Hepatobiliary System Study Notes
The Liver
Largest single organ weighing between 1200–1600 g
Located in the right upper quadrant (RUQ) under the right hemi-diaphragm
Divided into right (1) and left lobes (2); larger right lobe can be subdivided into caudate and quadrate lobes
Falciform ligament separates left and right lobes and attaches the liver to the anterior abdominal wall
Porta hepatis on the inferior surface where the hepatic artery, portal vein, hepatic nerve plexus, lymphatics, and hepatic ducts enter/exit the liver
Portal triad: the hepatic artery, hepatic portal vein, and hepatic ducts (or bile ducts); named for their triangular arrangement
Covered by Glisson capsule (fibroelastic capsule)
Key functions: digestion, metabolism, immunity, storage of nutrients; liver is an accessory organ of digestion
Liver lobules (made up of hepatocytes) secrete electrolytes, lipids, bile acids, lecithin, and cholesterol
Bile contains salts necessary for fat digestion and absorption
Additional functions:- Vascular and hematologic: blood storage, clotting, bacteria removal
Metabolism of nutrients: fats, proteins, and carbohydrates
Metabolic detoxification & mineral and vitamin storage
Couinaud’s segmental anatomy
The Couinaud classification divides the liver into eight functionally independent segments
Each segment has its own vascular inflow, outflow, and biliary drainage
In the centre of each segment there is a branch of the portal vein, hepatic artery, and bile duct
In the periphery of each segment there is vascular outflow through the hepatic vein
Segments are numbered clockwise; Segment I (the caudate lobe) is located posteriorly and is not visible on a frontal view
Segment mappings:- Segment I — Caudate Lobe
Segment II — Lateral left lobe (superior)
Segment III — Lateral left lobe (inferior)
Segment IVa — Medial left lobe (superior)
Segment IVb — Medial left lobe (inferior)
Segment V — Anterior right lobe (inferior)
Segment VI — Posterior right lobe (inferior)
Segment VII — Posterior right lobe (superior)
Segment VIII — Anterior right lobe (superior)
Source: Nucleus Medical Media (2011). Segments of the Liver – Posterior view
Liver vascular anatomy
Receives blood from both arterial and venous sources
Hepatic artery: 25% of blood; branches from the celiac axis of the aorta
Hepatic portal vein: 75%; drains blood from the GI tract and spleen to the liver
Portal vein formation: confluence of the superior mesenteric vein (SMV) and splenic vein
Portal vein divisions:- Left portal vein supplies segments II, III, IV
Right portal vein divides into anterior portal veins supplying segments V and VIII, and posterior portal veins supplying segments VI and VII
Supplies liver with metabolic substances and allows processing of ingested substances
Hepatic veins: drain deoxygenated blood and blood filtered by the liver to the inferior vena cava (IVC); three hepatic veins drain the parenchyma: Right hepatic vein, Middle hepatic vein, Left hepatic vein
Portal venous system
(Intrahepatic and extrahepatic components connect to the liver via the portal system.)
Portal vein carries nutrient-rich blood from the GI tract to the liver for processing
Intrahepatic ducts and vascular channels interface with the portal system to support hepatic processing
Hepatic venous system
Drains deoxygenated and processed blood from the liver to the IVC via the hepatic veins
Three major hepatic veins: Right, Middle, and Left
The biliary tract
Formed by channels that collect bile from hepatic parenchyma and transport it to the duodenum
Divided into intrahepatic and extrahepatic bile ducts
Intrahepatic ducts:
1) Bile canaliculi unite to form segmental bile ducts with the following drainage pattern:
2) Segments VI and VII: right posterior duct (RPD), coursing more horizontally
3) Segments V and VIII: right anterior duct (RAD), coursing more vertically
4) Right posterior and anterior ducts unite to form the right hepatic duct (RHD)
5) Segmental bile ducts from II–IV unite to form the left hepatic duct (LHD)
6) The left and right hepatic ducts unite to form the common hepatic duct (CHD). Bile ducts from segment I drain into the angle of their union
Extrahepatic ducts:- The common hepatic duct is joined by the cystic duct from the gallbladder to form the common bile duct (CBD)
The CBD travels posteriorly to the duodenum and pancreas to unite with the main pancreatic duct to form the ampulla of Vater
The ampulla of Vater drains at the major duodenal papilla on the medial wall of the duodenum
The gall bladder
A sac-like organ lying on the inferior surface of the liver
Wall composed of mucosa, muscularis, and serosa or adventitia
Primary function: store and concentrate bile between meals
During interdigestive period bile flows from the liver via right or left hepatic ducts, meets resistance at the Sphincter of Oddi, and then flows to the gallbladder via the cystic duct
The mucosa absorbs water and electrolytes, concentrating bile salts, pigments, and cholesterol
After eating, the gallbladder contracts and the Sphincter of Oddi relaxes, forcing bile into the duodenum through the major duodenal papilla
