Hepatobiliary System, Pancreas, and Spleen: Comprehensive Study Notes
General Characteristics and Functions of the Liver
Definition: The liver is the largest gland in the human body.
Fetal Function: During fetal life, the liver serves as a hematopoietic organ (site of blood cell production).
Metabolic and Secretory Functions:
Storage: Stores glycogen for energy regulation.
Excretion: Secretes bile, which aids in the emulsification of fats.
Location:
Situated in the right upper quadrant (RUQ) of the abdomen.
It is protected by the thoracic (rib) cage and the diaphragm.
Mobility: The liver moves with the descent of the diaphragm during respiration. This mobility facilitates the process of palpation during clinical examinations.
Glisson’s Capsule: The connective tissue capsule that encloses the liver.
Anatomical and Functional Divisions of the Liver
Anatomical Lobes:
The liver is divided into two major anatomical lobes (large right lobe and small left lobe) by the attachment of the falciform ligament.
The right lobe is further subdivided into two accessory lobes: the quadrate lobe and the caudate lobe. These are defined by the gallbladder, the fissure for the ligamentum teres, the inferior vena cava (IVC), and the fissure for the ligamentum venosum.
Functional (Physiologic) Division:
Divided into functional right and left lobes by the Cantlie line (a line between the gallbladder fossa and the Inferior Vena Cava).
Each functional lobe receives its own primary branch of the hepatic artery and hepatic portal vein and is drained by its own hepatic duct.
Surgical Segments (Couinaud’s Segmental Anatomy):
The liver is subdivided into four divisions and then into eight surgically resectable hepatic segments.
Each segment is served independently by a secondary or tertiary branch of the portal triad.
This allows for the surgical resection of individual segments without damaging remaining tissue.
The right, intermediate (middle), and left hepatic veins course within three planes or fissures-right portal (R), main portal (M), and umbilical (U)-which serve as guides to the divisions.
Three divisions are further subdivided at the transverse portal plane (T).
The left medial division and caudate lobe are considered specific hepatic segments.
The Porta Hepatis and Visceral Impressions
Porta Hepatis (Hilum of the Liver):
A transverse fissure on the posteroinferior surface of the liver, located between the caudate and quadrate lobes.
Entry/Exit point for: Hepatic portal vein, hepatic artery proper, lymphatic vessels, hepatic nerve plexus, and hepatic ducts.
Visceral Impressions: The postero-inferior surface of the liver makes contact with several organs, leaving impressions:
Esophageal area
Gastric area
Pyloric area
Duodenal area
Renal area
Suprarenal area
Colic areas
Peritoneal Ligaments and Fetal Remnants
Falciform Ligament: Extends between the superior anterior abdominal wall and the liver.
Ligamentum Teres (Round Ligament):
The fibrous remnant of the left umbilical vein.
Found on the free margin of the falciform ligament.
It joins the left branch of the portal vein in the porta hepatis.
Coronary Ligament: Anchors the posterior border of the liver to the diaphragm on both sides.
Triangular Ligaments (Right and Left): Form the extremities of the coronary ligament on both sides.
Ligamentum Venosum: The remnant of the fetal ductus venosus, which shunted blood from the umbilical vein to the IVC to bypass the liver. It is attached to the portal vein and ascends to join the IVC.
Bare Area: A portion of the posterior surface of the liver that is not covered by peritoneum, allowing the liver to be in direct contact with the diaphragm.
Blood Circulation, Drainage, and Innervation of the Liver
Dual Blood Supply:
Hepatic Portal Vein (): Carries nutrient-rich venous blood from the alimentary tract (except lipids, which bypass via lymphatics) to the liver sinusoids.
Hepatic Artery (): Supplies oxygenated arterial blood.
Venous Drainage:
Blood is conducted to the central vein of each lobule via liver sinusoids.
Central veins drain into hepatic veins (Right, Middle, Left), which open directly into the Inferior Vena Cava (IVC).
Right hepatic vein: Divides the right lobe into anterior and posterior segments.
Middle hepatic vein: Divides the liver into functional right and left lobes.
Left hepatic vein: Divides the left lobe into medial and lateral parts.
Innervation: The Hepatic Plexus is the largest derivative of the celiac plexus. It contains sympathetic fibers from the celiac plexus and parasympathetic fibers from the anterior and posterior vagal trunks.
