Anatomy, Abdomen and Pelvis, Rectum

Article Author:
Yun Hwa Wang

Article Editor:
Jeffrey Wiseman

Editors In Chief:
Sebastiano Cassaro
Joseph Lee
Tanya Egodage

Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Pritesh Sheth
Hassam Zulfiqar
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes
Kavin Sugumar

2/1/2019 6:59:21 PM


The rectum is the most distal portion of the large intestine, bound by the sigmoid colon proximally and converging into the anal canal distally. This segment of intestine derives its name from Latin intestinum rectum meaning “straight intestine,” describing its course compared to the tortuous appearance of the rest of the gastrointestinal (GI) tract. Coursing within the pelvis, the rectum is the most posterior visceral organ in the pelvic cavity with differing anatomical relationship to male and female structures.

Structure and Function

The rectum starts at the level of S3 around the sacral promontory as a continuation of the sigmoid colon. This portion of the GI tract is differentiated from the colon by the coalescence of taenia coli where the muscular bands spread to form the outer longitudinal muscle layer of the rectum.[1]  The rectum measures between 12 to 15 cm in length from the rectosigmoid junction to the dentate line in the anal canal. Its course is marked by two anterior-posterior flexures, with the rectum first following the concavity of the sacrum at the sacral flexure and later coursing with an anterior convexity at the anorectal flexure. There are also three lateral flexures, made by submucosal folds in the lumen called valves of Houston, often two on the left and one on the right.[1]  The final portion of the rectum is the ampulla, which is an expanded segment that rests on the pelvic diaphragm. The rectum transitions to the anal canal at the level of the levator ani muscle.

The peritoneum covers the upper third of the rectum anteriorly and laterally, but the of the middle third is only covered anteriorly. The lower third is not covered by peritoneum but starting at this level, the fascia propria envelops this segment of the rectum. This fascia is more pronounced laterally, forming the lateral rectal stalks. The rectum is attached posteriorly to the presacral fascia at the level of S4 via the Waldeyer fascia.[2]

The peritoneal reflection is variable between individuals but is generally six to eight cm from the anal verge. In men, the reflection of the peritoneum to posterior bladder forms the rectovesical pouch. In women, the reflection is from the rectum to the posterior cervix forming the rectouterine pouch, also known as the pouch of Douglas.

The rectal wall consists of five layers, starting from the lumen: the mucosa, deep mucosa, submucosa, muscularis propria, and serosa where covered by peritoneum. An inner circular, and outer longitudinal muscular layer comprise the muscularis propria. The inner circular layer thickens at the anorectal junction, forming the internal anal sphincter while the outer layer continues as the longitudinal layer of the anal sphincter.[2]

The rectum functions primarily as a temporary reservoir for feces storage. It also plays an integral role in controlling defecation as well as maintaining continence.[2]


The rectum derives from the hindgut, which also gives rise to the segment of the GI tract from transverse colon down to the dentate line.[3]

Blood Supply and Lymphatics

The inferior mesenteric artery (IMA), the most distal branch of abdominal aorta before its bifurcation, ends as the superior rectal (hemorrhoidal) arteries. This artery supplies the rectum and upper third of the anal canal. The rectum receives additional vascular contributions from the middle rectal artery, which is a branch of the internal iliac artery, supplying the distal rectum and proximal anal canal. The inferior rectal artery comes off the internal pudendal artery, which is also a branch of the internal iliac artery. Collaterals between the inferior and superior hemorrhoidal arteries exist at the level of the dentate line, making the incidence of rectal ischemia low.[2]

Venous drainage of the rectum accompanies the arterial supply. Blood drains from the rectum in either the systemic or portal system. The majority of blood from rectum drains into the superior rectal vein that drains into the portal system through the inferior mesenteric vein. The distal portion of the rectum and anal canal has drainage through the middle and inferior rectal veins into the internal iliac veins via the pudendal vein.[1]

The lymphatic drainage of the rectum follows the arterial supply as well. The rectum drains into the superior rectal lymphatics to the retroperitoneal inferior mesenteric lymph nodes. Additionally, the middle and inferior hemorrhoidal vessels have lymphatic drainage into the internal iliac nodes. Below the dentate line in the anal canal, the lymph drains to the inguinal nodes.[1]


The rectum has autonomic innervation from sympathetic and parasympathetic fibers. The sympathetic innervation is from the lumbar splanchnic nerves originating at L1 to L2. Preganglionic sympathetic fibers follow the pathway of the IMA to innervate left colon and rectum. They join to form the preaortic and superior hypogastric plexuses. The nerve fibers from these plexuses enter rectum laterally to provide sympathetic innervation to the lower rectum.[2]

