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Digestive tract
Abdominal viscera and digestive tract
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Abdominal viscera comprise majority of the alimentary system
o Terminal oesophagus, stomach, pancreas, spleen, liver,
gallbladder, kidneys, suprarenal glands
Liver, stomach and spleen almost fill the domes of the diaphragm, and
receive some protection from the lower thoracic cage
Falciform ligament divides liver into right and left lobes
Greater omentum conceals most of the small intestine
Gallbladder projects inferior of the sharp border of the liver
Food passes from the mouth and pharynx, to the oesophagus and
stomach, where it mixes with gastric secretions
Digestion mostly occurs in the stomach and duodenum
Peristalsis begins in the middle of the stomach and moves toward the
pylorus; mixes masticated food with digestive juices and empties into
duodenum
Absorption occurs in the small intestine, which comprises the
duodenum, jejunum, and ilium
Stomach is continuous with the duodenum, where it receives openings
of ducts from the pancreas and liver
Peristalsis occurs in jejunum and ilium
Large intestine comprises
o Cecum: receives terminal part of ilium
o Appendix
o Colon (ascending, transverse, descending and sigmoid)
o Rectum
o Anal canal
Most reabsorption of water occurs in the ascending colon
Faeces form in the descending and sigmoid colon and accumulate in
the rectum before defecation
GI tract comprises the oesophagus, stomach, small and large intestines
Arterial supply from the abdominal aorta
o Major branches are coeliac trunk and superior and inferior
mesenteric arteries
Superior mesenteric and splenic veins unite to form the hepatic portal
vein (main channel of the portal venous system)
o Drains from abdominal alimentary tract, pancreas, spleen and
most of the gallbladder, and carries to the liver

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Oesophagus
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Muscular tube carrying food from the pharynx to the stomach
Three constrictions where adjacent structures produce impressions
o Cervical (upper oesophageal constriction) at the
pharyngoesophageal junction, due to cricopharyngeous muscle
o Thoracic (broncho-aortic constriction) first crossing of the arch of
aorta, and second crossing by left main bronchus
o Diaphragmatic constriction where it passes through the
oesophageal hiatus
Features of the oesophagus
o Follows curve of the vertebral column as it goes via neck and
mediastinum
o Internal circular and external longitudinal muscle
o External layer of the superior third is voluntary striated muscle;
inferior third is smooth muscle; middle third is both
o Passes through oesophageal hiatus in the muscular right crus of
the diaphragm (left of median plane, T10 level)
o Terminates at entry to the stomach at the cardial orifice of the
stomach (left of midline, 7th costal cartilage, T11)
o Encircled by oesophageal nerve plexus distally
Food passes down via peristalsis, aided by gravity
Oesophagus attached to the oesophageal hiatus by the phrenicooesophageal ligament; allows independent movement of the
oesophagus and diaphragm during respiration and swallowing
Abdominal part of the oesophagus passes from oesophageal hiatus to
the cardial orifice of the stomach, widening as it approaches
o Anterior surface is covered with peritoneum of the greater sac,
continuous with anterior surface of the stomach
o Fits into groove on posterior liver
Posterior part of abdominal oesophagus is covered with peritoneum of
the omental bursa, continuous with posterior surface of the stomach
Right border is continuous with the lesser curvature of the stomach
Left border is separated from the fundus of the stomach by the
cardinal notch
Oesophogastric junction (T11; horizontal with tip of xiphoid process)
o Z-line is where the mucosa changes from oesophageal to gastric
Superior to the z-line, the oesophageal hiatus functions as an inferior
oesophageal sphincter to prevent reflux of gastric contents (contracts)
o When not eating, oesophagus is collapsed, preventing reflux

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Arterial supply of the abdominal part is from the left gastric artery, and
left inferior phrenic artery
Venous drainage from the submucosal veins to the gastric vein, then to
the portal venous system, also to oesophageal veins to azygos vein
then to the systemic venous system
Lymphatic drainage via left gastric lymph nodes, then coeliac nodes
Innervated by oesophageal plexus, formed by vagal trunks, and
thoracic sympathetic trunks via greater splanchnic nerves and
periarterial plexuses

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Stomach
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Expanded part of digestive tract between oesophagus and small
intestine
Accumulates ingested food, and mechanically and chemically digests
it before passage into the duodenum
Gastric juice converts food into semiliquid mix (chime), which passes
into the small intestine

