Download Anatomy Exam 1 Lecture 2-Foregut 3 pairs of salivary glands in the

Anatomy Exam 1
Lecture 2-Foregut
 3 pairs of salivary glands in the oral cavity: parotid glands, sublingual glands, and
submandibular glands.
 Thoracic duct, azygous veins, and sympathetic chain ganglia are posterior the
esophagus.
o Anterior is the arch of the aorta, and the heart.
 Dividing line is when the esophagus passes through the diaphragm. Above the
diaphragm the esophagus gets blood supply from thoracic aorta and innervated by
CN IX and X. After it passes into the diaphragm there is no true sphincter where the
esophagus enters into the stomach.
o Innervation does not change after the diaphragm.
o Portal veins drain esophagus (vena cava superior to diaphragm).
o Passes through diaphragm at the level of T10.
 GI tube is divided into three sections based upon primary arterial supply.
 All venous drainage is normally through the portal vein into the liver to filter blood
from all things absorbed in the GI tract, it helps complete digestion and detoxifies
blood.
 Parts of GI Tract
o First part (foregut) includes the distal esophagus, stomach, 1st half of
duodenum, liver, gallbladder, spleen and pancreas.
 Arterial supply from the celiac trunk!
o Second part (midgut) includes the distal duodenum, jejunum, ileum, cecum,
appendix, 2/3 of transverse colon and ascending colon.
 Arterial supply from superior mesenteric artery.
o Third part (hindgut) includes the distal transverse colon, descending colon,
sigmoid colon, and proximal rectum.
 Arterial supply from inferior mesenteric artery
 When the abd cavity is first opened, all that is visible is the greater omentum, a
fused double fold of the dorsal mesentery. Infections in this area are very
dangerous because there is no blood supply here and does not protect against
infections.
o Falciform ligament attaches liver to anterior body wall and is a remnant of
the ventral mesentery.
 Greater Omentum
o Several named parts:
o Gastrophrenic ligament-attaches stomach to the diaphragm
o Gastrosplenic ligament-attaches stomach to the spleen
o Gastrocolic ligament-suspends the transvers colon from the stomach. Major
blood vessels that feed the stomach travel through this ligament.
 Lesser Omentum
o Remnant of the ventral mesentery and has several named parts.
o Gastrohepatic ligament-connects the stomach to the liver
o Hepatoduodenal ligament
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o Lesser Sac of abdomen
 Foramen of Windslow
 Pancreas, spleen, stomach, transverse colon, left kidney are the organs
contained in the lesser sac.
 Posterior surface of stomach is more prone to ulceration which is
dangerous.
Omentum and compartments of the GI cavity
o Supracolic compartment-stomach, distal esophagus
o Infracolic compartment-most of GI tube is here, most of the accessory organs
are supracolic.
Stomach
o Distal esophagus connects to stomach with no true sphincter between them.
Stomach is just an expanded part of the tube.
o Named regions of the stomach:
 Fundus-at the top
 Greater curvature
 Angular notch
 Pyloric antrum
 Pyloric canal
 Cardiac
 Body
o Multiple muscle layers, makes peristalsis a three dimensional action, looks
like wringing out a washcloth. Produces chyme.
o Internal surface has numerous folds called rugae. These secrete acid to
dissolve food and mucus to protect itself. True sphincter separates the
stomach from the small bowel, called the pyloric sphincter.
o Relationships-posterior is the spleen, pancreas, left kidney, abdominal aorta,
inferior vena cava.
Duodenum
o First part of the small bowel, connected to the liver/gallbladder and
pancreas.
o Described in 4 parts
 Antrum-horizontal part, becomes retroperitoneal. At L1 level
 Descending (L1-L3)-retroperitoneal where accessory organs join.
 Transverse (L3)-retroperitoneal, crosses IVC and aorta
 Ascending (L3-L2)-leads into jejunum, becomes intraperitoneal
nd
o 2 and 3rd parts are retroperitoneal and make direct contact with posterior
muscular wall.
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Foregut Vasculature
o Arterial
 Vast majority comes from the celiac trunk and its branches.
