Structures of the Foregut
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Structures of the Foregut
The gastrointestinal tract can be divided into three parts; foregut, midgut and hindgut. This terminology
relates to its embryological development. During this session you will gain an overview of these 3 regions
and study the structures of the foregut in detail.
1. Overview of the Primitive Gut Derivatives
The gastrointestinal tract is divided into the foregut, midgut and hindgut, which relates to its embryonic
development from the primitive gut tube. The arterial blood supply to the gastrointestinal tract is
supplied by 3 main branches of the abdominal aorta. The organs of each region of the gut are supplied
by a common branch. Complete the table below to summarise this information.
Structures Blood su lForegut Pharynx, esophagus, stomach,
proximal half of duodenum
Artery: Celiac trunk (branches from the abdominalaorta at the upper border of vertebra LI)
Vein: Hepatic portal vein
Midgut Distal half of duodenum; jejunum,
ileum, cecum, appendix, ascending
colon, proximal (right) two-thirds of
transverse colon
Artery: Superior mesenteric artery (arises from the
abdominal aorta at the lower border of vertebra LI)
Vein: Inferior mesenteric vein
Hindgut Distal (left) one-third of transverse
colon; descending colon, sigmoid
colon, rectum, superior portion of
anal canal
Artery: Inferior mesenteric artery (which branches
from the abdominal aorta at approximately vertebral
level LIII)
Vein: Superior mesenteric vein
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2. Anatomy of foregut structures
The foregut extends from the lower part of the oesophagus to the 2nd
part of the duodenum; it
includes the liver, pancreas and spleen. Today we will study the structures of the foregut (excluding the
oesophagus, liver, gall bladder and spleen which will be studied later). For convenience we will
examine the whole of the duodenum. Examine the prosections showing the organs in-situ and themodels and isolated specimens.
Abdominal wall
Review the muscles of the abdominal wall. Identify the falciform ligament as it extends between the liver
and the anterior abdominal wall. The ligamentum teres should be seen in the free inferior border of the
falciform ligament. What is the ligamentum teres?
Visceral surface of the liver. A. Illustration
The ligamentum
teres is the
obliterated fibrous
remnant of the left
umbilical vein of
the fetus. It
originates at the
umbilicus. It passes
superiorly in the
free margin of the
falciform ligament.
From the inferior
margin of the liver,
it may join the left
branch of the
portal vein or it
may be incontinuity with the
li amentum
The falciform
ligamentis a ligament
that attaches
theliver to the anterior
body wall. It is a broad
and thin antero-
posterior peritoneal
fold, falciform (Latin
"sickle-shaped"), its
base being directed
downward and
backward and its apex
upward and backward.
The falciform ligament
droops down from
thehilum of the liver.
http://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Hilum_(anatomy)http://en.wikipedia.org/wiki/Hilum_(anatomy)http://en.wikipedia.org/wiki/Liver -
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Abdominal organs in-situ
Note the greater omentum. How extensive is it in your prosection?
Is there any evidence of the greater omentum having walled offareas of infection?
Stomach
In which abdominal region/s is the stomach located?
Left hypogastrium, Epigastrium and Umbilical
Where do the lesser and greater omentum attach to the stomach?
Greater omentum
Peritoneal fold suspended from the greater curvature of the stomach
Lesser omentum
Joins the lesser curvature of the stomach
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Identify the cardia, fundus, body, pylorus (antrum, canal & sphincter) and the greater and lesser
curvatures. Feel and comment on the pyloric and cardiac sphincters.
Examine the rugae. What is their function?
Internally, the stomach lining is composed of numerous gastric folds, or rugae. These gastric folds, which
are observed only when the stomach is empty, allow the stomach to expand greatly when it fills and then
return to its normal J-shape when it empties.
Where does lymph from the stomach drain to?
The lymph vessels follow the artery into the left gastric node
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Draw a simple diagram showing the blood supply of the stomach. Can you find any of the
branches on the specimen?
Blood supply to the stomach
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Duodenum
Examine the first part of the duodenum that extends from the pyloric region of the stomach. This
part is suspended from the liver by the hepatoduodenal ligament and is intraperitoneal.
The remainder of the duodenum is retroperitoneal.
Peritoneal Relations
It is retroperitoneal and fixed. Its anterior surface is covered with peritoneum, except in the median
plane where it is crossed by superior mesenteric vessels and by the root of the mesentery.
Name and identify the four parts of the duodenum and state the artery that supplies each
part.
1._Superior part, extends from the pyloric orifice of the stomach to the neck of the gallbladder, is
just right of the body of vertebra L1 and passes anteriorly to the bile duct, gastroduodenal artery,
portal vein and inferior vena cava
-- supplied by branches derived from the celiac trunk (hepatic, right gastric supraduodenal, right
gastoepiploic and superior panreatico-duodenal arteries)
2. Descending part, to the right of midline, its anterior surface is crossed by the transverse colon,posterior to it is the right kidney and medial to it is the head of the pancreas contains major
duodenal papilla which is the common entrance for bile and pancreatic ducts and minor duodenal
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papilla which is the entrance for the accessory pancreatic duct-- The upper part (supplied by branches derived from the celiac trunk (hepatic, right gastricsupraduodenal, right gastoepiploic and superior panreatico-duodenal arteries))
3. Horizontal part; begins at duodenal flexure where it is crossed by the superior mesenteric
vessels and by the root of the mesentery-- Inferior pancreaticoduodenal branch of the superior mesenteric artery
4. Ascending part; passes upward or to let of aorta to approximately the upper border of vertebra
L11 and terminates at the duodenojejunal flexure-- Inferior pancreaticoduodenal branch of the superior mesenteric artery
On the internal aspect of the duodenum find the minor and major duodenal papillae. What
opens into the duodenum at each of these sites?
