Final answer:
The alimentary canal consists of four layers: the mucosa (innermost layer for absorption and secretion), the submucosa (contains blood vessels and nerves), the muscularis (responsible for peristalsis), and the serosa (outermost protective layer). Thus, the correct option describing the layers and their functions is A) Mucosa, Submucosa, Muscularis, Serosa.
Step-by-step explanation:
The alimentary canal is structured with four main layers known as tunics, each with distinct functions. These layers, from innermost to outermost, are the mucosa, submucosa, muscularis, and serosa.
- The mucosa is the innermost layer that surrounds the lumen. Its primary functions are secretion and absorption. This layer consists mainly of epithelium, which can secrete digestive enzymes and mucus, and it is responsible for the absorption of nutrients and water.
- The submucosa lies immediately beneath the mucosa and is composed of dense connective tissue containing blood and lymphatic vessels that transport absorbed nutrients. It also contains nerves within the submucosal plexus and can have submucosal glands that release digestive secretions.
- The muscularis, also known as the muscularis externa, includes a double layer of smooth muscle in the small intestine—an inner circular layer and an outer longitudinal layer—contributing to mechanical digestion and the movement of food along the canal through peristalsis. In parts of the alimentary canal, skeletal muscle is present, allowing voluntary control such as in swallowing and defecation.
- The serosa is the outermost protective layer continuous with the mesentery. It provides lubrication to reduce friction from muscle movements and protection against external environments.
Therefore, the correct sequence and functions of the layers from innermost to outermost are: A) Mucosa - absorption and secretion, B) Submucosa - contains blood vessels and nerves, C) Muscularis - responsible for peristalsis, D) Serosa - outermost protective layer.