The spleen
Largest of the secondary lymphoid organs located in the left upper quadrant (LUQ)
Concave, encapsulated, weighing approximately 150 g
Divided by a ridge into two regions: anterior (gastric) and posterior (renal)
Connective tissue strands extend through the spleen, creating compartments containing splenic pulp
White pulp: produces and grows immune cells as well as blood cells
Red pulp: purifies blood, removes dead or old blood cells
Roles:- Immune surveillance of blood-borne pathogens
Blood reservoir
Mononuclear phagocytes filter and cleanse the blood; lymphocytes mount immune responses to blood-borne microorganisms
Blood supply: arterial blood from the splenic artery (branch of the celiac artery)
Venous drainage: splenic vein, which drains into the portal vein
The Pancreas
The pancreas is both an endocrine and an exocrine gland
Endocrine portion produces hormones; exocrine portion produces digestive enzymes
Location and orientation:- Retroperitoneal organ located in the epigastric region behind the stomach, between the spleen and the duodenum
Lies transversely, slightly obliquely, on the posterior abdominal wall
Parts:- Head tucked in the concavity and surrounded by the duodenum
Body lies behind the base of the stomach
Tail abuts the spleen
Neck lies between the body and head, anterior to the superior mesenteric artery (SMA) and vein (SMV)
Uncinate process emerges from the lower part of the head, behind the SMA; an extension of the angle formed at the junction of the lower and left lateral borders of the head
Anatomy mapping (visual cue):- 1 Duodenum
2 Head of pancreas
3 Body of pancreas
4 Tail of pancreas
5 Neck of pancreas
6 Uncinate process
Blood supply to the pancreas
Derived from a rich blood supply from both the celiac axis and the superior mesenteric artery
Celiac axis trifurcates into:- Common hepatic artery (CHA)
Splenic artery
Left gastric artery (LGA)
CHA runs toward the right on the superior border of the proximal body of the pancreas
Splenic artery runs toward the distal body and tail of the pancreas
Splenic artery supplies the neck, body, and tail via pancreatic branches; the largest is the greater pancreatic artery
Inferior pancreatic artery arises from the superior mesenteric artery (SMA) to supply the body and tail
The arterial supply forms an important collateral circulation between the celiac axis and the SMA
Venous drainage:- Body and neck drain into the splenic vein
Head drains into the superior mesenteric vein and portal vein
Exocrine pancreas
Pancreatic juice consists of two secretory products essential for digestion:- Digestive enzymes
Bicarbonate
Enzyme production and secretion:- Enzymes synthesized and secreted by exocrine acinar cells
Bicarbonate secreted by epithelial cells lining small pancreatic ducts
Pancreatic enzymes:- Proteases — protein digestion
Pancreatic lipase — triglycerides to monoglycerides and free fatty acids
Amylase — starch breakdown
Structure:- Pancreas composed of acini networks of ducts that secrete enzymes and alkaline fluids
Acinar cells organized into spherical lobules around small secretary ducts
Secretions drain into ducts leading to the pancreatic duct (Wirsung duct)
Pancreatic duct empties into the common bile duct at the ampulla of Vater
Some individuals have an accessory duct (duct of Santorini) that drains into the duodenum at the minor duodenal papilla
Endocrine pancreas
The endocrine pancreas comprises cells within the pancreas that synthesize and secrete hormones
The endocrine portion forms islets of Langerhans
Major cell types within the islets and their products:- Alpha cells (A cells) secrete glucagon
Beta cells (B cells) produce insulin and are the most abundant islet cells
Delta cells (D cells) secrete somatostatin (also produced by other endocrine cells in the body)
The endocrine cells lie adjacent to blood capillaries to secrete hormones into the bloodstream
Recommended texts
Weir, J., & Abrahams, P. H. (2003). Imaging Atlas of Human Anatomy. Mosby
Fleckenstein, P. & Tranum-Jensen, J. (2001). Anatomy of Diagnostic Imaging, 2nd ed. Munksgaard
McCance, K.L., & Huether, S.E. (2006). Pathophysiology. The Biologic Basis for Disease in Adults and Children, 5th ed. Elsevier Mosby
Connections and relevance
Couinaud segmentation is fundamental for surgical planning and radiologic interpretation
Portal triad anatomy underpins liver imaging, transplant planning, and assessment of biliary obstruction
The dual blood supply to the pancreas (celiac axis and SMA) explains how pancreatic lesions may affect vascular supply and how collateral circulation can develop
The biliary tract anatomy (intra- and extrahepatic) is essential for understanding gallbladder pathology, bile duct obstructions, and procedures like ERCP
The liver’s broad range of functions links to systemic health: metabolism, detoxification, immunity, and nutrient storage
Practical implications include diagnosis and management of jaundice, portal hypertension, biliary colic, pancreatitis, and hepatic disease