Final answer:
The walls of the GI tract are composed of four layers of tissue: mucosa, submucosa, muscularis externa, and serosa, each contributing to the process of digestion and absorption.
Step-by-step explanation:
The walls of the organs of the GI tract consist of four distinct layers of tissue. Starting from the lumen and moving outwards, the layers are as follows:
- Mucosa—the innermost layer which contains epithelium capable of secretion and absorption, playing a pivotal role in both digesting and transporting nutrients and water.
- Submucosa—a layer that consists of connective tissues, blood vessels, and nerves, supporting the mucosa.
- Muscularis externa (or muscularis)—a double layer of smooth muscle in the small intestine, including an inner circular layer and an outer longitudinal layer, which are responsible for peristalsis and mechanical digestion.
- Serosa—the outermost layer, a thin sheath of connective tissue that separates the GI organs from surrounding cavities and tissues.
These layers work together to enable digestion, absorption, and transport of food substances throughout the alimentary canal.