Gallbladder and Biliary Tract

The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Bile is secreted by hepatocytes into thin channels called canaliculi. These canaliculi lead into slightly larger interlobular bile ductules, which are part of the portal triads at the “corners” of hepatic lobules. The bile leaves the liver via the right and left hepatic ducts, which join together to form the common hepatic duct. The common hepatic duct joins with the cystic duct to form the common bile duct, which empties into the small intestine. If the sphincters leading into the intestines are closed, bile will travel via the cystic duct into the gallbladder for storage.

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Development

  • The gallbladder and biliary tree begin to develop in the 3rd–4th weeks of gestation.
  • Derived from endoderm
  • Hepatic diverticulum (sometimes called the liver bud): 
    • An outpouching from the ventral foregut of the primitive gut tube 
    • Cranial bud of the hepatic diverticulum (large) forms:
      • Liver
      • Intrahepatic ducts
      • Extrahepatic portions of the hepatic ducts
      • Common bile duct: connection between the hepatic diverticulum and the foregut (remnant of hepatic diverticulum)
    • Caudal bud of the hepatic diverticulum (small): 
      • Gallbladder 
      • Cystic duct: connection between the caudal bud and the hepatic diverticulum

Gross Anatomy of the Gallbladder

Location

  • In the RUQ of the abdomen
  • Immediately under the right lobe of the liver in the gallbladder fossa
  • Connected to the visceral surface of the liver via the cystic plate
  • Sits on top of the superior part of the duodenum
Anatomic relationships of the pancreas to surrounding organs

Anatomic relationships of the pancreas to surrounding organs:
Note that the liver and stomach are light gray and that the intestines have been removed completely in order to allow better visualization of this posterior organ.

Image by BioDigital, edited by Lecturio

Structure of the gallbladder

  • Shape: pear-shaped sac
  • Size:
    • 7–10 cm long
    • 4–5 cm wide
    • Volume: approximately 50 mL
  • Fundus:
    • Rounded base of the organ
    • Usually projects slightly beyond the inferior margin of the liver
  • Body: 
    • Main portion of the organ
    • In direct contact with:
      • Visceral surface of the liver
      • Superior part of the duodenum
  • Neck: 
    • Typically makes an S-shaped bend
    • Empties into the cystic duct 
    • Spiral valves (of Heister): 
      • Undulating folds or valves in the cystic duct
      • Keep the duct open so bile can easily be diverted into the gallbladder when distal sphincters are closed
      • Helps prevent dumping of bile into the intestines during sudden increases in intraabdominal pressure (e.g., coughing) when sphincters are closed
Gallbladder

Location and basic anatomy of the gallbladder and major biliary ducts

Image: “The gallbladder stores and concentrates bile, and releases it into the two-way cystic duct when it is needed by the small intestine” by OpenStax College. License: CC BY 4.0

Gross Anatomy of the Biliary Tree

Bile, a digestive fluid produced and secreted by hepatocytes in the liver, is transported to the gallbladder and small intestines by a series of branching bile ducts known collectively as the biliary tree.

Intrahepatic bile ducts

Ducts that originate within the liver itself are known as intrahepatic bile ducts and can be divided into:

  • Bile canaliculi: 
    • Narrow channels located between sheets of hepatocytes within hepatic lobules (hexagon-shaped functional units in the liver)
    • Drain into bile ductules at the exterior of the hepatic lobule
  • Bile ductules (also called interlobular bile ducts): 
    • Part of the portal triads located at the “corners” of each hepatic lobule, which contain:
      • Hepatic arterioles
      • Portal venules
      • Bile ductules 
    • Ultimately drain into the right or left hepatic ducts
  • Hepatic ducts:
    • Intrahepatic and extrahepatic segments
    • Right hepatic duct: drains the right lobe of the liver 
    • Left hepatic duct: drains the left lobe of the liver
Microscopic_Anatomy_of_Liver

Microscopic anatomy of the liver:
Bile is produced in the hepatocytes and secreted into the bile canaliculi. These canaliculi drain into the bile ductules (located next to the portal arterioles and venules). The bile ductules ultimately drain into the right and left hepatic ducts.

