The innermost layer of the alimentary canal is which?

• A. Mucosa
• B. Submucosa
• C. Serosa
• D. Muscular layer

Answer: (A)

The innermost layer lines the lumen of the alimentary canal—the mucosa. It forms the mucous membrane and consists of an epithelial lining with a supporting lamina propria and a thin layer of smooth muscle called the muscularis mucosae. This layer is where secretion and absorption occur, and it often contains glands and specialized epithelium tailored to each region (for example, different in the mouth/esophagus versus the stomach and intestines). Outside the mucosa sits the submucosa, then the muscularis externa (circulatory and longitudinal muscle layers) responsible for peristalsis, and finally the serosa (or adventitia) as the outermost covering.