 Distal esophagus has anastomotic overlap with esophageal branches
of thoracic aorta.
 Mid-duodenum has anastomotic overlap with branches of superior
mesenteric artery
 Anastomoses are important for alternate route of arterial supply
 Celiac trunk branches into splenic artery, left gastric artery and
common artery.
 Splenic arteryposterior gastric artery and gastro-omental
arteries (supplies greater curvature of the stomach, found in
gastro-colic ligament).
 Left gastric arteryesophageal branch
 Common hepatic arterygastroduodenal artery, proper
hepatic artery and gastro-omental artery.
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o Venous
 All blood flowing to GI tract is supposed to flow back through the liver
via the portal vein.
 Venae comitantes exist but do not enter IVC instead all dump into
portal system for processing in liver.
 Porta-caval anastomoses
 Places where venous blood intended to flow to the liver can be
shunted to the vena cavae, bypassing the liver.
 Important in cases of liver failure, to prevent the liver from
imploding.
 These can develop in: esophagus, rectum, secondarily
retroperitoneal organs, ligamentum teres hepatis (formerly
umbilical vein, can be reopened).
 Shunt venous blood from the GI tract around the liver to the
IVC and SVC; 4 principal sites
 Splenic vein and superior mesenteric vein join to form portal veins.
 Inferior mesenteric vein drains into splenic vein.
 All blood from GI is supposed to pass through portal system.
o Anastomoses
 Left gastric-right gastric, lesser curvature of stomach
 Left gastro-omental-right gastro-omental; greater curvature of
stomach
 Gastrics-gastro-omentals; across body and fundus of stomach
 Short gastrics-posterior gastric-esophageal branch; across posterior
stomach and cardiac region.
 There are other important anastomoses besides the ones with other
celiac branches and allow for collateral arterial flow to GI tract.
 Anastomoses with esophageal branch rom left gastric-esophageal
branches from abdominal aorta.
Foregut Innervation
o Sympathetic
 Greater, lesser, least splanchnic nerves. Pass through the diaphragm
and find ganglia around the celiac trunk called pre- and paraganglions.
 The post-synaptic fibers travel with the arterial branches to the
intestine.
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o Parasympathetic
 Left and right vagus nerves form the vagal trunks, part of the
esophageal plexus.
 Vagus supplies all parasympathetic innervation to the GI tract down
to the distal transverse colon.
 Branches from vagal trunks, then join the celiac and superior
mesenteric artery plexuses to travel with the arterial supply to the
intestine.
Lymphatics
o Lymphatic drainage of the foregut parallels the arteries.
o Drainage is primarily to celiac nodes, which then drain to the lumbar
lymphatic trunks.
o Then drain into the cisterna chylii, then to the thoracic duct.
Lecture 3-Foregut II
 Liver
o Extension of the GI tube, embryologically. Almost all intraperitoneal, except
for a portion on the superior surface next to the diaphragm, here the
peritoneum reflects off the liver to the diaphragm to form the ‘bare area
(secondarily retroperitoneal area).’
o Right lobe is typically larger than the left lobe.
o Falciform ligament divides the two lobes and is a remnant of the mesentery.
Contains the ligamentum teres which is remnant of the umbilical vein.
 In cases of portal hypertension, the umbilical vein can recanalize and
blood can flow into it.
o Posteriorly the caudate and quadrate lobes are present.
o Functions
 Produces bile to help digest fats
 Produces cholesterol
 Helps finish breakdown of materials absorbed from the GI tract
 Detoxifies ingested materials.
o Vasculature of the Liver
 Arterial supply is from the left and right hepatic arteries, which
originate in the celiac trunk.
 Arterial supply does not anastomose between lobes of the liver.
 Arterial branches supply specific segments of the liver (don’t need to
know branches).
 Venous blood from GI tract enters via portal vein, the most blood
entering liver not from arterial supply.
o Innervation
 Mostly autonomic, thoracic splanchnics and vagus.
o Lymphatics
 Liver produces a lot of lymph.
 25-50% of lymph in the thoracic duct.