Image: “The liver receives oxygenated blood from the hepatic artery and nutrient-rich deoxygenated blood from the hepatic portal vein” by OpenStax College. License: CC BY 4.0

Extrahepatic bile ducts

Extrahepatic bile ducts are located outside the liver and are continuous with the intrahepatic bile ducts. There are many normal anatomic variants. These ducts include:

  • Extrahepatic segments of the right and left hepatic ducts
  • Common hepatic duct: formed via the combination of the right and left hepatic ducts
  • Cystic duct: 
    • Outflow tract of the gallbladder
    • Approximately 7 mm in diameter
    • Contains valves of Heister
    • Many normal anatomic variants
  • Common bile duct: 
    • Formed via the combination of the common hepatic duct and the cystic duct
    • Size:
      • Approximately 6 mm in diameter
      • Approximately 6–8 cm in length
    • Runs posterior to the duodenum 
    • Runs through the head of the pancreas, where it joins with the main pancreatic duct to form a swelling called the hepatopancreatic ampulla (also known as the ampulla of Vater)
      • Located within the head of the pancreas, just prior to its insertion into the small intestine
      • Empties into the descending part of the duodenum via an opening called the major duodenal papilla
      • Contains the hepatopancreatic sphincter (also known as the sphincter of Oddi): controls release of bile and pancreatic juice

Microscopic Anatomy

There are 3 primary layers in the wall of the gallbladder (from internal to external):

  • Mucosa: 
    • Contains ridges/folds that flatten when gallbladder fills/distends 
    • Simple columnar epithelial cells:
      • Line the lumen of the gallbladder
      • Contain Na+-ATP pumps to help concentrate bile
      • Connected to one another via tight junctions
      • Intercellular space: clear spaces between epithelial cells where water is being absorbed (unable to move back into the lumen due to tight junctions)
    • Lamina propria: 
      • Collagenous connective tissue
      • Contains blood vessels 
  • Muscularis externa: 
    • Thin layer of smooth muscle
    • Directly underneath the lamina propria of the mucosa
  • Serosa:
    • Connective tissue layer
    • Merges with the Glisson capsule of the liver 
  • Differences between gallbladder wall and other intestinal lumens:
    • No muscularis mucosa (within the mucosal layer)
    • No submucosal layer
    • Muscularis externa is much thinner
  • Bile ducts have the same structure as the gallbladder (except bile canaliculi lumen, which are lined by the apical poles of hepatocytes, no epithelium)
Histologic slide depicting gallbladder and mucosal folds

1) Histologic slide depicting the 3 layers of the gallbladder, in addition to the lumen and neighboring hepatic tissue
2) Histologic slide depicting the mucosal folds and ridges, as well as the thin layer of smooth muscle found in the gallbladder

Image by Geoffrey Meyer, PhD.

Related videos

Neurovasculature

Blood and lymphatics

  • Arterial blood supply: 
    • Gallbladder: Cystic artery, which most commonly arises from the right hepatic artery 
    • Hepatic ducts: branches of the hepatic artery
    • Retroduodenal portion of the common bile duct: 
      • Posterior superior pancreaticoduodenal artery 
      • Gastroduodenal artery
  • Venous drainage: 
    • Body and fundus of gallbladder: small veins that empty into the hepatic sinusoids
    • Neck and cystic duct: cystic veins → portal vein 
    • Hepatic and common bile duct: posterior superior pancreaticoduodenal vein → portal vein
  • Lymphatic drainage: cystic lymph nodes → hepatic nodes→ celiac nodes
Liver irrigation

Overview of the abdominal arterial blood supply:
The celiac trunk is the 1st major branch of the abdominal aorta. The trunk supplies the liver, stomach, spleen, pancreas and parts of the esophagus and duodenum with oxygenated blood.
The celiac trunk gives off the left gastric artery, splenic artery, and the common hepatic artery. The common hepatic artery divides into the hepatic artery proper, the gastroduodenal artery, and the right gastric artery, all of which can be seen here.

Image by Lecturio.

Innervation

The gallbladder and biliary tree are primarily innervated by 3 nerves/complexes:

  • Celiac nerve plexus: 
    • Sympathetic fibers (trigger bile storage)
      • Relaxation of the gallbladder
      • Contraction of sphincter muscles
    • Visceral afferent fibers → pain sensation
  • Vagus nerve: parasympathetic fibers (trigger bile release)
    • Contraction of the gallbladder
    • Relaxation of sphincter muscles
  • Right phrenic nerve: sensory somatic afferent fibers

Functions of the Gallbladder and Bile

Functions of the gallbladder

  • Storage of bile:
    • 40–50 mL in normal conditions 
    • Up to 300 mL in cases of biliary obstruction
  • Concentration of bile: 
    • Mucosal Na+-ATP pumps divert Na+ from the bile into the lamina propria.
    • Water follows the Na+ into the lamina propria (is unable to move back into the gallbladder lumen because of the tight occluding junctions at the surface)
    • Results in concentration of bile within the lumen
  • Release of bile: muscular layer contracts to release bile into the intestinal lumen when needed

Bile

Bile is a dark green-yellowish brown fluid produced by the liver. 

