Upper and Lower Divisions
The anal canal is divided into two unequal sections, upper and lower.
- The upper 2/3 has longitudinal folds or elevations of tunica mucosa. Its mucosa is lined by simple columnar epithelium. Its lower ends are joined together by folds of mucus membrane called anal valves. The upper 2/3 of the anal canal is supplied by the superior rectal artery which is a branch of the inferior mesenteric artery.
- The lower 1/3 of the anal canal is lined by stratified squamous epithelium that blends with the skin. The lower third of the anal canal is supplied by the inferior rectal artery which is a branch of the internal pudendal artery.
A whitish line called Hilton's white line or pecten of Jon Stroud indicates the junction between keratinized stratified squamous epithelium and unkeratinized stratified squamous epithelium.
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