Position, parts and surface anatomy
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In supine position, stomach lies in the right and left upper quadrants; in
the erect position, it move inferiorly
Four parts
o Cardia: part surrounding cardial orifice (T11 level)
o Fundus: dilated superior part, related to left dome of diaphragm;
cardial notch located between oesophagus and fundus
o Body: major part, between fundus and pyloric antrum
o Pyloric part: funnel shaped outflow region; pyloric antrum is the
wider part, leading to the pyloric canal
The pylorus is the sphincter in the distal pyloric part; thickening of
smooth muscle controlling passage of stomach contents through the
pyloric orifice into the duodenum
Intermittent emptying of the stomach occurs when intragastic pressure
overcomes the resistance of the pylorus (normally tonically contracted)
At irregular intervals, gastric peristalsis pushes the chime through the
pyloric canal and orifice into the duodenum
In the supine position, the pyloric part of the stomach lies at the level of
the transpyloric plane (mid between jugular notch and pubic crest)
Two curvatures of the stomach
o Lesser curvature: shorter, concave right border of the stomach;
angular incisure is most inferior part
o Greater curvature: longer convex left border of the stomach

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Interior of the stomach
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Gastric mucosa contains a mucous layer, protecting from acid
contents
When contracted, the mucosa forms gastric folds, most marked in the
pyloric part
During swallowing, a temporary groove called the gastric canal forms,
due to firm attachment of the mucosa to the muscular layer

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Relations of the stomach
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Covered by visceral peritoneum
Two layers of the lesser omentum extend around the stomach and
leave the greater surface as the greater omentum
Anterior relation to the diaphragm, left lobe of liver, anterior abdominal
wall
Posterior relation to the omental bursa and the pancreas
Inferolateral relation to the transverse colon

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Bed of the stomach is formed by structures forming the posterior wall of
the omentum bursa – left dome of diaphragm, spleen, left kidney and
suprarenal gland, splenic artery, pancreas and transverse mesocolon

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Vessels and nerves of the stomach
Arteries
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Arterial supply form the coeliac trunk and its branches
Most blood supply via anastomoses
o Right and left gastric arteries on the lesser curvature
o Right and left gastro-omental (gastro-epiploic) arteries
Fundus and upper body receives blood from short and posterior gastric
arteries

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Veins
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Veins parallel the arteries in position and course
Right and left gastric veins drain into the hepatic portal vein
Short gastric and left gastro-omental veins drain into splenic vein
(which joins superior mesenteric to form the hepatic portal vein)
Right gastro-omental vein drains into the superior mesenteric
Prepyloric vein drains into the right gastric vein

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Lymphatics
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Gastric lymphatic vessels accompany the arteries
Drain from anterior and posterior surfaces to the gastric and gastroomental lymph nodes, which join to the coeliac lymph nodes
Superior 2/3 of stomach drain to the gastric lymph nodes; fundus and
superior body also drain to the pancreaticosplenic nodes
Right inferior third drains to the pyloric nodes
Left inferior third drains to pacreaticoduodenal nodes

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Nerve supply
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Parasympathetic supply from the anterior (left vagus) and posterior
(right vagus) vagal trunks and their branches; enter abdomen via
oesophageal hiatus
Sympathetic nerve supply from T6-9 passes to the coeliac plexus via
greater splanchnic nerve

Small intestine
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Comprises duodenum, jejunum, and ilium
Primary site for nutrient absorption
Extends from pylorus to the ileocecal junction (joins the cecum)

Duodenum
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First, shortest, widest and most fixed part
C-shaped course around the head of the pancreas
Begins at pylorus and ends at the duodenojejunal flexure (L2 level)
o Flexure/junction is an acute angle
Most of the duodenum is fixed by peritoneum to structures on the
posterior abdominal wall; considered partially retroperitoneal
4 parts of the duodenum
o Superior/first part: short, anterolateral to L1 body
o Descending/second part: longer, descends along right sideL1-L3
o Inferior/third part: medium, crosses L3
o Ascending/fourth part: short, begins left of L3 and rises to superior
border of L2
The ampulla is the first 2cm of the superior part of the duodenum; has a
mesentery and is mobile; remainder of duodenum has no mesentery
and is immobile (retroperitoneal)

