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.

ANATOMY
Anatomic divisions of the large intestine:
1. Colon
2. Rectum
3. Anal canal
Layers of the colon and rectum:
1. Mucosa
2. Submucosa
3. 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.
Thursday, April 7, 2016 4DR. RUBEL, SSMC

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

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 branches
a. 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).

Colorectal and Anorectal Vascular Supply-contd.
3. Internal iliac artery branches
a. 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.

Venous drainage
Except 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.

Colorectal and Anorectal Lymphatic Drainage
The 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

Colorectal and Anorectal Nerve Supply
The 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.

Rectum anatomy

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