49. GA - Anatomy of the Duodenum, Pancreas, & Spleen

Duodenum

• The duodenum is the first part of the small intestine responsible for digestion and absorption of chyme.
• It receives bile from the liver and enzymes from the pancreas.
• The duodenum is approximately 25 cm long and mostly a retroperitoneal structure.
• It courses around the head of the pancreas on the right side, crosses the inferior vena cava (IVC) and aorta to the left side, and transitions into the jejunum at the duodeno-jejunal flexure.
• The superior duodenal fold and recess, inferior duodenal fold and recess, paraduodenal fold and recess, and retroduodenal recess are important anatomical features of the duodenum.
• The duodenum receives blood supply from the gastroduodenal and inferior pancreaticoduodenal arteries.
• The proximal half of the duodenum is supplied by the gastroduodenal artery, and the distal half by the inferior pancreaticoduodenal artery.
• Superior and inferior pancreaticoduodenal arteries anastomose in the head of the pancreas forming anterior and posterior pancreaticoduodenal arterial arcades.
• The first part of the duodenum receives blood supply from the supraduodenal artery, which branches off from the celiac trunk.
• Venous drainage of the duodenum occurs via the superior mesenteric and right gastric veins, draining into the hepatic portal venous system.
• Lymphatics of the duodenum drain into pancreaticoduodenal nodes, pyloric nodes, and superior mesenteric nodes.

Pancreas

• The pancreas is a digestive/endocrine gland located in the posterior abdominal wall.
• It is mostly retroperitoneal, lying posterior to the omental bursa, and traverses between the levels of LV1-LV3.
• The pancreas serves as both an exocrine gland secreting digestive enzymes (trypsin, chymotrypsin, amylase, lipase) and an endocrine gland releasing hormones (insulin, glucagon).
• The pancreas is divided into the head, neck, body, and tail.
• The head of the pancreas encircles the superior mesenteric artery and vein on the right side, terminating as a wedge-shaped extension called the uncinate process.
• The main pancreatic duct, beginning at the tail, runs through the pancreas, receiving tributaries from the tail, body, neck, uncinate process, and part of the head of the pancreas.
• The main pancreatic duct unites with the bile duct to form the hepatopancreatic ampulla, which opens into the descending part of the duodenum via the major duodenal papilla.
• The flow of bile and pancreatic juice into the hepatopancreatic ampulla is regulated by the sphincter of the common bile duct, which surrounds the terminal part of the bile duct.
• Flow from the hepatopancreatic ampulla into the duodenum is controlled by the hepatopancreatic sphincter.
• The accessory pancreatic duct drains part of the head of the pancreas and may connect to the main pancreatic duct or remain patent, emptying into the duodenum via the minor duodenal papilla.
• The pancreas receives blood supply from branches of the celiac and superior mesenteric arteries.
• Venous drainage of the pancreas occurs via the splenic vein and superior mesenteric vein, draining into the portal vein.
• Lymphatic drainage of the pancreas occurs via pancreaticoduodenal, pyloric, and superior mesenteric nodes.

Spleen

• The spleen is a non-digestive organ located in the left hypochondrium, posterior to the stomach.
• It is a soft, highly vascular, and fragile organ that plays a role in immune function and blood filtration.
• The spleen has a hilum where vessels enter and exit.
• The spleen is covered by visceral peritoneum except for its hilum.
• The spleen receives its blood supply from the splenic artery, a branch of the celiac trunk.
• Venous drainage occurs via the splenic vein, which joins with the superior mesenteric vein to form the portal vein.
• Lymphatics of the spleen drain into splenic nodes around the hilum.
• Innervation of the spleen is provided by the celiac plexus.
• A ruptured spleen is life-threatening, leading to severe intraperitoneal hemorrhage and shock.
• Splenomegaly, or enlargement of the spleen, can crowd other abdominal viscera, causing pain and discomfort.
• Removal of the spleen, splenectomy, can be performed without significant health issues in adults.
• Splenic artery branches do not anastomose, so obstruction of a branch can lead to necrosis of the affected splenic tissue.

