Title: Digestive system – Histology
Headings: 12
Digestive system

12 Digestive system
Four layers of digestive tract walls
Mucosa
Submucosa
Muscularis externa
Adventitia
Regional histology of the digestive tract
Esophagus
Stomach
Small intestine
Large intestine
Region
Histological characteristics
Esophagus
Stomach
Small Intestine
Large Intestine

Content: The mucosa of the small intestine has some adaptations to the functions it serves. It is heavily creased into the structures that increase the surface area where the nutrients are digested and absorbed. These adaptations include intestinal folds called the plicae circulares, villi, and microvilli. The plicae circulares are folds of mucosa and submucosa that extend into the intestinal lumen. They encircle the entire intestine and are visible without a microscope, so they will not be discussed here. Villi are microscopic fingerlike projections of the mucosa covered in simple columnar epithelium. Microvilli are tiny cytoplasmic extensions on the external surface of epithelial cells. They are barely recognizable under a light microscope as a striated layer on top of the epithelial cells and are called brush (striated) border. Figure 8: Villi in the jejunum
All three segments of the small intestine are covered by simple columnar epithelium.