Peutz-Jeghers syndrome, named after Dr. Jan Peutz, who first described it, and Dr. Harold Joseph Jeghers, who later reported on it, is a rare autosomal dominant condition in which individuals develop polyps throughout their gastrointestinal tract, as well as dark spots called melanotic macules in their mouth, lips, genitalia, palms, and soles.
The large intestine is found in the abdominal cavity, which can be thought of as having two spaces - the intraperitoneal space and the retroperitoneal space.
The intraperitoneal space contains the first part of the duodenum, all of the small intestines, the transverse colon, sigmoid colon, and the rectum; the retroperitoneal space contains the distal duodenum, ascending colon, descending colon, and anal canal.
So the large intestines essentially weave back and forth between the intraperitoneal and retroperitoneal spaces.
Now, the walls of the gastrointestinal tract are composed of four layers.
The outermost layer is the called serosa for the intraperitoneal parts, and the adventitia for the retroperitoneal parts.
Next is the muscular layer, which contracts to move food through the bowel.
After that is the submucosa, which consists of a dense layer of tissue that contains blood vessels, lymphatics, and nerves.