Anatomy of the gastrointestinal organs of the pelvis and perineum

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Anatomy of the gastrointestinal organs of the pelvis and perineum

USMLE® Step 1 questions

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GI Organs of the Pelvis

Figure 1. A Anterolateral view of the pelvis showing structures that support the rectum. B Lateral diagrammatic view of the pelvis showing the puborectalis muscle.
Figure 2. A Anterior view of the rectum in coronal section with the anterior wall removed. B Midsagittal section of a female pelvis.
Figure 3. A Anterior view of rectum in coronal section and B close-up of the anal canal.
Figure 4. Anterior view of the rectum showing the A arterial supply and B venous drainage.
Figure 5. Midsagittal view of the A male and B female pelvis (with rectum intact).
Unlabelled Figures


USMLE® Step 1 style questions USMLE

of complete

An investigator is studying the embryology of the gastrointestinal tract and discovers an anatomical line called the pectinate line within the anal canal. Which of the following best characterizes the region of the anal canal above the pectinate line?  


When you eat, food travels over 15 feet before leaving your body! But before it leaves, it has two final stops; the rectum and the anal canal. Let’s explore these gastrointestinal organs of the pelvis and discuss the process of defecation and the structures involved.

The rectum is the terminal chamber of the large intestine that temporarily stores feces before defecation. The rectum joins with the sigmoid colon at the level of S3, forming the rectosigmoid junction.

Then, the rectum courses below in the pelvic cavity, reaching a point anterior and inferior to the tip of the coccyx. Here, the rectum pierces the levator ani muscle to join with the anal canal, forming the anorectal junction.

Let’s think of the pelvis like a bowl. The levator ani muscle acts as the bottom of the bowl to support the structures within the pelvis, especially the rectum.

Another structure that supports the rectum is the anococcygeal ligament which forms a fibrous ridge from the anal canal to the coccyx, acting as an anchor.

The relations of the rectum to the surrounding structures differs between biologically male and biologically female individuals.


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  2. "Hollinshead's Textbook of Anatomy" Lippincott Williams & Wilkins (1996)
  3. "Gray's Anatomy" Churchill Livingstone (2007)
  4. "Basic Human Anatomy" W B Saunders Company (1982)
  5. "Applied Radiological Anatomy" Cambridge University Press (2012)
  6. "First Aid for the USMLE Step 1 2014" McGraw-Hill Education (2013)
  7. "Cross-Sectional Imaging of the Anal Sphincter in Fecal Incontinence" American Journal of Roentgenology (2008)

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