Question

Which sequence below represents the correct order of the tunics of the GI tract, starting from the layer adjacent to the lumen and moving superficially?

A. submucosa, mucosa, muscularis externa, serosa
B. mucosa, submucosa, muscularis externa, serosa
C. serosa, mucosa, muscularis externa, submucosa
D. mucosa, muscularis externa, submucosa, serosa
E. muscularis externa, serosa, submucosa, mucosa

Answer 1

The correct order of the tunics of the GI tract, starting from the layer adjacent to the lumen and moving superficially, is mucosa, submucosa, muscularis externa, and serosa.

Step-by-step explanation:

The correct order of the tunics of the GI tract, starting from the layer adjacent to the lumen and moving superficially, is as follows:

1. Mucosa: The innermost layer surrounding the lumen. Consists mainly of the epithelium with the capacity to secrete and absorb substances.
2. Submucosa: Lies immediately beneath the mucosa. A broad layer of dense connective tissue that connects the mucosa to the muscularis. Contains blood and lymphatic vessels, submucosal glands, and a network of nerves called the submucosal plexus.
3. Muscularis externa: Also called the muscularis. The third layer of the alimentary canal. Consists of circular and longitudinal smooth muscle fibers that help move food through the GI tract.
4. Serosa: The outermost layer of the walls of GI tract organs. A thin layer of connective tissue that separates the organs from surrounding tissues and cavities.