Structures of the Foregut

8/13/2019 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).

Structures of the Foregut

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