  • Composition: 
    • 97% water
    • 0.7% bile salts: critical for emulsification of fats
    • 0.5% fats, including:
      • Cholesterol: for excretion
      • Phospholipids: critical for emulsification 
    • 0.2% bilirubin: 
      • Primary pigment responsible for the color of bile (and ultimately stool)
      • Waste product from the breakdown of old/damaged RBCs in the spleen
  • Functions: 
    • Emulsion and absorption of lipids 
    • Absorption of the fat-soluble substances, such as vitamins A, D, E, and K
    • Excretion of bilirubin and cholesterol
    • Bile salts stimulate bowel movement.
    • Helps neutralize the hydrochloric acid entering the intestine from the stomach (pH of bile: 7.6–8.6) 
    • Antiseptic action against microorganisms present in food
  • Basic physiology:
    • Cholecystokinin:
      • GI hormone that is released when fatty chyme enters the duodenum
      • Causes contraction of the gallbladder and relaxation of the sphincter of Oddi
    • Hepatocytes produce about 500–1000 mL of bile per day
    • Bile acids are reabsorbed in the ileum → portal vein → liver (enterohepatic circulation)

Clinical Relevance

  • Cholelithiasis: presence of stones in the gallbladder. The stones are predominantly of the cholesterol type, while the rest are composed of bilirubin (pigment stones) and other mixed components. Individuals are commonly asymptomatic but may present with biliary colic (intermittent pain in the RUQ, usually after a fatty meal); the pain is caused by gallbladder contractions around the stones. The diagnosis is established by ultrasonography. 
  • Porcelain gallbladder: chronic gallstones irritate the gallbladder wall, leading to extensive calcium deposition and brittle, hard walls. Porcelain gallbladder carries an increased risk of gallbladder adenocarcinoma. 
  • Cholecystitis: inflammation of the gallbladder usually resulting from obstruction of the cystic duct by a gallstone. Cholecystitis presents with RUQ abdominal pain, fever, and leukocytosis. The diagnosis is usually made clinically and confirmed via ultrasonography. Management is usually surgical (cholecystectomy).
  • Acute cholangitis: life-threatening condition that develops as a result of stasis and infection of the biliary tract. Acute cholangitis is characterized by fever, jaundice, and abdominal pain. Septic shock, liver abscess, and multiorgan dysfunction are potential serious complications. 
  • Primary sclerosing cholangitis: chronic inflammatory condition that is characterized by fibrosis and stricture of the biliary ductal system. Presentation is with an insidious onset of fatigue, pruritus, and jaundice, which can progress to cirrhosis and complications related to biliary obstruction. The exact etiology is unknown, but there is a strong association with inflammatory bowel disease. 
  • Primary biliary cirrhosis: chronic disease resulting in autoimmune destruction of the intrahepatic bile ducts. The typical presentation is that of a middle-aged woman presenting with pruritus, fatigue, and RUQ abdominal pain. Slow damage to the liver tissue can lead to scarring, fibrosis, and eventually cirrhosis.
  • Cholangiocarcinoma:  type of cancer that forms in the bile ducts. The risk factors include primary sclerosing cholangitis, hepatolithiasis, cystic fibrosis, cirrhosis, hepatitis B and C, and certain liver flukes. Cholangiocarcinoma presents with jaundice, pruritus, abdominal pain, clay-colored stools, and fatigue. 
  • Jaundice: abnormal yellowing of the skin and/or sclera caused by the accumulation of bilirubin. Bilirubin is excreted in the bile, so abnormal biliary excretion can lead to jaundice. Jaundice can be clinically appreciated when the serum bilirubin levels rise to > 2–3 mg/dL. 

References

  1. Hundt M, Wu CY, Young M. (2021). Anatomy, abdomen and pelvis, biliary ducts. StatPearls. Retrieved August 28, 2021, from  https://www.ncbi.nlm.nih.gov/books/NBK459246/
  2. Jones M, Hannoodee S. (2021). Anatomy, abdomen and pelvis, gallbladder. StatPearls. Retrieved August 28, 2021, from https://www.statpearls.com/ArticleLibrary/viewarticle/32113
  3. Drake RL, Vogl AW, Adam Mitchell WM. (2020). Gray’s Anatomy for students, 4th ed. Churchill Livingstone/Elsevier. 
  4. Moore KL, Dalley AF,& Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Lippincott Williams & Wilkins, a Wolters Kluwer business.

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