<P> The GI tract releases hormones from enzymes to help regulate the digestive process . These hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution . </P> <P> The structure and function can be described both as gross anatomy and as microscopic anatomy or histology . The tract itself is divided into upper and lower tracts, and the intestines small and large parts . </P> <P> The upper gastrointestinal tract consists of the buccal cavity, pharynx, esophagus, stomach, and duodenum . The exact demarcation between the upper and lower tracts is the suspensory muscle of the duodenum . This delineates 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 upon function, location, and internal anatomy . The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descending, horizontal, and ascending . The suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm . </P> <P> The suspensory muscle is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively . This is a thin muscle which is derived from the embryonic mesoderm . </P>

Is the pharynx part of the gastrointestinal tract