 Superficial and deep channels
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o Portal triad-bile duct, portal venule and a hepatic arteriole. Always found
grouped together within the liver.
 Begins in the hepatoduodenal ligament.
o Histology
 Liver is made up of a series of overlapping hexagons. The center of
each hexagon is a central vein, which gathers blood that has passed
through the liver from both the hepatic arteris and portal vein.
 These central veins then form the two hepatic veins (one from left,
one from right), which empty into the IVC.
o Biliary System
 Hepatocytes form bile, which are excreted from cells into bile
canaliculi. Canaliculi form interlobular ducts, which join to form
collecting ducts. Collecting ducts merge to form right and left hepatic
ducts.
 Right and left hepatic ducts form the common bile duct, which enters
the second part of the duodenum through the cholecodochal
sphincter. If not open the bile backs up into the cystic duct.
 Bile is stored in gallbladder until pyloric sphincter opens.
 Gallbladder concentrates bile salts and cholesterol by removing water,
if it stays long enough can become crystalized forming gallstones.
o Sphincters
 Sphincter of bile duct
 Sphincter of pancreatic duct
 Sphincter of hepatopancreatic ampulla (sphincter of Oddi)
 These sphincters only relax when chyle is dumbed from the stomach
into duodenum.
Gallbladder
o Innervation
 Mostly autonomic, thoracic splanchnics and vagus.
Pancreas
o Major accessory digestive organ, secretes enzymes into duodenum to aid in
digestion of proteins. Secretes enzymes into vasculature to regulate sugar
metabolism.
o Secondarily retroperitoneal.
o IVC sits posterior to pancreas, don’t want to be eroded! Spleen, diaphragm,
left kidney and liver are all closely related. Alcoholic with pancreatitis should
be concerned with splenic, kidney, duodenal, liver function, etc.
o Anatomy
 3 parts: head, neck, body and tail.
 1 or 2 ducts attaching to the duodenum.
o Vasculature
 Branches of celiac and superior mesenteric artery form an
anastomosis around the pancreas. Effective at supplying blood if
something slowly closes off, however an infarct will result in not
enough blood flow.
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 Venous drainage to splenic or portal vein.
o Innervation
 Purely autonomic, thoracic splanchnics and vagus nerve.
o Lymphatics
 Drain into pacreaticosplenic and celiac nodes.
Spleen
o Lymphoid organ, not digestive. Embryologically forms blood cells.
o Mature spleen is a big player in humoral immunity.
o Scavenges damaged RBCs and recovers iron and heme complexes.
o Very fragile organs and easily damaged in contact sports. Typically removed
when ruptured.
o Vasculature
 Branches of celiac and SMA, these are end arteries and do not
anastomose. If damaged it must be removed, because can’t determine
what has blood flow and what does not.
 Venous drainage to splenic or portal vein.
o Innervation
 Purely autonomic, vagus and thoracic splanchnics.
o Lymphatics is the same as pancreatic.
Clinical Concerns
o Lots of organs that are continually undergoing cell death and division.
o Organs critical for proper digestion.
o Digestive system is primary means for toxins to enter system.
Porta-caval Anastomoses
o All blood flowing to GI tract is supposed to enter portal system and pass
through liver for final processing.
o If the liver is incapable of processing this blood, then the portal system will
increase in pressure. As they swell they will come in contact with caval veins,
which will cause esophageal veins to begin carrying more blood than they
are used too….results in esophageal varices.
o Upper rectal veins drain to portal system, causes build up if unable to drain
will cause internal hemorrhoids.
o Umbilical vein can be recanalized if portal pressure is high enough. Causes
the belly button to swell, results in veins along abdominal wall to swell.
Results in a condition called caput medusa.
o Secondarily retroperitoneal organs (ascending and descending colon,
pancreas and duodenum). Their surface veins are in contact with posterior
abd wall, and when the swell with portal HTN will fuse with posterior abd
wall and cause them to swell. Cannot see this occur.
Fatty liver disease occurs from excessive drinking. Alcohol is stored as fat in the
liver, replacing hepatocytes with fatty cells. Eventually leads to cirrhosis.