Lymphatic Drainage:
Superficial and deep lymphatics drain to the porta hepatis and eventually the thoracic duct.
Posterior areas drain through the diaphragm to posterior mediastinal nodes and the right lymphatic duct.
Posterior left lobe drains to the esophageal hiatus then to left gastric nodes.
Falciform ligament drains to parasternal nodes.
Round ligament drains to the umbilicus and anterior abdominal wall.
Efferent vessels from hepatic nodes drain into celiac lymph nodes.
Anatomical Supports of the Liver
Primary Supports:
Attachment of the hepatic veins to the IVC.
Coronary and triangular ligaments.
Secondary Supports:
Right kidney.
Right colonic angle.
Duodenopancreatic complex.
Tertiary Support:
Falciform ligament attachment.
Surgical Significance: These supports are so robust that the liver can only be slightly rotated even if the peritoneal ligaments are severed.
Clinical Correlates of the Liver
Liver Trauma:
The liver is soft and friable. Mechanisms of injury include fractures of lower ribs, penetrating injuries (stab/gunshot), or blunt trauma (automobile accidents).
Injury causes severe hemorrhage. Segmental distribution of vessels allows surgeons to ligate specific areas to remove tumors (metastasis).
Liver Biopsy:
Types: Open (Laparotomy), Laparoscopic, Percutaneous (US/CT guided, requiring the patient to hold breath in full expiration), and Transvenous.
Transvenous methods include Transjugular (Internal jugular to hepatic vein) and Transfemoral.
Liver Abscess:
A pus-filled mass, more common in the right lobe due to its size and blood supply.
Causes: Injury, intraabdominal infection through portal circulation, or biliary tract infection.
Organisms: Entamoeba histolytica, E. coli, Klebsiella, Streptococcus, Staphylococcus, and anaerobes.
Treatment involves drainage and antibiotics.
The Biliary Apparatus
Bile Pathway: Hepatocytes $\rightarrow$ bile canaliculi $\rightarrow$ interlobular biliary ducts $\rightarrow$ intrahepatic portal triad ducts $\rightarrow$ Hepatic Ducts (Left and Right).
Common Hepatic Duct: Formed by the union of the right and left hepatic ducts.
Common Bile Duct (CBD):
Formed by the union of the cystic duct and common hepatic duct.
Length: .
Course: Lies in the right free margin of the lesser omentum (anterior to portal vein, right of hepatic artery) $\rightarrow$ behind the first part of the duodenum $\rightarrow$ groove on the posterior surface of the head of the pancreas $\rightarrow$ joins main pancreatic duct.
Ampulla of Vater: The dilation formed by the union of the CBD and main pancreatic duct.
Major Duodenal Papilla: The opening in the second part of the duodenum where the ampulla enters.
Sphincter of Oddi: Muscles surrounding the ends of the ducts.
Blood Supply to CBD:
Proximal: Cystic artery.
Middle: Right hepatic artery.
Retroduodenal: Posterior superior pancreaticoduodenal and gastroduodenal arteries.
The Gallbladder and Cystic Duct
Description: A pear-shaped sac on the undersurface of the liver with a capacity of .
Parts: Fundus (projects below liver margin), Body (on visceral surface), Neck (continuous with cystic duct).
Hartmann’s Pouch: A diverticulum at the neck where gallstones frequently lodge.
Cystic Duct:
Length: .
Spiral Valve of Heister: Mukosal folds that keep the duct open and resist sudden dumping of bile.
Function: Continuously stores and concentrates bile. Fat entering the duodenum triggers the release of cholecystokinin, causing the gallbladder to contract and deliver bile.
Blood Supply: Cystic artery (usually from the right hepatic artery).
Innervation: Celiac plexus (sympathetic ; visceral afferent pain) and Vagus nerve (parasympathetic).
Triangle of Calot (Cystohepatic Triangle):
Boundaries: Cystic duct, Common hepatic duct, and Visceral surface of the liver.
Contents: Cystic artery and lymph node. Crucial for surgeons during cholecystectomy.
Clinical Correlates of the Biliary System
Biliary Atresia: Failure of bile ducts to canalize. Signs: Jaundice after birth, clay-colored stools, dark urine. Treated with the Kasai procedure (Hepatoportoenterostomy) or liver transplant.
