Endoscopic Anatomy Of The Gastrointestinal Tract

Abstract

The present study dealt with the endoscopic anatomy of the gastrointestinal tract (GIT). A note on the history of the development of the endoscopes was given. In that respect, Philip Bozzini in 1805 invented the first endoscope called Lichtleiter. In 1873, Trouvé was the first to use internal illumination in the endoscope. Then, Schindler succeeded to invent the flexible endoscope in 1932. In 1957, Hirschowitz developed the fiberoptic endoscopes. There are two main categories of endoscopy, rigid and flexible. In each type the endoscope is named after the body part being viewed. The gastrointestinal endoscopes include the upper gastrointestinal endoscope "Gastroscope"; which can examine the oesophagus, stomach and part of the duodenum, and the lower gastrointestinal endoscope "Colonoscope"; which can examine the anal canal, rectum, sigmoid colon, descending colon, transverse colon, ascending colon, caecum and terminal part of ileum. In the present study, the normal anatomy of the gastrointestinal tract was discussed both in the conventional way and by the endoscope. Endoscopy, is mainly concerned with observing the difference in the mucosal lining of the different parts of the GIT. Correlation between conventional and endoscopic anatomy helped to understand the impact of the surrounding structures on the changes seen within the lumen of the GIT both in health and disease. The present work demonstrated the difference in the mucosal lining of the upper GIT as seen by the Gastroscope. The mucosal lining of the oesophagus characterized by its pearly white or pinkish-grey color changed into salmon colored mucosa of the stomach. The transition between oesophagus and stomach usually forms a zig-zag (Z) line where projections of the gastric columnar epithelium that extend up to 5 mm cephalad along the margin of the oesophageal squamous mucosa, this is called squamo-columnar junction (SCJ) . Moreover, as the endoscope enters the cardiac end of the stomach, the mucosal folds of the stomach "Rugae" starts to appear. On the other hand, endoscopy of the lower GIT revealed that the lining of anal canal is divided into upper mucosal (endoderm) and a lower cutaneous (ectoderm) segment, the junction between these two areas called " Dentate line". The 0.5- to 1.0-cm strip of mucosa above the dentate line presents, 8–14 longitudinal folds, known as the anal columns (columns of Morgagni). The cutaneous part of the anal canal consists of modified stratified squamous epithelium that is thin, smooth, pale, stretched, and devoid of hair and glands. The mucosa in the area of the columns consists of several layers of cuboidal cells and has a deep purple color because of the underlying internal hemorrhoidal plexus. Cephalad to this area, the epithelium changes to a single layer of columnar cells and acquires the characteristic pink color of the rectal mucosa which is thick, darker and somewhat more highly vascularized than any other mucosa in the gastro-intestinal tract. The rectum, contains three semicircular valves or transverse folds of the rectum called " valves of Houston". All parts of the large intestine proximal to the rectum has the same characteristic mucosa which is shiny, smooth and the blood vessels are clearly visible. In addition, these parts of the large intestine have numerous folds " Haustrations" and according to the thickness of these folds there are gradual changes in the shape of the lumen of the different parts of the large intestine. The lumen shape changes from rounded or oval in the sigmoid colon into oval or triangular in the descending colon then to triangular in the transverse colon and the ascending colon. Furthermore, the mucosal lining of both the left and right colic flexures frequently shows a bluish coloration as a reflection from the spleen and the liver, respectively. Only, 10–15 cm of the terminal ileum can usually be viewed. The caliber of the terminal ileum is significantly smaller than that of the colon. The transverse folds typical of the small proximal intestine are less pronounced in the terminal ileum or lacking completely. The mucosa is distinctly different from the colonic mucosa, by being velvety and granular. The present work discussed the endoscopic picture of the most common diseases of the GIT in correlation with the normal endoscopic anatomy and the ability of the endoscope to be the primary diagnostic tool in the diseases of the GIT. These diseases included diverticulosis, some tumours and inflammatory diseases. In diverticulosis, the endoscopy revealed which are fingerlike outpouchings protruding outward from the intestinal lumen. Benign tumours may take the from of polyps protruding into the lumen of the bowel and have different types according to their appearance, they may be stalked, round or sessile masses of variable sizes. Malignant tumours are the most common tumors in the GIT and the most common form is adenocarcinoma and there is a special precancerous lesion in the oesophagus called " Barrett's oesophagus". Regarding the inflammatory diseases, the endoscopic picture of oesphagitis varied in severity from some erosions to severe haemorrhagic ulcerations. In gastritis, patchy or more diffuse red discoloration contrasting with the normal pink color of the adjacent mucosa, could be identified. Colitis may reveal the presence of multiple ulcers with acute or chronic bleeding.