give the diagrammatic representation of walls of alimentary canal and explain it
Answers
The GI tract is composed of four layers. Each layer has different tissues and functions. From the inside out they are called: mucosa, submucosa, muscularis, and serosa.
MUCOSA
The mucosa is the innermost layer, and functions in absorption and secretion. It is composed of epithelium cells and a thin connective tissue.
The mucosa contains specialized goblet cells that secrete sticky mucus throughout the GI tract. On the mucosa layer, small finger-like projections called villi and microvilli help to increase surface area for nutrient absorption.
SUBMUCOSA
The submucosa is relatively thick, highly vascular, and serves the mucosa. The absorbed elements that pass through the mucosa are picked up from the blood vessels of the submucosa.
The submucosa also has glands and nerve plexuses. The submucosa lies under the mucosa and consists of fibrous connective tissue, separating the mucosa from the next layer, the muscularis externa.
MUSCULARIS EXTERNA
The muscularis externa is responsible for segmental contractions and peristaltic movement in the GI tract. These muscles cause food to move and churn together with digestive enzymes down the GI tract. The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer. It should not be confused with a thin layer of muscle known as the muscularis mucosa, which lies within the submucosa, a layer of tissue adjacent to the muscularis externa. The muscularis mucosa is made up of smooth muscle, and is most prominent in the stomach.
Within the muscularis externa, the circular muscle layer prevents food from traveling backward, while the longitudinal layer shortens the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.
The coordinated contractions of these layers is called peristalsis.
SEROSA
In anatomy, the serous membrane (or serosa) is a smooth membrane that consists of a thin connective tissue layer and a thin layer of cells that secrete serous fluid. Serous membranes line and enclose several body cavities, known as serous cavities, where they secrete a lubricating fluid to reduce friction from muscle movements.
Serosa is not to be confused with adventitia, a connective tissue layer that binds together structures rather than reduces friction between them.