Minor duodenal papilla
Accessory pancreatic duct
Major duodenal papilla
Bile and pancreatic duct
Note the arrangement and distribution of the plicae circulares. What is their function?
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Unlike the folds in thestomach,they are permanent, and are not obliterated when theintestine is
distended.
The space between circular folds are smaller than thehaustra of thecolon,and, in contrast to
haustra, circular folds reach around the whole circumference of the intestine. These differences can
assist in distinguishing the small intestine from the colon on anabdominal x-ray.
Distribution
They are not found at the commencement of theduodenum,but begin to appear about 2.5 or 5 cm.
beyond thepylorus.
In the lower part of the descending portion, below the point where thebile andpancreatic
ducts enter the small intestine, they are very large and closely approximated.
In the horizontal and ascending portions of the duodenum and upper half of thejejunum they are
large and numerous, but from this point, down to the middle of the ileum, they diminishconsiderably in size.
In the lower part of theileum they almost entirely disappear; hence the comparative thinness of this
portion of the intestine, as compared with the duodenum and jejunum.
Function
The circular folds slow the passage of thefood along the intestines, and afford an increased surface
forabsorption.They are covered with small fingerlike projections calledvilli (singular, villus). Each
villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from thechyme.
http://en.wikipedia.org/wiki/Stomachhttp://en.wikipedia.org/wiki/Intestinehttp://en.wikipedia.org/wiki/Haustrahttp://en.wikipedia.org/wiki/Colon_(anatomy)http://en.wikipedia.org/wiki/Abdominal_x-rayhttp://en.wikipedia.org/wiki/Duodenumhttp://en.wikipedia.org/wiki/Pylorushttp://en.wikipedia.org/wiki/Bile_ducthttp://en.wikipedia.org/wiki/Pancreatic_ducthttp://en.wikipedia.org/wiki/Pancreatic_ducthttp://en.wikipedia.org/wiki/Jejunumhttp://en.wikipedia.org/wiki/Ileumhttp://en.wikipedia.org/wiki/Foodhttp://en.wikipedia.org/wiki/Digestionhttp://en.wikipedia.org/wiki/Intestinal_villihttp://en.wikipedia.org/wiki/Chymehttp://en.wikipedia.org/wiki/Chymehttp://en.wikipedia.org/wiki/Intestinal_villihttp://en.wikipedia.org/wiki/Digestionhttp://en.wikipedia.org/wiki/Foodhttp://en.wikipedia.org/wiki/Ileumhttp://en.wikipedia.org/wiki/Jejunumhttp://en.wikipedia.org/wiki/Pancreatic_ducthttp://en.wikipedia.org/wiki/Pancreatic_ducthttp://en.wikipedia.org/wiki/Bile_ducthttp://en.wikipedia.org/wiki/Pylorushttp://en.wikipedia.org/wiki/Duodenumhttp://en.wikipedia.org/wiki/Abdominal_x-rayhttp://en.wikipedia.org/wiki/Colon_(anatomy)http://en.wikipedia.org/wiki/Haustrahttp://en.wikipedia.org/wiki/Intestinehttp://en.wikipedia.org/wiki/Stomach -
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Pancreas
Is the pancreas an intraperitoneal or retroperitoneal organ?
Retroperitoneal
Examine the specimen to determine the relations of the pancreas.
Anterior
Stomach and duodenum
Posterior
Ucinate process, left kidney, Aorta and Vena Cava
Identify the head, neck, body and tail of the pancreas. Note that the head of the pancreas lies
in the curve of the duodenum and its tail extends towards the spleen.
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Find the main and accessory pancreatic ducts. What part of the pancreas is drained by the duct
system?
The simple cuboidal epithelial cells lining the pancreatic ducts secrete bicarbonate (alkaline fluid) to
help neutralize the acidic chyme arriving in the duodenum from the stomach. Most of the pancreatic
juice travels through ducts that merge to form the main pancreaticduct, which drains into themajor duodenal papilla in the duodenum.
A smaller accessory pancreatic duct drains a small amount of pancreatic juice into a minor duodenal
papilla in the duodenum
.
Where are the endocrine cells of the pancreas located?
Scattered amongst the pancreatic acini are small clusters of cells called pancreatic islets (islets of
Langerhans). They number in millions but forms only 1% of the pancreatic volume.
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Which vessels provide the blood supply to the pancreas?
The arterial supply to the pancreas (Fig. 4.101) includes the:
gastroduodenal artery from the common hepatic artery (a branch of the celiac trunk);
anterior superior pancreaticoduodenal artery from the gastroduodenal artery; posterior superior pancreaticoduodenal artery from the gastroduodenal artery;
dorsal pancreatic artery from the inferior pancreatic artery (a branch of the splenic artery);
great pancreatic artery from the inferior pancreatic artery (a branch of the splenic artery);
dorsal pancreatic and greater pancreatic arteries (branches of the splenic artery);
anterior inferior pancreaticoduodenal artery from the inferior pancreaticoduodenal artery (a
branch of the superior mesenteric artery); and
posterior inferior pancreaticoduodenal artery from the inferior pancreaticoduodenal artery
(a branch of the superior mesenteric artery).