Parasympathetic supply originates from the sacral region and courses anteriorly to join the sympathetic fibers forming the pelvic plexus. Postganglionic parasympathetic and sympathetic fibers then distribute to the rectum through the inferior mesenteric plexus.[2]


The rectum is supported by the pelvic floor muscles, which also aid in the process of defecation and continence. The levator ani muscles comprise much of the pelvic floor; these are the iliococcygeus, pubococcygeus, and puborectalis muscle.[4]

Surgical Considerations

Anatomical location of rectal cancer is critical as it dictates the surgical approach. Rectal tumors located in the upper and middle third are manageable with procedures sparing the anal sphincter, such as low anterior resection surgery.[5] Tumors located in the lower rectum, within 5 cm of the anal verge, however, may require an abdominal perineal resection in which the rectal cancer along with normal rectum and anal sphincter is resected through the perineum, resulting in a permanent colostomy.[5]

During surgical dissection, nerves are at risk of injury leading to sexual dysfunction in men with symptoms of erectile or ejaculatory dysfunction.[5]  There are several potential sites for nerve injury during rectum resection. The first potential site of injury is at the origin of the IMA. The purely sympathetic hypogastric plexus lies in this area; therefore, an injury could occur during ligation of the IMA pedicle causing retrograde ejaculation.

In the dissection of the posterior plane of the rectum, rectal dissection is outside the fascia propria. Nerves sit adjacent to this plane of dissection and are easily injured if the surgeon does not take the correct dissection plane. Injury at this location results in purely sympathetic damage as the parasympathetic fibers have not yet joined.[5]

In the anterior dissection of the rectum, the fascia between the rectum and the prostate alongside the seminal vesicles is divided; this is a very narrow space which is difficult to access, resulting in potential damage to mostly parasympathetic fibers causing impotence as the anterior dissection goes deeper into the pelvis.[5]

Clinical Significance

The anatomical position of the rectum is vital in the digital rectal exam in men. The prostate sits anterior to the wall of the rectum, which allows for manual palpation to assess for nodules, shape, and size of the prostate in carcinoma screening. In women, the cervix, uterus, and vagina sit anteriorly to the rectum, and a digital rectal exam is often in conjunction with the manual pelvic exam. Posterior vaginal wall weakening could result in a rectocele where the rectum herniates into the vagina.  

  • Image 3563 Not availableImage 3563 Not available
    Contributed by Gray's Anatomy Plates
Attributed To: Contributed by Gray's Anatomy Plates

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Anatomy, Abdomen and Pelvis, Rectum - Questions

Take a quiz of the questions on this article.

Take Quiz
An anal fistulotomy is recommended for a 43-year-old male with an anorectal abscess. What artery supplies the anal canal above the dentate line?

Click Your Answer Below

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Sign Up
A 65-year-old male patient recently diagnosed with rectal cancer within 1 cm of the anal canal undergoes CT imaging for the staging. Results of CT reveal a possible extension beyond the rectal wall. If rectal cancer is metastatic, which of the following group of lymph nodes would most likely contain the cancerous cells?

Click Your Answer Below

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Sign Up
A 65-year-old male with rectal carcinoma located 6 cm from anal canal undergoes low anterior resection surgery. The patient recovers well and is subsequently discharged home. During the follow-up visit, he mentions an inability to have an erection. Possible injury to the nerves originating from what of the following region is most likely responsible for the erectile dysfunction?

Click Your Answer Below

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Sign Up

Anatomy, Abdomen and Pelvis, Rectum - References


Barleben A,Mills S, Anorectal anatomy and physiology. The Surgical clinics of North America. 2010 Feb;     [PubMed]
Stoker J, Anorectal and pelvic floor anatomy. Best practice     [PubMed]
Kahai P,Bhimji SS, Anatomy, Abdomen and Pelvis, Large Intestine 2018 Jan;     [PubMed]
Bordoni B,Leslie SW, Anatomy, Abdomen and Pelvis, Pelvic Floor 2018 Jan;     [PubMed]
Lindsey I,Guy RJ,Warren BF,Mortensen NJ, Anatomy of Denonvilliers' fascia and pelvic nerves, impotence, and implications for the colorectal surgeon. The British journal of surgery. 2000 Oct;     [PubMed]


The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Surgery-General. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Surgery-General, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Surgery-General, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Surgery-General. When it is time for the Surgery-General board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Surgery-General.