The anal canal is an important body part clinically. However, there is no agreement about the epithelium of the anal canal, the anal transitional zone (ATZ) epithelium in particular. The aim of this study is to clarify the structure of the epithelium of the human lower rectum and anal canal. Intact rectum and anus obtained from patients who underwent surgery for rectal carcinoma were examined by light and scanning electron microscopy (LM and SEM). By LM, three types of epithelium were observed in the anal canal: simple columnar epithelium, stratified squamous epithelium, and stratified columnar epithelium. The lower rectum was composed of simple columnar epithelium. SEM findings showed stratified squamous epithelium that consisted of squamous cells with microridges, changing to simple columnar epithelium consisting of columnar cells with short microvilli at the anorectal line. LM and SEM observations in a one-to-one ratio revealed that the area of stratified columnar epithelium based on LM corresponded to the anal crypt and sinus. In conclusion, the epithelium of the human anal canal was fundamentally composed of simple columnar epithelium and stratified squamous epithelium. We found no evidence of the ATZ.

The aim of the present study was to clarify the anatomical structure of the lamina muscularis mucosae (LMM) in the human stomach and to correlate it with the lymphatic spread of gastric cancer cells. Human stomachs taken at operation or autopsy were used. The specimens derived from these stomachs were examined by light microscopy immunohistochemistry and scanning electron microscopy (SEM). In the cardia and pyloric wall, bundles of smooth muscle cells of the LMM were relatively loose and thin and formed a reticular configuration. Small lymphatic capillaries (approximately 10-30 μm in diameter) were present directly above the LMM, and relatively large lymphatics (approximately 80-100 μm in diameter) were observed in the submucosal layer and within the LMM. In contrast, the LMM in the fundus, body, and antral wall was composed of tight, thick bundles of smooth muscle cells that ran straight. Large lymphatics were found directly beneath the LMM, but they were few in the lamina propria mucosae. In addition, lymphatics adjacent to veins were also found in the submucosa of the fundus. Structural differences in the LMM of the stomach wall might depend on physiological function. In this study, the relationship between the cytoarchitecture of the LMM or the distribution of lymphatic vessels and cancer invasion is discussed.

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