Superior part
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Ascends from pylorus
Overlapped by liver and gallbladder
Covered by peritoneum on anterior surface and posterior ampulla
Hepatoduodenal ligament attaches superiorly and greater omentum
inferiorly
Relationships
o Level: anterolateral to L1
o Anterior: peritoneum, gallbladder, liver
o Posterior: bile duct, gastroduodenal artery, hepatic portal vein,
IVC

o Superior: gallbladder
o Inferior: pancreas
Descending part
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Runs inferiorly, curves around head of the pancreas
Bile and main pancreatic ducts enter posteromedial wall; ducts unite
to form the hepatopancreatic ampulla which opens on an eminence,
the major duodenal papilla
Entirely retroperitoneal
Relationships
o Level: right of L2/3
o Anterior: transverse colon, transverse mesocolon, small intestine
o Posterior: hilum right kidney, renal vessels, ureter, psoas major
o Superior: superior duodenum
o Inferior: inferior duodenum

Inferior/horizontal part
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Runs transversely from right to left, crossing the IVC, aorta and L3
Crossed by superior mesenteric artery and root of the mesentery of the
jejunum and ileum
Relationships
o Level: anterior to L3
o Anterior: SMA, SMV, small intestine
o Posterior: right psoas major, IVC, aorta and right ureter
o Superior: pancreas, superior mesenteric vessels
o Inferior: small intestine

Ascending part
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Runs superior and along the left border of the aorta to the inferior
border of the body of the pancreas; curves anteriorly to join jejunum
Duodenojejunal flexure supported by the suspensory muscle of the
duodenum (ligament of Trietz); composed of skeletal muscle from the
diaphragm and smooth muscle from the duodenum
Relationships
o Level: L3
o Anterior: beginning of root of mesentery, jejunum
o Posterior: left psoas major, aorta
o Superior: pancreas
o Inferior: jejunum

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Arteries of the duodenum
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Arise from coeliac trunk and superior mesenteric artery
The duodenum up until the entry of the bile duct is supplied by the
superior pancreaticoduodenal artery (branch of gastroduodenal,
arises from coelic trunk)
Duodenum distal to the entry of the bile duct is supplied by the inferior
pancreaticoduodenal artery (branch of superior mesenteric)
Pancreaticoduodenal arteries lie in the curve between the duodenum
and pancreas and supply both structures
Superior and inferior pancreaticoduodenal arteries anastomose
between the entry of the bile duct and the junction of descending and
inferior parts of the duodenum
o Key change in blood supply; proximal area supplied to digestive
tract by coeliac trunk; distal area by the superior mesenteric
o Embryological basis – split of foregut and midgut

Veins of the duodenum
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Follow arteries; drain into hepatic portal vein via superior mesenteric
and splenic veins

Lymphatics of the duodenum
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Follow the arteries
Anterior vessels drain to pancreaticoduodenal and pyloric nodes
Posterior vessels drain to superior mesenteric and coeliac nodes

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Nerves of the duodenum
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Derive from vagus and greater and lesser (abdominopelvic)
splanchnic nerves via coeliac and superior mesenteric plexuses

Jejunum and ileum
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Jejunum begins at duodenojejunal flexure; ileum ends at ileocecal
junction
All intraperitoneal
Most of jejunum in left upper quadrant of infracolic compartment, most
of ileum in the right lower quadrant
No clear demarcation between the two, but distinctive characteristics
that are surgically important
Mesentery is a fan-shaped fold of peritoneum that attaches the
jejunum and ileum to the posterior abdominal wall
Root of the mesentery extends from the duodenojejunal junction on
the left of L2 to the ileocolic junction and right sacroiliac joint
o Crosses ascending and inferior duodenum, aorta, IVC, right
ureter, right psoas major, right testicular/ovarian vessels
o Inbetween the mesentery layers re superior mesenteric vessels,
lymph nodes, autonomic nerves, fat

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Distinguishing features of jejunum and ileum
Characteristic
Colour
Wall
Vascularity
Vasa recta
Arcades
Fat in mesentery
Circular folds
Peyers patches

Jejunum
Deep red
Thick and heavy
Greater
Long
Few large loops
Less
Large, tall, closely
packed
Few

Ileum
Pale pink
Thin and light
Less
Short
Many small loops
More
Low, sparse; absent
distally
Many

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Arterial supply
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Jejunal and ileal arteries, branches of the SMA (arises from aorta at L1)
Arteries unite to form loops/arches called arterial arcades, which give
rise to straight arteries called vasa recta

