Bowel obstruction is when the normal flow of contents moving through the intestines is interrupted.
The causes of bowel obstruction can be either mechanical or functional, also called ileus.
Mechanical obstruction is caused by actual blockages in the large or small intestine, and it can be defined as partial or complete.
Partial obstruction is when gas or liquid stool can pass through the point of narrowing, while complete obstruction is when nothing can pass.
Functional causes disrupt peristalsis, which are the waves of contraction that move through the smooth muscles of the bowel wall that pushes food through the intestines.
The small and large intestines are tube-shaped structures through which chyme, or food that has been partly digested by the stomach, and stools pass until they’re excreted.
Now if we zoom into a cross-section of the intestinal wall, it’s lined by four layers of tissue: First, there’s the adventitia, or serosa; which is the outermost layer that faces the abdominal or peritoneal cavity. This is the space between the abdominal wall and the abdominal organs, and it’s lined by peritoneal membranes that contains a thin film of serous fluid.
Moving on, there’s the muscularis externa, which is smooth muscle that contract to move food through the bowel.
Deep beneath this layer is the submucosa, which has connective tissue as well as glands, blood and lymph vessels that supply the intestinal wall.
And finally, the innermost layer is the mucosa and it’s composed of a few of its own layers: the muscularis mucosae, which has smooth muscle, the lamina propria, which is rich with blood and lymph vessels, and the innermost layer which is the epithelial lining that faces the lumen.