Download 27-As of Mid& hindgut

Superior Mesenteric
Artery
It supplies the distal part of the
duodenum; jejunum; ileum;
cecum; appendix; ascending
colon and most of the transverse
colon.
It arise from the front of the
abdominal aorta just below the
celiac artery ( 1cm) opposite L1.
It runs downward and to the right
behind the neck of the pancreas
( where it arises ) and in front of
the third part of the duodenum.
It continues downward to the
right between the layers of the
mesentery of the small intestine
It ends in the right iliac fossa by
anastomosing with the ileal
branch of its own ileocolic
branch.
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Branches:
1- Inferior pancreaticoduodenal artery
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It passes to the right as a single or
double branch along the upper border
of the third part of the duodenum then
between the head of the pancreas and
the 2nd part of the duodenum. It
supplies the head of the pancreas and
the adjoining part of the duodenum.
2- Middle colic artery
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It runs forward in the transverse
mesocolon to supply the transverse
colon and divides into right which
anastomose with ascending branch of
the right colic artery & left branches
which anastomose with superior
(ascending) left colic artery.
3- Right colic artery
It is often a branch of the ileocolic
artery. It passes to the right to supply
the ascending colon and divides into
ascending and descending branches.
4- ILeocolic artery
It passes downward and to the
right.
It gives rise to a superior
( ascending ) branch that
anastomoses with the
descending branch of the right
colic artery and an inferior
( descending ) branch that gives
rise to the ileal branch which
anastomoses with the end of the
superior mesenteric artery.
also, the inferior branch gives
rise to anterior and posterior
cecal arteries.
The appendicular artery is a
branch of the posterior cecal
artery.
5- Jejunal and Ileal branches
They are distributed to the jejunum and ileum except terminal part of the ileum
which is supplied by the ileocolic artery. They are 12 to 15 in number and arise
from the left side of the superior mesenteric artery. They run parallel with one
another between the layers of the mesentery.
Each artery divides into 2 vessels which unite with adjacent branches to form
a series of arcades. Branches from the arcades divide and unite to form 2nd; 3rd
and 4th series of arcades.
In the jejunum one set of arches exists.
But in the ileum 4 or 5 series are
present.
From the terminal arcades, small
straight vessels supply the intestine.
These straight terminals vessels are
called vasa recta.
They are distributed to opposite
surfaces of the small intestine and the
neighbouring vessels do not
anastomose with one another.
So , those vasa recta are end-arteries.
Observe that the arterial arcades in the
ileum are more complex than the
jejunum and the vasa recta are shorter
in the ileum than in the jejunum.
Inferior Mesenteric Artery
It supplies the distal part of the transverse
colon; the left colic flexure; the descending
colon; the sigmoid colon; the rectum and the
upper part of the anal canal.
It arises from front of the abdominal aorta
about 1.5 inch ( 3.8 ) above its bifurcation or
opposite L3 vertebra.
It lies behind the 3 rd part of the duodenum. It
lies medial to the inferior mesenteric vein. It
lies lateral to aorta.
It runs downward and to the left and crosses
the left common iliac artery. Here, it becomes
the superior rectal artery
Branches
1- Left colic artery
It divides into ascending branch which runs
upward and to the left and supplies the distal
third of the transverse colon & the left colic
flexure. The descending branch supplies the
descendeing colon & anastomoses with
sigmoid branch.
2- Sigmoid arteries
They are 2 or 3 in number which
anastomose with each other and supply the
descending and sigmoid colon. It anastomose
inferiorly with superior rectal artery.
3- Superior rectal artery
It is a continuation ( termination ) of the
inferior mesenteric artery. It crosses the left
common iliac artery. It descends into the
pelvis behind the rectum.
It supplies the rectum and upper half of the
anal canal and anastomoses with the middle
rectal and inferior rectal arteries.
Marginal artery
The anastomosis of the colic arteries around
the concave margin of the large intestine
forms a single arterial trunk called the
marginal artery.
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It begins at the ileocecal junction where it
anastomoses with the ileal branches of the
superior mesenteric artery. It ends by
anastomosing freely with the superior rectal A.
Venous Drainage
The venous blood from the greater part
of the G.I.T. and its accessory organs
drains to the liver by the portal venous
system.
The proximal tributaries drain directly
into the portal vein. But the veins
forming the distal tributaries
correspond to the branches of the
celiac artery and the superior & inferior
mesenteric arteries.
