USMLE Step 1 Review 04 10 Anatomy Pectinate Line

USMLE Step 1 Review 04 10 Anatomy Pectinate Line


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Let’s continue our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3 04 10 Anatomy Pectinate Below


Begin 04 10 Anatomy Pectinate Transcription

What structure inside the rectum marks the end of the rectum and the beginning of the anatomical anal canal?

  • The pectinate or dentate line.

Because this line marks the junction of the rectum and the anus, it is also called?

  • The anorectal line.

What is the shape of this pectinate or dentate line?

  • It is a circular zigzag going horizontally around the top of the anatomical anal canal. Now the pectinate or dentate line marks the transition zone between two types of tissue lining the rectum or the anus. Now the tissue lining the rectum above is the same kind of mucosal tissue as in the rest of the rectum.

However, the tissue lining the anal canal below the pectinate or dentate line is what kind of epithelium?

  • Non-keratinized, stratified squamous epithelium devoid of hairs. Now the pectinate or dentate line, this zigzag form, is caused by fingerlike, pouched projections of tissue from the anal canal projecting upward into the rectal canal with troughs in between.

Now these fingerlike projections up into the rectal area which is mucosa raised up into longitudinal folds is called?

  • The anal columns.

These anal columns however are not covered with the non-keratinized stratified squamous epithelium of the anal canal. They are more likely to be covered by the mucosa common to the rectum. The dentate or pectinate line actually zigzags along the base of the columns, going up a little bit with the columns and then dropping down a little bit with the base of the troughs between the columns. One way to visualize this area is to think of the troughs like as if you had put fingers pointing down and pressed into the surface of the mucosa rather like pressing fingers into clay. In between these troughs pointing downward like fingerlike impressions then, you have fingerlike extrusions pointing up.



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