The gastrointestinal tract is a tube that extends from the end of the pharynx to the anus. Its functions are the propulsion and digestion of food and the elimination of the waste products. It is divided into primary segments that are, from rostral to caudal, the esophagus, stomach, small intestine, and large intestine. The primary segments are divided into secondary segments and are, from rostral to caudal: the proximal, middle and distal parts of the esophagus; the cardia, fundus, body, and antrum or pylorus of the stomach; the duodenum (with its first, second, third, and fourth parts), jejunum and ileum of the small intestine; and the cecum, appendix, ascending, transverse, descending, sigmoid, rectum, and anal canal segments of the large intestine. The histologic junctions between the primary segments may be abrupt but those between the secondary segments are gradual transition zones. Sphincters and valves at junctions of primary segments regulate forward propulsion and prevent retrograde flow of the contents. Although the general architecture of the gastrointestinal tract is established in embryonic life, there is continued development of the layers of the wall during fetal life. Thus, the histology of the gastrointestinal tract is characterized by numerous changes in the fetal period, which are highlighted in this chapter.
KeywordsLamina Propria Anal Canal Neural Crest Cell Muscularis Propria Myenteric Plexus
The author thanks Dr. Tricia R. Bhatti from The Children’s Hospital of Philadelphia, Philadelphia, PA, for invaluable assistance in selecting microscopic slides for photography, taking photographs, and editing the manuscript.
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