Editing Gastrointestinal tract (section)

====Upper gastrointestinal tract====
{{Main|Mouth|Pharynx|Esophagus|Stomach|duodenum}}
The upper gastrointestinal tract consists of the [[Human mouth|mouth]], [[pharynx]], [[esophagus]], [[stomach]], and [[duodenum]].<ref>{{MeSH name|Upper+Gastrointestinal+Tract}}</ref>
The exact demarcation between the upper and lower tracts is the [[suspensory muscle of the duodenum]]. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe [[gastrointestinal bleeding]] as being of either "upper" or "lower" origin. Upon [[dissection]], the duodenum may appear to be a unified organ, but it is divided into four segments based on function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): [[duodenal bulb|bulb]], descending, horizontal, and ascending. 

The suspensory muscle of the duodenum suspends the superior border of the ascending duodenum from the [[thoracic diaphragm|diaphragm]], and serves as an important anatomical landmark showing the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively.<ref name="Warrell2005">{{cite book|author=David A. Warrell|title=Oxford textbook of medicine: Sections 18-33|url=https://books.google.com/books?id=hL1NKQJlY1IC&pg=PA511|access-date=1 July 2010|year=2005|publisher=Oxford University Press|isbn=978-0-19-856978-7|pages=511–}}</ref> This is a thin muscle which is derived from the [[embryo]]nic [[mesoderm]].