Final answer:
The serosa of the GI tract is the outermost layer composed of visceral peritoneum and loose connective tissue, present in the abdominal cavity.
Step-by-step explanation:
The serosa of the wall of the gastrointestinal (GI) tract is composed of a layer of visceral peritoneum overlying a layer of loose connective tissue. This serosa layer is the outermost layer of the walls of GI tract organs within the abdominal cavity, separating these organs from surrounding cavities and tissues.
The serosa layer is continuous with the mesentery, which helps to hold the organs in place and is part of the broader peritoneum that includes both the parietal peritoneum lining the abdominal wall and the visceral peritoneum covering the abdominal organs. In the regions of the alimentary canal that are not within the abdominal cavity, such as the mouth, pharynx, and esophagus, there is instead a dense sheath of collagen fibers called the adventitia.