Portal Vein
It drains blood from the lower third of
the esophagus to halfway down the
anal canal. It also, drains blood from
the spleen; pancreas; and gallbladder.
It enters the liver and breaks up into
sinusoids, from which blood passes
into the hepatic veins that join the
inferior vena cava.
It is about 2 inch ( 5 cm ) long.
It is formed behind the neck of the pancreas by the union of the superior mesenteric and
splenic veins.
It ascends to the right, behind the first part of the duodenum and enters the lesser
omentum.
It then runs upward in front of the opening into the lesser sac to the porta hepatis where it
divides into right and left terminal branches.
The portal circulation begins as a capillary plexus in the organs it drains and ends by
emptying its blood into sinusoids within the liver.
Relations of the portal vein in the lesser omentum
At the free border of lesser omentum the hepatic artery and bile duct lie anteriorly and
portal vein lie posteriorly.
Tributaries of the Portal Vein
1- Splenic vein
It leaves the hilum of the spleen and passes
to the right in the splenicorenal ligament lying
below the splenic artery behind the posterior
surface of the body of the pancreas..
It unites with the superior mesenteric vein
behind the neck of the pancreas to form the
portal vein.
It receives ( its tributaries ) the short
gastric; left gastroepiploic; inferior mesenteric
and pancreatic veins.
2- Inferior mesenteric vein
It ascends on the posterior abdominal wall
and joins the splenic vein behind the body of
the pancreas.
It receives the superior rectal veins. The
sigmoid veins and the left colic vein.
3- Superior mesenteric vein
It ascends in the root of the mesentery of the
small intestine on the right side of the artery.
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It passes in front of the third part of the
duodenum and joins the splenic vein behind the
neck of the pancreas.
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4
It receives the jejunal; ileal; ileocolic; right;
middle colic; inferior pancreaticoduodenal and
right gastroepiploic veins.
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4- Left gastric vein
It drains the left portion of the lesser curvature
of the stomach and the distal part of the
esophagus. It opens directly into the portal vein.
5- Right gastric vein
It drains the right portion of the lesser
curvature of the stomach and drains directly into
the portal vein.
6- Cystic vein
These veins either drain the gallbladder
directly into the liver or join the portal vein.
Portal- Systemic Anastomoses
Under normal conditions, the portal
venous blood traverse the liver and
drains into the inferior vena cava of the
systemic venous circulation by way of
the hepatic veins.
This is the direct route, however, other
smaller communications exist between
the portal and systemic systems and
they become important when the direct
route becomes blocked.
These communication are as the follows
1- At the lower third of the esophagus, the
esophageal branches of the left gastric
vein ( portal tributary ) anastomose
with the esophageal veins draining the
middle third of the esophagus into the
azygos veins ( systemic tributary ). It
gives rise to esophageal varices.
2- Halfway down the anal canal, the
superior rectal veins ( portal
circulation ) draining the upper half of
the anal canal anastomose with the
middle & inferior rectal veins
( systemic tributaries ) which are
tributaries of the internal iliac and
internal pudendal veins respectively. It
gives rise to Piles.
3- The paraumbilical veins connects the
left branch of the portal vein with the
superficial veins of the anterior
abdominal wall (systemic tributaries)
The paraumbilical veins travel in the
falciform ligament and accompany the
ligamentum teres. It gives rise to Caput
medusae.
4- the veins of the ascending colon;
descending colon; duodenum;
pancreas and liver (portal tributary)
anastomose with the renal; lumbar and
phrenic veins ( systemic tributaries ).
Portal Vein Obstruction
In these cases which may be due to
cirrhosis of the liver capillaries
connecting the portal and systemic
venous circulations open up and
become dilated and tortuous and
may lead to haemorrahge.
The superficial veins around the
umbilicus and the paraumbilical
veins become distended.
These distended subcutaneous
veins radiate out from the umbilicus
producing in sever cases the
clinical picture referred to as caput
medusae.
The lateral thoracic vein & the
superficial epigastric vein and
lumbar are systemic veins.
Portal Hypertension
It is a common clinical condition.
Enlargement of the portal –systemic
connections is accompanied by
congestive enlargement of the
spleen.
Portocaval shunts for the treatment
of the portal hypertension may
involve the anstomosis of the portal
vein, because it lies within the lesser
omentum and to the anterior wall of
the inferior vena cava behind the
entrance into the lesser sac.
The splenic vein may be
anastomosed to the left renal vein
after removing the spleen.