Lecture 4-Midgut
 Longest part of the GI tract, ~18-25 feet long. Very mobile.
 Supported only by the mesentery to the posterior abdominal wall.
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Peristaltic action from esophagus down to rectum moves boli along at steady pace.
Mesentery
o Dorsal bilayered fold of peritoneum that attaches the GI tract to the posterior
body wall.
o Forms infracolic gutters which are parallel to mesentery and allows flow of
materials from top to bottom of peritoneum.
o Because this is the only attachment, the vasculature and innervation travel
along the mesentery.
Vasculature
o Originates from the superior mesenteric artery. Contains many, many
branches!
 Superior mesenteric arterymiddle colic, right colic and ileocolic
artery.
o Venae comitantes to portal system.
o Anastomoses between the superior mesenteric artery and the celiac trunk
occurs at the head of the pancreas.
o Ileocolic, right and middle colic arteries all contribute to the arterial arcade
that runs the length of the large bowel, called the marginal artery of
Drummond.
Duodenum
o First and last parts are intraperitoneal, middle is secondarily retroperitoneal.
Transitions from foregut to midgut.
o As the duodenum re-enters the peritoneal space, the bend of the GI tube is
supported by the ligament of Trietz.
o Small bowel has multiple layers in it. From internal to external: circular
foldslamina propriaMuscularis mucosae (circular layerlongitudinal
layersubmucosa)  Muscularis externa (circular layerlongitudinal
layer)  subserosa  visceral peritoneum
Jejunum
o Inner surface of the jejunum is densely lined with folds of mucosa called the
plicae circulares. These are where the absorptive villi are found.
o Arterial supply of jejunum is from the SMA (many small jejunal branches).
 These branches interconnect to form relatively simple arcades that
give rise to the vasa recta or straight vessels (long in jejunum).
Ileum
o As the small bowel continues there are fewer and fewer plicae circulares,
until at the terminal ileum they are non-existent.
o There is also an increase in lymphoid nodules (Peyer’s patches) as the ileum
continues.
o Arterial arcade in the ileal mesentery differs from the jejunal cascade.
o SMA branches join to form a complex arcade, with relatively short vasa recta.
Each vasa recta supplies a very specific region of bowel, with very little
lateral anastomoses. If one of these vessels has an infarct then part of the
bowel will die.
Differences between jejunum and ileum:
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Cecum, Appendix and Ascending Colon
o The ileocecal junction marks the end of the small bowel. The first part of the
large bowel is the terminal part of the midgut.
o Around the 2nd half to last 1/3 of transverse colon the vagus nerve stops
innervating.
o Features of the large bowel include
 Longitudinal muscles called the tenia coli
 External bulges called haustra
 Fatty globs known as appendices epiploicae
 Internally, ridges known as plicae semilunares.
o At the ileocecal junction, the ileum slightly protrudes into the cecum. The
cecum is a large sack.
 The appendix projects off of the end of the cecum and is a blind tube.
 Small lymphatic function
 Host colonies of enteric bacteria reside in the appendix
 Vasculature from the ileocolic artery, has a small branch called the
appendicular artery.
o Innervation
 Autonomic, thoracic splanchnics and vagus.
o Lymphatics
 Found in the mesentery paralleling the arterial supply.
GI tract likes to form adhesions to abdominal wall, especially after surgery.
Peristalsis is always taking place and can result in getting twisted around adhesion
point, called a ‘volvulus.’ A volvulus can result in food being unable to pass, and
blood supply can also be cut off.
Lecture 5-GI Embryology
 Stomach Development
o Foregut starts with an expansion near the celiac trunk. Initially the tube is
the same size, but the enlargement becomes the stomach.
o As it expands it rotates 90 degrees in a clockwise direction around its
longitudinal axis. As a result the ventral border (lesser curvature) moves to
the right and the dorsal border (greater curvature) moves to the left.
o The stomach is suspended dorsally by a dorsal mesentery. As the stomach
rotates the mesentery is carried to the left and forms the omental bursa, or
lesser sac.
