THE DUODENUM

DEVELOPMENT:

· Duodenum is the dividing point between the foregut and midgut.

· It forms in response to the rotation of the stomach.

LOCATION:

· It is retroperitoneal. (The first portion is actually intra - peritoneal, but we won’t count that).

· Umbilical Region and Medial parts of the Left and Right upper quadrants.

EXTERNAL MORPHOLOGY: It is a C-Shaped portion of the gut.

• Duodenal Bulb (I) (foregut) (at about the level of LV1 -- the transpyloric plane)
1. Hepatoduodenal Ligament: There is a ligament which is part of lesser omentum.
2. This ligament is the sign of peritoneum surrounding the duodenum; hence we will consider the whole duodenum as retro- peritoneal.

• Descending Duodenum (II) (foregut) (LV2)
• Horizontal Duodenum (III) (midgut) (LV3)
• Ascending Duodenum (IV) (midgut) (LV2-3)

1. Ligament of Treitz: Attaches the fourth part of the duodenum to the right crus of the diaphragm. It goes posterior to the pancreas. Essentially attaches duodenum to posterior wall.
2. It is the Suspensory Muscle of the Duodenum -- function to hold duodenum opened / closed for passage of food into Jejunum.

INTERNAL MORPHOLOGY:

• Duodenal Bulb is smooth internally, while the rest of it is rough with mucosal folds.
• Plicae Circulares: The name of the folds on the distal three parts of duodenum.
• Hepato-pancreatic Duct: Anastomose of the common bile duct and pancreatic duct onto the duodenum. It joins at the second part of the duodenum.
• Major Papilla: The opening into the common bile and pancreatic ducts.
• The pancreatic duct usually joins the common bile duct before it reaches the major papilla.
• Minor Papilla: Another duct opening.
• Ampulla (of Vater): Ductule right at the major papilla, which holds bile and pancreatic enzymes.

RELATIONSHIPS:

o The pancreas lies in the internal curvature of the C-Shape.

o Duodenal bulb is in transpyloric plane.

o Superior Mesenteric Artery usually passes over the horizontal duodenum.

o Renal Artery and Vein passes posterior to the ascending (fourth part of) duodenum.

o Aorta: The fourth part of the duodenum lies on the Aorta. Aorta is posterior to duodenum.

o Transverse Mesocolon: Inferior aspect of transverse colon. It covers the pancreas, and crosses the duodenum at the fourth part (ascending, and most medial part).

o Portal Triad: Common Bile Duct, Portal Vein, Proper Hepatic Artery.

• They are located posterior to the duodenal bulb.
• They are within the free edge of the lesser omentum (hepatoduodenal ligament).

o Pancreas: Within the C-Shape of the duodenum. The head of the pancreas lies posterior to the descending and horizontal duodenum.

CLINICAL CONSIDERATIONS:

o Duodenal Atresia: Lack of development of duodenum.

o Duodenal Stenosis: Clogging of duodenum.

o Vomiting: Look for bile as a sign of where the obstruction occurred. If there is bile, then it was the lower duodenum (distal to duodenal papilla), if not, then it was the proximal duodenum (proximal to papilla).

o Duodenal Ulcer: Posterior aspect of the duodenal bulb, if the wall is broken, hemorrhaging can occur as it invades the gastroduodenal artery.

§ Four times more prevalent than peptic ulcers.

o Para duodenal Hernia: The Para duodenal Recess lies just posterior to the fourth part of the duodenum. A portion of duodenum and ileum can herniate there.

§ The inferior mesenteric vein is right there, and can be ruptured as a result.

o Enterogastrone: Is released by duodenum to decrease the peristalsis and acidity of material coming from stomach.

o Cholecystitis: Inflammation of gall-bladder, where bile is stored. Duodenum can form adhesions, etc., from what was originally cholecystitis.

o Referred Pain: Pain referred in duodenum is generally referred to umbilical region, through the greater thoracic splanchnic nerve.

VASCULAR / LYMPH SUPPLY:

§ Supplied by both the Celiac Artery (foregut parts) and Superior Mesenteric Artery (Midgut parts).

§ Gastroduodenal Arteries: Come from the celiac trunk ultimately.

o Celiac Trunk ------> Common Hepatic ------> Gastroduodenal.

§ Hepatic Arteries: Proper Hepatic and Left Hepatic come off of the Common Hepatic Artery.

§ Superior Mesenteric Artery and Vein passes over last half (midgut portions) of the duodenum.

Category: Anatomy Notes