Final answer:
The defect in the mesentery must be closed after a colon anastomosis to prevent postoperative obstruction. The mesentery supports the intestines and contains critical blood vessels and nerves.
Step-by-step explanation:
Upon completion of a colon anastomosis, the defect in the mesentery must be closed to prevent postoperative obstruction. Option (a) Mesentery is correct. The mesentery is a double layer of peritoneum that attaches parts of the intestine to the posterior abdominal wall, providing support and carrying the blood vessels, lymphatics, and nerves that supply the intestinal wall. When an anastomosis is performed, which is the surgical connection between two parts of the intestine, care must be taken to ensure that all layers, including the mesentery, are properly aligned and secured to prevent complications such as obstruction.
The serosa is the outermost layer of the alimentary canal, present in the abdominal cavity, and consists of the visceral peritoneum overlying loose connective tissue. It's important to distinguish this from the mesentery, which is specifically the focus when closing defects post-anastomosis to avoid obstructions.