Clockwise Rot
Omental Bursa
o The only opening into the omental bursa is through the omental foramen.
o The ventral mesentery begins to break down, removing any attachment to
the anterior abdominal wall. The remnant of the ventral mesentery becomes
the hepatoduodenal ligament, which contains the portal triad.
o The greater omentum is formed by the elongated dorsal mesentery, as the
stomach grows the omental bursa expands and acquires an inferior recess of
the omental bursa between the layers of the greater omentum. This recess
creates four layers of the greater omentum, but later disappears as the layers
fuse together.
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o The pancreas, liver, spleen, and left kidney all form behind the omental
bursa.
Liver Development
o Liver, gallbladder and biliary duct system arise as a ventral outgrowth called
the hepatic diverticulum. The diverticulum extends into the septum
transversum, a mass of splanchnic mesoderm between the developing heart
and midgut. The septum transversum forms the ventral mesentery in this
region.
o The hepatic diverticulum enlarges rapidly and divides into two parts as it
grows between the layers of the ventral mesentery. Ends up becoming a very
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solid organ through a process called branching morphogenesis. This occurs
as the proliferating endodermal cells give rise to interlacing cords of
hepatocytes and to the epithelial lining of the intrahepatic part of the biliary
apparatus. The hepatic cords rapidly expand into blind pouches and
eventually transform into hepatocytes.
o The small caudal part of the hepatic diverticulum becomes the gallbladder,
and the stalk of the diverticulum forms the cystic duct. The stalk connecting
the hepatic and cystic duct to the duodenum becomes the bile duct.
o Hepatic cords, primordial of hepatocytes, grow into the parenchyma of the
septum transversum-ventral mesentery. Hepatic sinusoids, primordial of
vessels, will form veins. At the same time the peritoneal cavity expands,
hollowing out the septum transversum.
o The septum transversum is converted into the ventral mesentery and
remains as the falciform ligament and lesser omentum, passing from the liver
to the lesser curvature of the stomach (hepatogastric ligament) and from the
liver to the duodenum (hepatoduodenal ligament). The umbilical vein passes
in the free border of the falciform ligament.
Gallbladder
o Forms as a diverticulum off the bile duct, diverticulum elongates-forms cystic
duct proximally and gallbladder distally.
Pancreas Development
o The pancreas develops from dorsal and ventral pancreatic buds of
endodermal cells, which arise form the caudal or dorsal part of the foregut.
o Most of the pancreas is derived from the dorsal pancreatic bud, which grows
rapidly between the layers of the dorsal mesentery. The ventral pancreatic
bud develops near the entry of the bile duct into the duodenum and grows
between the layers of the ventral mesentery.
o As the duodenum (distal stomach) rotates to the right and becomes C shaped,
the ventral pancreatic bud is carried dorsally with the bile duct. It soon lies
posterior to the dorsal pancreatic bud and later fuses with it becoming the
uncinate process and part of the head of the pancreas. The pancreatic duct
forms from the duct of the ventral bud and distal part of the duct of the
dorsal bud.
o Sometimes this rotation causes problems. The ventral pancreatic bud can
split creating a bifid pancreatic bud. When the duodenum rotates one half of
the bifid ventral bud will rotate while the other one remains, the two meet
now encircling the duodenum and fuse with each other and the dorsal bud.
Results in stenosis of the duodenum, treated with surgical removal.
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Spleen
o Not part of the GI tube, it is derived from a mass of mesenchymal cells
located between the layers of the dorsal mesentery.
o Mesenchymal cells in the mesogastrium differentiate into the capsule,
connective tissue and splenic cells.
o Ends up suspended from the dorsal mesentery, blood supply comes form the
celiac trunk and venous drainage for portal system.
Midgut Formation
o In the 4th week the duodenum begins to develop from the distal part of the
foregut. The developing duodenum grows rapidly, forming a C-shaped loop
that projects ventrally. As the stomach rotates the duodenal loop rotates to
the right and comes to lie retroperitoneally.
o Beginning in the 5th week, the epithelial cells lining the gut tube proliferate
and fill the lumen of the GI tract completely.
o Vacuoles form in the epithelial cells in the 8th-9th week, recanalization is
usually complete by the end of the 9th week.
