of as
the walls of the kitchen. Of note, most adult cancers result from malignant changes in epithelial cells and are termed carcinomas,
such as stomach cancer (gastric carcinoma) and colon and rectal cancer (colorectal carcinoma). This is marked contrast to GIST.
The second and fourth layers of the stomach are called the muscularis mucosa and the muscle layer. These layers are composed of
muscles that help propel the food from the stomach into the small intestine.
|
|
|
|
|
The fifth and sixth layers are the subserosa and the serosa, both of which provide cover for the stomach.
The third layer is the submucosa. It is composed mostly of connective tissue and it in this layer that the nerves and blood vessels
are located. Also located here are the Interstitial Cells of Cajal. These are pacemaker cells of the gastrointestinal tract,
forcing muscles to squeeze, thus propelling food particles along from the stomach into the small intestine and then into the
large intestine. It is thought that unwanted changes in Interstitial Cells of Cajal give rise to GIST. Unlike epithelial cells which are derived
from
a superficial layer, cells in the submucosa are derived from a middle layer called the mesenchyme, and
therefore GIST tumors are referred to as sarcomas, and not carcinomas.
Looking again at the layers of the stomach (Picture 2), due to the central location of the submucosal layer, tumors can grow inward,
penetrating the lining of the stomach and causing bleeding into the gastrointestinal tract. In addition, tumors can also grow outward. In these cases, there may be no
symptoms early on, with the possible exception of pain. Although the vast majority of younger patients with GIST have stomach tumors,
some patients may have tumors that develop in the intestines. In both organs, the layers are similar and they both contain Interstitial Cells of Cajal.
|