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The USMLE classically asks question that requires the knowledge of the differences between the upper half (or two thirds) of the anal canal and the lower half (or one third) of the anal canal.
They have different embryonic origins, epithelial lining, nerve supply, venous drainage, arterial supply, and lymphatic drainage.
The line that marks the boundary between the two is called the Pectinate Line.
It's important not to confuse this line with the Hilton's White Line. The Hilton's White Line is an anatomical landmark that marks the change between unkeratinized stratified squamous epithelium (mucosa) above it and the keratinized stratified squamous epithelium (skin) below it. It also marks the border between the internal and external anal sphincters.
Here's a Table that lists the differences;
They have different embryonic origins, epithelial lining, nerve supply, venous drainage, arterial supply, and lymphatic drainage.
The line that marks the boundary between the two is called the Pectinate Line.
It's important not to confuse this line with the Hilton's White Line. The Hilton's White Line is an anatomical landmark that marks the change between unkeratinized stratified squamous epithelium (mucosa) above it and the keratinized stratified squamous epithelium (skin) below it. It also marks the border between the internal and external anal sphincters.
Here's a Table that lists the differences;
