Pectinate Line
The pectinate line, also known as the dentate line, anorectal line, or anocutaneous line, is a serrated line that separates the upper two-thirds (or one half) of the anal canal from the lower one-third (or one-half).
In other words, it is the line between the columnar epithelium of the rectum and the stratified squamous epithelium of the anal canal.
The epithelium of the distal anal canal can also be divided into two parts. The area above the anocutaneous line is lined with non-keratinized stratified squamous epithelium, while the area below is lined with keratinized stratified squamous epithelium.
The pectinate line also forms the base of the anal columns, which are also referred to as anal valves.
The pectinate line is also the embryological junction between the hindgut and proctodeum.
The dentate line is an important anatomical boundary, and there are many differences above and below the line.
| Distinction | Above the Pectinate Line | Below the Pectinate Line |
|---|---|---|
| Lymphatic drainage | Internal iliac lymph nodes | Superficial inguinal lymph nodes |
| Epithelium | Columnar epithelium | Stratified squamous epithelium |
| Embryological origin | Endoderm | Ectoderm |
| Artery | Superior rectal artery < inferior mesenteric artery | Middle and inferior rectal (hemorrhoidal) arteries < internal iliac artery |
| Vein | Superior rectal vein > inferior mesenteric vein > portal system | Middle and inferior rectal veins > internal iliac vein > systemic circulation |
| Hemorrhoids | Internal hemorrhoids (painless) | External hemorrhoids (painful) |
| Nerves | Inferior hypogastric (pelvic) plexus | Inferior rectal nerves |