Venous drainage
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Superior mesenteric vein; unites with splenic vein to form hepatic portal
vein

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Lymphatic drainage
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Lacteals are specialised lymphatic vessels that project into intestinal villi
Drain into lymphatic vessels in the mesentery
o Juxta-intestinal nodes
o Mesenteric nodes (then to superior mesenteric nodes)
o Superior central nodes
Terminal ilium drains to ileocolic nodes

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Nerve supply
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Conducted via periarterial nerve plexus
Sympathetic fibres arise from T8-10, transverse via sympathetic trunks
and thoracic abdominopelvic splanchnic nerves to the superior
mesenteric nerve plexus
o Synapse on coeliac and superior mesenteric ganglia
Parasympathetic fibres arise from posterior vagal trunks, synapsing on
the myenteric and submucosal plexuses in the abdominal wall
SNS stimulation reduces peristalsis and secretory activity, and
vasoconstricts
PNS increases peristalsis and secretory activity, and vasodilates
Insensitive to most pain stimuli apart from distension; perceived as colic
(spasmodic abdominal pain)

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Large intestine
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Water is absorbed from the indigestible residues of chime; converts it to
semi-solid faeces that is temporarily stored
Consists of the following parts
o Omental appendices: small, fatty projections
o Teniae coli: three distinct longitudinal bands
 Mesocolic tenia: transverse + sigmoid mesocolons attach
 Omental tenia: omental appendices attach
 Free tenia: no mesocolons nor omental processes attach
o Haustra: sacculations of colon wall between the tenia
o Large calibre (internal diameter)
Tenia coli begin at the base of the appendix as the thick longitudinal
layer of the appendix splits into three bands
Tenia coli run the length of the large intestine and merge again at the
rectosigmoid junction

Cecum and appendix
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Cecum is first part of large intestine, continuous with ascending colon
Blind pouch in the iliac fossa on right lower quadrant of the abdomen
Close to the inguinal ligament
Enveloped by peritoneum, can be lifted freely, no mesentery
Usually bound to lateral abdominal wall by cecal folds of peritoneum
Ileal orifice enters the cecum through superior and inferior ileocolic
lips/folds, which meet laterally to form ridges (frenula of the ileal orifice)
o Usually closed by tonic contraction, may help prevent reflux
Appendix is a blind intestinal diverticulum containing lymphoid tissue
o Arises posteromedial to the cecum
o Has a short mesentery (meso-appendix), arising from the
posterior side of the mesentery of the terminal ileum

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Arterial supply
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Ileocolic artery, branch of the SMA
Appendicular artery is a branch of the ileocolic

Venous drainage
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Ileocolic vein, a tributary of the SMV

Lymphatic drainage
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Passes to lymph nodes in the meso-appendix and to the ileocolic
lymph nodes , then pass to the superior mesenteric nodes

Nerve supply
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Sympathetic and parasympathetic nerves from the superior mesenteric
plexus
Sympathetic fibres originate at T level, parasympathetic derive from
vagus
Afferents from the appendix accompany the sympathetic nerves to
T10 level

Colon
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Four parts: ascending, transverse, descending and sigmoid
Encircles the small intestine

Ascending colon
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Second part of the large intestine; passes superiorly on the right side
from the cecum to right lobe of the liver, where it turns to left at the
right colic flexure (deep to 9th/10th ribs; overlap by liver)
Secondarily retroperitoneal along right side of posterior abdominal wall
Usually covered by perioneum anteriorly and on sides; short mesentery
in some (25%)
Separated from anterolateral abdominal wall by the great omentum
Right paracolic gutter (groove in peritoneum) lies between the lateral
aspect and the lateral abdominal wall
Arterial supply – ileocolic and right colic arteries (SMA branches)
o Anastomose with each other and other arteries
Venous drainage – ileocolic and right colic veins (SMV tributaries)
Lymphatic drainage – epicolic and paracolic nodes, then ileocolic
and right colic nodes, then superior mesenteric nodes
Nerve supply – superior mesenteric plexus