Divisions of the Duodenum

• The duodenum is divided into four parts: superior, descending, transverse, and ascending.
• The superior part is the most movable and is further divided into proximal and distal regions.
• The proximal superior duodenum is smooth and called the duodenal ampulla, cap, or bulb.
• The distal superior duodenum has corrugated folds and transitions to being retroperitoneal.

Superior Part Anatomical Relationships

• Anterior: peritoneal cavity, gallbladder, quadrate lobe of the liver.
• Posterior: bile duct, portal vein, inferior vena cava, gastroduodenal artery.
• Superior: neck of the gallbladder.

Descending Part Anatomical Relationships

• Anterior: peritoneal cavity, transverse colon, right colic flexure, ascending colon.
• Posterior: right psoas major, inferior vena cava, aorta, right ureter.
• Superior: head of the pancreas, superior mesenteric vessels.

Transverse Part Anatomical Relationships

• Anterior: small bowel, transverse colon.
• Posterior: right psoas major, inferior vena cava, aorta, right ureter.
• Superior: head of the pancreas, superior mesenteric vessels.

Ascending Part Anatomical Relationships

• Anterior: beginning of the root of the mesentery, coils of the jejunum.
• Posterior: left psoas major muscle, left margin of the aorta.
• Medial: head of the pancreas, superior mesenteric artery and vein.
• Superior: body of the pancreas.

Peritoneal Recesses

• The duodenum has several peritoneal folds and recesses, mainly in the area where the ascending duodenum transitions to the jejunum.
• These include the superior and inferior duodenal folds and recesses, the paraduodenal fold and recess, and the retroduodenal recess.

Arterial Supply

• The duodenum is supplied by the gastroduodenal and inferior pancreaticoduodenal arteries, which anastomose to form arterial arcades.
• The proximal half is supplied by the gastroduodenal artery, and the distal half by the inferior pancreaticoduodenal artery.
• The first part of the duodenum is supplied by the supraduodenal artery, which can arise from different branches.

Venous Drainage

• Venous drainage generally follows the arteries and drains into the hepatic portal venous system via the superior mesenteric and right gastric veins.

Lymphatics

• The duodenum drains into pancreaticoduodenal nodes, pyloric nodes, and other lymph nodes.

Pancreas Anatomy

• The pancreas is divided into four regions: head, neck, body, and tail.
• The head of the pancreas is surrounded by the duodenum and is the largest part.
• The neck is retroperitoneal and located between the head and body.
• The body is retroperitoneal and runs between vertebral levels LV1 to LV3, crossing the aorta.
• The tail is a short peritoneal structure suspended within the splenorenal ligament.

Pancreatic Ducts

• The pancreas contains a main pancreatic duct and an accessory pancreatic duct.
• The main pancreatic duct joins the common bile duct to form the hepatopancreatic ampulla.
• The ampulla opens into the duodenum at the major duodenal papilla.

Clinical Significance of the Pancreas

• Gallstone blockage in the hepatopancreatic ampulla can cause pancreatitis.
• Obstruction of the bile duct in pancreatic cancer can cause obstructive jaundice.
• Surgical removal of pancreatic tumors often involves resection of parts of the duodenum and other parts of the GI tract.

Spleen Anatomy

• The spleen is a large, highly vascular lymphatic organ located in the left upper quadrant of the abdomen.
• It is a peritoneal structure suspended off of the posterior abdominal wall by the splenorenal ligament and attached to the stomach by the gastrosplenic ligament.
• It has a visceral surface with the hilum and impressions from neighboring organs, and a smooth diaphragmatic surface.

Spleen Functions

• The spleen filters blood and removes old or damaged red blood cells.
• It stores white blood cells and plays a role in immune function.
• It is involved in red blood cell production in the fetus.

Explore the anatomy and functions of the duodenum, the first section of the small intestine. This quiz covers its role in digestion, blood supply, and anatomical features, providing a comprehensive overview of this essential digestive organ.