 Errors in recanalization can lead to various problems. Most common
is stenosis (narrowing of the lumen) or atresia-complete failure of
recanalization, no lumen present.
 Sometimes during recanalization the lumen can be duplicated, two
separate tubes in one. Can result in cysts forming in one of the tubes,
may grow and cause other obstructions.
 A blind-ended pouch can also be formed, which can result in
infection and abscess
o As the midgut elongates, it forms a ventral, U-shaped loop of the gut that
projects into the umbilicus, creating a ‘physiologic umbilical herniation.’ This
allows room for the small intestine to grow.
o While in the umbilical cord, the midgut loop rotates 90-degrees around the
axis of the superior mesenteric artery. This brings the small intestine of the
midgut loop to the right and the large intestine to the left. During this
rotation the small intestine elongates and forms intestinal loops.
o During the 10th week the intestines return to the abdomen. It is unknown
what causes the intestines to return. Undergoes 2nd 90 degree rotation,
which causes large bowel to be on top and small bowel is curled on bottom.
o During 11th week the GI tract is fully returned to the abd cavity and
undergoes final 90 degree rotation. Duodenum, pancreas, ascending and
descending colon become fixed to the posterior body wall (pushed laterally
and posteriorly by small intestine). Consequently the duodenum has no
mesentery and lies retroperitoneally along with the head of the pancreas.
o This final rotation also ends up with ‘picture-frame’ orientation of the large
intestine. Small intestine continues to elongate and coil.
o Distal part of small intestine is the part that gets flipped around the most.
Appendix also develops during this process. After birth, the wall of the
cecum grows unequally, with the result that the appendix comes to enter its
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medial side but is subject to variation in position. Omphaloenteric duct
attaches the colon to the yolk stalk.
o Errors in Midgut formation
 Omphalocele-persistent herniation of the midgut into the umbilicus.
GI tract is covered with peritoneum and amnion. Requires surgical
correction by returning the intestines back into the abd cavity.
 Gastroschisis-failure of abdominal wall to fuse, usually on the right
side of umbilicus (not in the midline). GI tract is exposed, no
peritoneum covering. Results in the stomach, liver, and GI tract
forming outside of the body. No diaphragm may be formed, and the
thoracic organs are underdeveloped. Has poor survival odds. These
organs must remain external until infant grows large enough for
surgical correction.
 Omphaloenteric fistula is supposed to disappear during development.
 Can result in a blind tube.
 A diverticulum that remains connected to the umbilicus by a
fibrous cord.
 Could remain connected in an open fistula to external
environment.
 Cyst could remain.
 Volvulus of diverticulum can occur.
 Artery attachment to the umbilicus in fibrous cord.
 Malrotation
 Improper malrotation can result in free-floating bowel.
 Volvulus-twisting of intestine
 Superior mesenteric artery compressing transverse colon
resulting in stenosis.
 Cecum may become fixed to the liver.
 Internal herniation, entire small bowel can herniate into the
omental bursa.
 Large intestine is freely mobile and can wrap around small
intestine.
Hindgut Development
o Derivatives of the hindgut are the left 1/3 to ½ of transverse colon, the
descending colon and sigmoid colon, the rectum and superior part of the anal
canal….as well as the urinary bladder and most of the urethra.
o The expanded terminal part of the hindgut, the cloaca, is an endoderm-lined
chamber that is in contact with the surface ectoderm at the cloacal
membrane. This membrane is composed of endoderm of the cloaca and
ectoderm of the proctodeum or anal pit. The cloaca receives the allantois
ventrally, which is a fingerlike diverticulum.
o The cloaca is divided into dorsal and ventral parts by a wedge of
mesenchyme called the urorectal septum, that develops in the angle between
the allantois and hindgut. Two sets of fold come together to form the
urorectal septum. The rectum and cranial part of the anal canal form
dorsally.
o Where the urorectal septum fuses with the cloacal membrane becomes the
perineal body, the center of the perineum
o Mesenchymal proliferations produce elevations of the surface ectoderm
around the anal membrane. This membrane becomes a depression called the
proctodeum or anal pit. A membrane separates the external anus from the
anal canal until the 8th week.
o Errors in Hindgut Formation
 Persistent cloaca can form, results in the anus, urethra and potentially
the vagina open into a common sac.
