SI DUODENUM

Overview of the Small Intestine

• The small intestine is the longest part of the alimentary canal, extending from the pylorus of the stomach to the ileocecal junction. It is crucial for digestion and absorption of nutrients.

• The small intestine is divided into three parts:

  • Duodenum

  • Jejunum

  • Ileum

Duodenum Characteristics

• The duodenum is a C-shaped tube approximately 10 in. (25 cm) long, connecting the stomach to the jejunum.

• It serves as the site for the openings of the bile and pancreatic ducts and curves around the head of the pancreas.

• Covering: The first inch (2.5 cm) resembles the stomach, with both anterior and posterior surfaces covered in peritoneum.

• It features the lesser omentum attached to its upper border and the greater omentum to its lower border. The lesser sac lies behind this short segment, while the rest of the duodenum is retroperitoneal.

Page 2: Duodenum Parts and Relations

First Part of the Duodenum

• Begins at the pylorus, running upward and backward on the transpyloric plane, at the level of the first lumbar vertebra.

• Relations:

  • Anteriorly: Quadrate lobe of the liver and gallbladder

  • Posteriorly: Lesser sac (first inch), gastroduodenal artery, bile duct, portal vein, inferior vena cava

  • Superiorly: Entrance into the lesser sac (epiploic foramen)

  • Inferiorly: Head of the pancreas

Second Part of the Duodenum

• Runs vertically downward in front of the hilum of the right kidney, along the second and third lumbar vertebrae.

• The bile duct and main pancreatic duct pierce the medial wall, forming the ampulla that opens at the major duodenal papilla.

• Relations:

  • Anteriorly: Fundus of the gallbladder, right lobe of the liver, transverse colon, coils of the small intestine

  • Posteriorly: Hilum of the right kidney and right ureter

  • Laterally: Ascending colon, right colic flexure, right lobe of the liver

  • Medially: Head of the pancreas, bile duct, and main pancreatic duct

Third Part of the Duodenum

• Runs horizontally to the left on the subcostal plane, passing in front of the vertebral column.

• Relations:

  • Anteriorly: Root of the mesentery of the small intestine, superior mesenteric vessels, coils of the jejunum

  • Posteriorly: Right ureter, right psoas muscle, inferior vena cava, aorta

  • Superiorly: Head of the pancreas

  • Inferiorly: Coils of the jejunum

Fourth Part of the Duodenum

• Runs upward and to the left towards the duodenojejunal flexure.

• Held in position by the ligament of Treitz (suspensory ligament of the duodenum).

• Relations:

  • Anteriorly: Beginning of the root of the mesentery, coils of jejunum

  • Posteriorly: Left margin of the aorta, medial border of the left psoas muscle

Page 3: Mucous Membrane, Blood Supply and Nerve Supply of the Duodenum

Mucous Membrane of the Duodenum

• The mucous membrane is mostly thick and smooth in the first part of the duodenum. In the remaining parts, it is thrown into circular folds known as plicae circulares.

• The major duodenal papilla located where the bile duct and main pancreatic duct pierce the medial wall of the second part is surrounded by smooth mucosa, while a smaller papilla may open higher up for the accessory pancreatic duct.

Blood Supply

• Upper half supply: Superior pancreaticoduodenal artery (from gastroduodenal artery)

• Lower half supply: Inferior pancreaticoduodenal artery (from the superior mesenteric artery)

• Venous drainage:

  • Superior pancreaticoduodenal vein drains into the portal vein.

  • Inferior pancreaticoduodenal vein joins the superior mesenteric vein.

Lymph Drainage

• Lymphatic vessels follow the arterial supply:

  • Upper duodenum drains via pancreaticoduodenal nodes to gastroduodenal nodes and then to celiac nodes.

  • Lower duodenum drains via pancreaticoduodenal nodes to superior mesenteric nodes around the origin of the superior mesenteric artery.

Nerve Supply

• Supplied by sympathetic and parasympathetic (vagus) nerves, derived from the celiac and superior mesenteric plexuses.