RECTUM ANATOMY

INTRO

• The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine .

• The human rectum is about 12 centimetres (4.7 in) long,• [2] and begins at the rectosigmoid junction (the end of the sigmoid

colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used.[

• 3] Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla.

• It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used.[

• 3] In humans, the rectum is followed by the anal canal, before the gastrointestinal tract terminates at the anal verge.

ANATOMYAnatomic divisions of the large intestine:

1. Colon2. Rectum3. Anal canal

Layers of the colon and rectum:1. Mucosa2. Submucosa3. Inner circular muscle – Coalesces distally to create the internal anal sphincter.4. Outer longitudinal muscle – Separated into three teniae coli in the colon; teniae converge proximally at the appendix and distally at the rectum.5. Serosa – Covers the intraperitoneal colon and one third of the rectum.

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SUPPORTS

• Supports of the rectum include:[citation needed]

• Pelvic floor formed by levator ani muscles.• Waldeyer's fascia• Lateral ligaments of rectum which are formed by

the condensation of pelvic fascia• Rectovesical fascia of Denonvillers, which extends

from rectum behind to the seminal vesicles and prostate in front.

• Pelvic peritoneum• Perineal body

PERITONEAL COVERING

FASCIA

• 1. DENOVILLIER- ant

• 2.WALDEYER- post

DENOVILLIER FASCIA

• The rectoprostatic fascia is a membranous partition at the lowest part of the rectovesical pouch.

• It separates the prostate andurinary bladder from the rectum.[1]

• It consists of a single fibromuscular structure with several layers that are fused together and covering the seminal vesicles.

• It is also called Denonvilliers' fascia after French anatomist and surgeon Charles-Pierre Denonvilliers.[2]

• The structure corresponds to the rectovaginal fascia in the female.

• The rectoprostatic fascia also inhibits the posterior spread of prostatic adenocarcinoma; therefore invasion of the rectum is less common than is invasion of other contiguous structures.

WALDEYERS FASCIA

• The presacral fascia lines the anterior aspect of the sacrum, enclosing the sacral vessels and nerves.

• It continues anteriorly as the pelvic parietal fascia, covering the entire pelvic cavity.[3]

• It has been erroneously described as the posterior aspect of the mesorectal fascia.[4]

• These two fascias are in fact, separate anatomical entities.• During rectal surgery and mesorectum excision, dissection

along the avascular aveolar plane between these two fascias, facilitates a straightforward dissection and preserves the sacral vessels and hypogastric nerves.

• The presacral fascia is limited postero-inferiorly, as it fuses with the mesorectal fascia, lying above the levator ani muscle, at the level of the anorectal junction.[5

• ] The colloquial term, among colo-rectal surgeons, for this inter-fascial plane, is known as the "holy plane" of dissection first coined by Heald RJ.[6]

• The mesorectal fascia, also known as the fascia propria or the pelvic visceral fascia, has been originally described as the fascia recti in Waldeyer's publication, Das Becken.

• Fascia recti is also a term commonly used among French surgeons to describe the mesorectal fascia.[7] Confusingly, fascia recti is described in some anatomy books, referring to the fascia of the rectus abdominis muscle.

• Identification and preservation of the Waldeyer’s fascia is of fundamental importance in preventing complications and reducing local recurrences of rectal cancer.[8] Hence attention to this anatomy is essential in contemporary rectal surgery.

VALVES OF HOUSTON

• The transverse folds of rectum (or Houston's valves) are semi-lunar transverse folds of the rectal wall that protrude into the rectum, not the anal canal as that lies below the rectum.

• Their use seems to be to support the weight of fecal matter, and prevent its urging toward the anus, which would produce a strong urge to defecate.

• Although the term rectum means straight, these transverse folds overlap each other during the empty state of the intestine to such an extent that, as Houston remarked, they require considerable maneuvering to conduct an instrument along the canal, as often occurs in sigmoidoscopy and colonoscopy.

• These folds are about 12 mm. in width and are composed of the circular muscle coat of the rectum. They are usually three in number; sometimes a fourth is found, and occasionally only two are present.

• One is situated near the commencement of the rectum, on the right side.

• A second extends inward from the left side of the tube, opposite the middle of the sacrum.

• A third, the largest and most constant, projects backward from the forepart of the rectum, opposite the fundus of the urinary bladder.