 Anal stenosis can occur resulting in a narrowed anal opening.
 Persistent anal membrane can occur.
 Anoperineal fistula can occur, which results in incontinence issues.
 Rectovaginal fistula can form, no anal canal at all.
 Rectouretral fistula can form resulting in feces passing through
urethra.
 Rectal atresia results in a blind ended pouch, anal canal and rectum
never meet.
 Atresia can also result in anal canal formation and connection to
rectum, but result in a part in the middle dying off leaving them
disconnected.
 Hirschsprung’s disease
 Neural crest cells never migrate to the gut, resulting in an
aganglionic area of intestine that is tonically contracted.
 The intestine proximal to the aganglionic intestine becomes
packed with feces, creating a megacolon. The aganglionic
colon must be resected to correct the disorder.
 Occurs in 1 in 5000 births.
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Lecture 7-Large Intestine to Rectum (Hindgut)
 Hindgut is the terminal part of the GI tract. Transition from midgut is along the
transverse colon, typically thought of as the distal 1/3 of the transverse colon,
descending colon, sigmoid colon and upper 1/3 of rectum.
 Same features seen on the midgut are seen on the hindgut colon
o Features of the large bowel include
 Longitudinal muscles called the tenia coli
 External bulges called haustra
 Fatty globs known as appendices epiploicae
 Internally, ridges known as plicae semilunares.
 3 named tenia coli: omental tenia coli, free tenia coli, and mesocolic tenia coli.
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Paracolic Gutters
o Ascending and descending parts of the large intestine and secondarily
retroperitoneal. Lateral to each is a space that allows free flow from top to
bottom of the peritoneal cavity.
Arterial Supply
o Most hindgut arterial supply is from branches of the inferior mesenteric
artery.
o Anastomosis with SMA via marginal artery, with internal iliac artery via
middle rectal artery.
o Venous drainage
 As with the rest of the GI tract, the drainage is via venae comitantes
that drain into portal system.
Mesentery of Hindgut
o Entire colon is originally suspended from the mesentery.
o The ascending and descending parts of the colon become retroperitoneal
they lose their ‘mesocolon.’ This leaves the cecum freely mobile.
Innervation
o Sympathetic innervation of the hindgut is from lumbar splanchnic nerves and
the superior hypogastric plexus.
 Synapsing takes place at ganglia around the IMA, postysnaptics travel
with arterial branches.
o Parasympathetics
 Only parasympathetics not associated with a cranial nerve.
 S2-S4 ventral rami
 Parasympathetics travels through spinal cord to these levels then
exits to innervate distal colon and pelvic organs (except gonads).
 These are pre-ganglionic fibers, they synapse in the wall of the organ
innervated.



Gonads, both male and female, have vagus parasympathetic
innervation
Lymphatics
o As in all GI tract, lymphatics are found associated with arterial supply and
drain back to nodes along the aorta, then the lumbar trunks and/or cisterna
chylii
Clinical Notes
o Lots of cell turnover in the GI tract.
o Lots of muscular action required to move digesting/digested matter along.
o Diverticulosis-formation of outpouchings in the wall of the colon, can occur
anywhere along the GI tract.
 Pockets can become filled with infection from stool. Leads to
inflammation and possibly rupture of bowel wall, which leads to
infection spreading to peritoneal space or retroperitoneal space.
 Leads to peritonitis!
o Any place that has rapid, frequent mitotic activity is prone to inappropriate
cell replication. Can result in colon polyps and are the result of inappropriate
replication.
 Polyps are removed during colonoscopy. If they aren’t removed they
can develop into cancer.
o Colon is a common place for cancer to develop.
o Potential porta-caval anastomoses in the hindgut include the descending
colon and the rectum.
 Descending colon is secondarily retroperitoneal
 Rectum has overlap via superior and middle rectal veins