Transverse colon
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Third, longest and most mobile part
Crosses from right colic flexure to left colic flexure
o Left colic flexure usually more superior; lies anterior to the kidney
and attached to the diaphragm via the phrenicocolic ligament
Transverse colon and the transverse mesocolon loop down, often
inferior to the iliac crests
Mesentery adheres to posterior wall of the omental bursa
Root of the transverse mesocolon lies along the pancreas and
continuous with parietal peritoneum posteriorly
Freely moveable
Arterial supply – middle colic artery (branch of SMA); also from
anastomoses
venous drainage – SMV
Lymphatic drainage – middle colic nodes, then to superior mesenterics
Nerve supply – superior mesenteric nerve plexus; sympathetic,
parasympathetic (vagal) and visceral afferents

Descending colon
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Secondarily retroperitoneal between left colic flexure and left iliac
fossa
Anterior and lateral covering with peritoneum
Short mesentery in some (33%), but not long enough to allow twisting
Paracolic gutter on lateral aspect

Sigmoid colon
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Links descending colon to the rectum (iliac fossa to L3)
Termination of the tenia coli indicates the rectosigmoid junction
Considerable freedom due to long sigmoid mesocolon
Left ureter and division of the common iliac artery are retroperitoneal
Long omental appendices

Arterial supply of descending and sigmoid colon
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Left colic and sigmoid arteries, branches of inferior mesenteric
So at the left colic flexure, there is a second transition in the blood
supply from the SMA (proximal to left flexure) to the IMA (distal to the
left flexure); denotes midgut to hindgut transition

Venous drainage of descending and sigmoid colon
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Inferior mesenteric vein, flowing to splenic and then hepatic portal

Lymphatic drainage of the descending and sigmoid colon
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Epicolic and paracolic nodes, then intermediate colic nodes, then to
inferior mesenterics or superior mesenterics

Nerve supply of the descending and sigmoid colon
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Proximal to left colic flexure, sympathetic and parasympathetic fibres
travel from abdominal aortic plexus
Distal to the left colic flexure, sympathetic and parasympathetic travel
separate
o Sympathetics from lumbar splanchnic nerves, superior
mesenteric plexus and peri-arterial plexuses
o Parasympathetics from pelvic splanchnic nerves via inferior
hypogastrics
Proximal to the middle of the sigmoid colon, visceral pain afferents pass
with thee sympathetic nerves to thoracolumbar ganglia

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Distal to the middle of the sigmoid colon, pain afferents pass with
parasympathetic fibres t vagal sensory ganglia

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Rectum and anal canal
Rectum
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Rectum is the pelvic part of the digestive tract, continuous proximally
with the sigmoid colon and distally with the anal canal
Rectosigmoid junction is at L3 level
Tenai coli spread to form continuous longitudinal layer of smooth
muscle, and omental appendices are discontinued
Follows the curve of the sacrum and coccyx, forming the sacral flexure
Ends anteroinferior to the tip of the coccyx, prior to the anorectal
flexure of the anal canal (occurs as gut perforates pelvic diaphragm)
80o anorectal flexure is important for continence; maintained during
resting state by tone of the puborectalis muscle
Three sharp lateral flexures – superior, inferior and intermediate, formed
in relation to three internal infoldings (transverse rectal folds), which
overlie thickened muscle of the rectal wall
Ampulla of the rectum is the dilated terminal part; supported by levator
ani and the anococcygeal ligament
o Holds accumulating faecal mass until defaecation; relaxes to
accommodate increasing amounts
Peritoneum coverage
o Superior 1/3: anterior and lateral covered
o Middle 1/3: anterior only
o Inferior 1/3: no coverage (subperitoneal)
In both sexes, lateral reflection of peritoneum from the superior 1/3 of
the rectum form pararectal fossae, allowing distension as it fills
Also recto-uterine pouch in females and recto-vesical pouch in males

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Rectum lies posterior to the inferior three sacral vertebrae and coccyx,
anococcygeal ligament, median sacral vessels and inferior
sympathetic trunks and sacral plexuses
In males, rectum related anteriorly to the fundus of the bladder,
terminal ureters, ductus deferentes, seminal glands, and prostate
o Rectovesical septum between fundus of bladder and rectal
ampulla
In females, related anteriorly to the vagina
o Weak rectovaginal septum (inferior to the recto-uterine pouch )
separates the vagina from the rectum

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Arterial supply
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Proximal part via superior rectal artery (continuation of inferior
mesenteric)
Middle and inferior parts via middle rectal arteries (arise from internal
iliac)
Anorectal junction and anal canal via inferior rectal arteries (arise from
internal pudendal)
Anastomoses may provide collateral circulation