• When a fourth is present, it is situated nearly 2.5 cm above the anus on the left and posterior wall of the tube.

• Transverse folds were first described by a British anatomist John Houston, a curator of Dublin College of Surgeon's Museum, in 1830. They appear to be peculiar to human physiology: Baur (1863) looked for Houston's valves in a number of mammals, including wolf, bear, rhinoceros, and several Old World primates, but didn't find any. They are formed very early during human development, and may be visible in embryos of as little as 55 mm in length (10 weeks of gestational age.)[

RECTAL AMPULLA

• The rectal ampulla (or ampulla recti) is the dilated section of the rectum where feces are stored until they are eliminated via theanal canal. The caliber of the rectum at its commencement is similar to that of the sigmoid colon, but near its termination it dilates, forming the ampulla. An ampulla is a cavity, or the dilated end of a duct, shaped like a Roman ampulla.

Colorectal and Anorectal Vascular Supply

The arterial supply to the colon is highly variable. In general, the arterial supply to the colon is as follows:1. Superior mesenteric artery branches

a. Ileocolic artery (absent in up to 20 percent of people) supplies blood flow to the terminal ileum and proximal ascending colon.b. Right colic artery supplies the ascending colon.c. Middle colic artery supplies the transverse colon.

2. Inferior mesenteric artery branchesa. Left colic artery supplies the descending colon.b. Sigmoidal branches supply the sigmoid colon.c. Superior rectal artery supplies the proximal rectum.

The terminal branches of each artery form anastomoses with the terminal branches of the adjacent artery and communicate via the marginal artery of Drummond (complete in only 15–20 percent of people).

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Colorectal and Anorectal Vascular Supply-contd.

3. Internal iliac artery branchesa. Middle rectal artery (variable presence and size).b. Internal pudendal artery branch.

i. Inferior rectal artery supplies the lower rectum and anal canal.

A rich network of collaterals connects the terminal arterioles of each of these arteries, thus making the rectum relatively resistant to ischemia.

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Venous drainageExcept for the inferior mesenteric vein, the veins of the colon, rectum, and anus parallel their corresponding arteries and bear the same terminology.

The inferior mesenteric vein ascends in the retroperitoneal plane over the psoas muscle and continues posterior to the pancreas to join the splenic vein. The venous drainage of the rectum parallels the arterial supply.

The superior rectal vein drains into the portal system via the inferior mesenteric vein.

The middle rectal vein drains into the internal iliac vein.

The inferior rectal vein drains into the internal pudendal vein, and subsequently into the internal iliac vein.

A submucosal plexus deep to the columns of Morgagni forms the hemorrhoidal plexus and drains into all three veins.

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Colorectal and Anorectal Lymphatic DrainageThe lymphatic drainage of the colon originates in a network of lymphatics in the muscularis mucosa.Lymphatic vessels and lymph nodes followthe regional arteries.

Lymphatic channels in the upper and middle rectum drain superiorly into the inferior mesenteric lymph nodes.

Lymphatic channels in the lower rectum drain both superiorly into the inferior mesenteric lymph nodes and laterally into the internal iliac lymph nodes.

The anal canal has a more complex pattern of lymphatic drainage. Proximal to the dentate line, lymph drains into both the inferior mesenteric lymph nodes and the internal iliac lymph nodes.

Distal to the dentate line, lymph primarily drains into the inguinal lymph nodes, but also can drain into the inferior mesenteric lymph nodes and internal iliac lymph nodes

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Colorectal and Anorectal Nerve SupplyThe nerves to the colon and rectum parallel the course of the arteries.

1. Sympathetic (inhibitory) arise from T6-T12 and L1-L3.

2. Parasympathetic (stimulatory) innervation to the right and transverse colon is from the vagus nerve; parasympathetic nerves to the left colon arise from sacral nerves S2–S4 to form the nervi erigentes.

The external anal sphincter and puborectalis muscles are innervated by the inferior rectal branch of the internal pudendal nerve. The levator ani receives innervation from both the internal pudendal nerve and direct branches of S3–S5.

Sensory innervation to the anal canal is provided by the inferior rectal branch of the pudendal nerve. Whereas the rectum is relatively insensate, the anal canal below the dentate line is sensate.

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