Figure 2.

Comparison between oral (both lining and masticatory, respectively a,b) and bowel (both small and large, respectively c,d) mucosae. Above: Original pictures, hematoxylin and eosin stainings; bar: 100 micra. Original magnifications: 100×. Below: drawings summarizing the main characteristics of these tissues. In detail, the epithelium of oral mucosa is a stratified squamous epithelium, non-keratinized in the lining mucosa (a) and keratinized in the masticatory mucosa (b). It is divided into four layers: basal layer, prickle-cell layer, intermediate layer and superficial layer for lining mucosa; and basal layer, prickle-cell layer, granular layer and superficial (keratinizing) layer for masticatory mucosa. In both epithelia, the basal layer consists of cuboidal or columnar keratinocytes that are capable of division so as to maintain a constant epithelial population. Cells arising by division in the basal layers of the epithelium undergo a process of maturation as they are passively displaced toward the surface. In the non-keratinized squamous epithelium, the cytoplasm of intermediate cells does not contain keratin filaments. In keratinizing epithelium, the granulosum stratum is prominent and cells contain intracytoplasmic granules of keratohyaline. The epithelium of small bowel (c) covers the intestinal villi and the crypt compartments; it is columnar and composed of various cell types, such as absorptive cells, goblet cells and endocrine cells, in the villi, and stem cells and Paneth’s cells, in the crypts. The epithelium of large bowel (d) covers glandular crypts; it is composed of a single layer of columnar cells and consist of absorptive cells that are responsible of water and ion transport, and goblet cells.