Venous drainage
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Superior, middle and inferior rectal veins; superior drain to the portal
venous system and middle and inferior to systemic
Anastomoses between portal and systemic veins in wall of anal canal

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Submucosal rectal venous plexus surrounds the rectum,
communicating with the vesical venous plexus (male) or uterovaginal
venous plexus (female)
Rectal venous plexus has two parts (named rectal, but mostly anal in
location, function, clinical significance)
o Internal: deep to mucosa of anorectal junction
o External: external to muscular wall of the rectum

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Innervation
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Sympathetic supply from lumbar splanchnic nerves and
hypogastric/pelvic plexuses
Parasympathetic supply from S2-4 level via pelvic splanchnic nerves
and inferior hypogastric plexuses
Rectum is inferior to the pelvic pain line, so visceral afferents follow the
parasympathetic fibres retrograde to S2-S4

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Anal canal
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Terminal part of the large intestine and of the entire digestive tract
Extends from superior aspect of pelvic diaphragm to the anus
Begins where the rectal ampulla narrows at the level where the
puborectalis muscle forms a u-shaped sling
Ends at the anus, the external outlet
The anal canal is surrounded by internal and external sphincters, and
descends posteroinferiorly between the perineal body and the
anococcygeal ligament
Collapsed except during passage of faeces; both sphincters must relax
for passage

Internal anal sphincter
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Internal anal sphincter is involuntary, surrounds superior 1/3; is a
thickening of the circular muscle layer
Tonic contraction via sympathetic fibres of the superior rectal and
hypogastric plexuses
Tonic contraction inhibited by parasympathetic stimulation (intrinsically
via peristalsis and extrinsically via pelvic splanchnic innervation)
Relaxes in response to distension of rectal ampulla by faeces or gas,
requiring voluntary contraction of puborectalis and external anal
sphincter if not to occur

External anal sphincter





Large, voluntary muscle forming a broad band on each side of the
inferior 2/3 of the anal canal
Attached anteriorly to the perineal body and posteriorly to the coccyx
via the anococcygeal ligament
Blends superiorly with puborectalis
Subcutaneous, superficial and deep parts

Features





Internally the superior half of the mucosa has longitudinal ridges known
as anal columns, containing terminal branches of the rectal vessels
Anorectal junction is where the rectum joins the anal canal; superior
ends of the anal columns
Inferior ends of anal columns join by anal valves, superior to which are
recesses called anal sinuses
When compressed with faeces, the sinuses secrete mucous to aid
evacuation of faeces from the anal canal



Inferior limit of the anal valves forms the pectinate line, indicating the
junction of superior part of anal canal and inferior part
o Different embryonic origins (hindgut and proctodaeum, thus
different arterial supply, venous drainage, lymph drainage and
innervation

Arterial supply




Superior to the pectinate line via superior rectal artery
Inferior to the pectinate line via the inferior rectal arteries
Middle rectal arteries anastomose with the above

Venous drainage






Internal rectus venous plexus drains in both directions from the
pectinate line
Superior to pectinate line, drains to superior rectal vein (tributary to the
inferior mesenteric)
Inferior to pectinate line, drains to inferior renal veins (tributaries to the
caval venous system)
Muscularis externa of the ampulla drained by middle rectal veins
(tributaries of internal iliacs); also form anastomoses with the above
Normal submucosa of the anorectal junction is thickened due to
sacculated veins of the internal rectal venous plexus
o Forms anal cushions/pads at point of closure
o Pliable and turgid, forming valve to aid closure

Lymphatic drainage



Superior to the pectinate line, drains to internal iliac then to common
iliac and lumbar nodes
Inferior to the pectinate line, drains to superficial inguinal nodes

Innervation




Superior to the pectinate line, sympathetic, parasympathetic and
visceral afferents from the inferior hypogastric plexus
o SNS maintain tone of internal anal sphincter
o PNS inhibit tonus of internal anal sphincter, stimulate peristalsis
o Inferior to the pelvic pain line, so visceral afferents travel with PNS
fibres to S2-4
o Canal sensitive only to stretch – conscious and unconscious
Inferior to pectinate line, somatic innervation from inferior anal (rectal)
nerves (branches of pudendal) – sensitive to pain, touch, temperature

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Reference
1
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Clinically Oriented Anatomy
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