Congenital Choledochal Cyst: Weakness in the bile duct wall; can contain of bile. Causes obstructive jaundice and increases malignancy risk.
Gallstones (Cholelithiasis):
Composed chiefly of cholesterol crystals.
Choledocholithiasis: Stones in the bile duct.
Primary: Formed in the duct. Secondary: Formed in gallbladder then migrated.
Biliary Colic: Spasms caused by the gallbladder attempting to expel a stone.
Obstructive Jaundice: Blocked bile drainage causing tea-colored urine and acholic (clay-colored) stools.
Cholecystitis: Inflammation of the gallbladder. Murphy’s Sign: Pain on inspiration when the gallbladder touches the examiner's hand.
Cholecystoenteric Fistula: Gallbladder ulcerates into adjacent viscera (usually superior duodenum or transverse colon). A large stone may cause bowel obstruction at the ileocecal valve (gallstone ileus).
The Pancreas
Classification: Both exocrine (pancreatic juice from acinar cells) and endocrine (glucagon and insulin from islets of Langerhans).
Location: Secondarily retroperitoneal (except the tail) at the level of vertebrae.
Parts:
Head: Within the concavity of the duodenum. Includes the uncinate process (posterior to SMA/SMV).
Neck: In front of the portal vein and superior mesenteric vessels. The splenic vein joins the SMV behind the neck to form the hepatic portal vein.
Body: To the left of superior mesenteric vessels, posterior to the omental bursa.
Tail: Mobile segment passing between layers of the splenorenal ligament toward the splenic hilum, anterior to the left kidney.
Ducts:
Main Pancreatic Duct (Wirsung): Runs from tail to head.
Accessory Pancreatic Duct (Santorini): Opens at the minor duodenal papilla.
Blood Supply:
Head: Pancreaticoduodenal arteries (Superior from gastroduodenal; Inferior from Superior Mesenteric).
Body/Tail: Splenic artery branches.
Pancreatic Clinical Correlates
Pancreatitis: Inflammation due to tissue damage, infection, or common channel reflux.
Pancreatic Cancer: occur in the head, often compressing the bile duct causing jaundice. Cancer in the neck/body can obstruct the portal vein or IVC. Detected late with early metastasis to the liver via the portal vein. Treated via the Whipple procedure (Pancreaticoduodenectomy).
Cystic Fibrosis: Inherited mutation in the CFTR gene causing dysfunctional chloride transport. Results in thick, viscid mucus that obstructs pancreatic ducts, leading to fibrosis.
The Spleen
Characteristics: Largest lymphatic organ. Situated beneath the left diaphragm near ribs .
Borders: Anterior and superior borders are sharp and notched; posterior and inferior borders are rounded.
Ligaments:
Gastrosplenic: Connects to the greater curvature of the stomach; contains short gastric and left gastroepiploic vessels.
Splenicorenal: Connects to the left kidney; contains splenic vessels and the pancreatic tail.
Vascularity:
Splenic Artery: Largest branch of the celiac trunk. It is an "end artery" (lack of intra-splenic anastomosis).
Trauma: Most frequently injured abdominal organ. Blunt trauma can rupture the thin capsule, leading to profuse intraperitoneal hemorrhage and shock.
Diagnostic Imaging: ERCP vs. MRCP
ERCP (Endoscopic Retrograde Cholangiopancreatography):
Invasive: Uses endoscope and X-ray.
Nature: Both diagnostic and therapeutic (stone removal, stenting).
Potential Complications: Bleeding, pancreatitis, infection.
MRCP (Magnetic Resonance Cholangiopancreatography):
Non-invasive: Uses MRI (magnets and radio waves).
Nature: Strictly diagnostic.
Contraindications: Metal implants (pacemakers, aneurysm clips).
Active Learning Activity
Question: What specific part of the gastrointestinal tract (GIT) is the endoscope cannulated during ERCP?
Answer: The second (descending) portion of the duodenum, specifically toward the major duodenal papilla.
Laboratory Instructions
Dissection Tasks (June 25, 2026):
Open the stomach along the anterior surface with scissors.
Identify gastric folds (rugae).
Extend the cut into the pylorus to identify the pyloric sphincter.
Extend the cut into the anterior wall of the duodenum.
Spread the second part of the duodenum to identify circular folds (plicae circulares) and the major duodenal papilla on the posterior-medial wall.