Gallbladder and bile

The gallbladder is an intraperitoneal organ derived from the endoderm that is located inferior to the liver. It is divided into a fundus, a body, often an infundibulum, and a neck. The gallbladder is perfused by the cystic artery, a branch of the right hepatic artery that drains into the cystic vein and the hepatic sinusoids. It receives sympathetic innervation via the celiac plexus, parasympathetic innervation via the vagus nerve, and sensory innervation via the branches of the phrenic nerve. The main function of the gallbladder is bile storage. Bile is secreted by the liver and facilitates digestion, neutralization of gastric acid, fat absorption, and excretion of bilirubin and cholesterol. The biliary tract, which is divided into intrahepatic and extrahepatic bile ducts, transports bile to the intestine. The ductules are intrahepatic bile ducts that unite to form the left and right hepatic ducts, which drain bile from the liver. The extrahepatic bile ducts include the cystic duct and the common hepatic duct, which unite to form the common bile duct. The common bile duct unites with the pancreatic duct and drains into the hepatopancreatic ampulla in the duodenum. Excessive saturation of bile with cholesterol or bilirubin leads to gallstone formation. Diseases of the biliary tract include cholecystitis, primary sclerosing cholangitis, and biliary atresias among many others.

The gallbladder is a hollow, pear-like-shaped (piriform) organ that lies on the cystic plate (gallbladder bed) under the liver segments IVB and V. The cystic plate is a fibroareolar tissue that attaches the superior surface of the gallbladder to the liver.

Anatomy

• Location: intraperitoneal organ
• Size and volume
  • Length: 7–10 cm
  • Width: 2.5 cm (at its widest point)
  • Volume
    • 30–35 mL under normal conditions
    • Can hold up to 300 mL if the cystic duct is obstructed
• Composition/structure
  • Fundus
  • Body
  • Infundibulum: the section that narrows from the body to the neck
    • Sometimes described in literature as part of the neck
    • Inaccurately described in some literature as synonymous with the Hartmann Pouch
  • Neck: connects to the cystic duct → common hepatic duct → common bile duct
  • Possible Hartmann gallbladder pouch
    • A dilation that may be seen on the ventral aspect of the gallbladder, proximal to the gallbladder neck
    • Most common site of gallstone impaction
    • Previously thought to be a pathologic finding but now thought to be an anatomic variant

Function

• Storage of bile
  • Bile drains from the liver via small bile ducts.
  • Cholecystokinin (CCK) stimulates the gallbladder to contract, which then releases bile through the cystic duct, into the second part of the duodenum.
• Concentration of bile: by absorption of electrolytes and water

Vasculature

• Arterial blood supply: cystic artery (branch of the right hepatic artery)
• Venous drainage
  • Neck: cystic veins → portal vein
  • Body and fundus: hepatic sinusoids

Innervation

• Sympathetic: via the celiac plexus
• Parasympathetic: hepatic branch of the vagus nerve
• Sensory: fibers from the phrenic nerve → referred pain to the right shoulder area (via C3 nerve fibers)

Cholecystitis causes referred pain to the right shoulder region because the phrenic nerve originates from spinal nerves C3–C5, which also provide somatic sensation to the shoulder area.

Layers of the gallbladder wall ^[1]

• Serosa (on the inferior peritoneal surface) and adventitia (on the superior hepatic surface)
• Muscularis externa
• Lamina propria
• Mucosa
  • Simple columnar epithelium with microvilli
  • Secretes mucin

Anatomy

The biliary tree is divided into the intrahepatic and extrahepatic bile ducts.

Intrahepatic bile ducts

• Bile canaliculi → intrahepatic bile ductules (canals of Hering) → segmental bile ducts → sectional ducts
  • Right posterior duct (RPD): drains segment VI and VII
  • Right anterior duct (RAD): drains segment V and VIII
    • Right posterior and anterior ducts connect and form the right hepatic duct (RHD).
    • Bile ducts from segments II–IV connect and form the left hepatic duct (LHD).
• Common hepatic duct (CHD): formed by the right and left hepatic ducts

Extrahepatic bile ducts

• Common bile duct
  • Formed by the common hepatic duct and cystic duct
  • Travels in the free edge of the lesser omentum, in the hepatoduodenal ligament
  • Posterior to the duodenum and the pancreas
  • Connects with the main pancreatic duct
  • Drains into the hepatopancreatic ampulla (ampulla of Vater)
• Hepatobiliary triangle
  • An anatomical space formed by the common hepatic duct, the cystic duct, and the inferior border of the liver
  • Contains the cystic artery and the cystic lymph node (Lund's node)
  • During cholecystectomy, the hepatobiliary triangle must be carefully identified to prevent damage to the cystic artery and extrahepatic biliary system.
• Calot triangle: an anatomical space formed by the common hepatic duct, the cystic duct, and the cystic artery

The portal triad consists of the hepatic artery, portal vein, and common bile duct.

Composition

Bile is a secretion produced by the liver and stored in the gallbladder that aids in digestion, neutralization of gastric acid, fat absorption, and excretion of bilirubin and cholesterol.

• Bile pigments
  • Bilirubin (yellow pigment)
    • Excreted as water-soluble (conjugated) bilirubin
    • Conjugated within the liver
    • Transported in the blood bound to carrier proteins
    • Lipid soluble (unconjugated) metabolite of hemoglobin
  • Biliverdin (green pigment): a byproduct of hemoglobin breakdown
• Bile acids
  • Primary bile acids
    • Cholic acid, chenodeoxycholic acid
    • Synthesized in the liver from cholesterol (rate-limiting enzyme: cholesterol 7-α hydroxylase)
    • Stored in the gallbladder
  • Secondary bile acids
    • Deoxycholic acid, lithocholic acid
    • Synthesized in the intestinal lumen by the action of bacterial flora
  • Bile acids are conjugated with glycine or taurine to form bile salts and become water-soluble.
• Other components: phospholipids, cholesterol, water, and ions

A deficiency of bile acids can result in fat malabsorption and cholesterol stones in the gallbladder.

Function

• Emulsion and absorption of fats (including fat-soluble vitamins)
• Excretion of bilirubin and cholesterol (the process by which the majority of cholesterol is removed from the body)
• Antimicrobial effect (may disrupt bacterial membranes)
• Transport of IgA

Enterohepatic circulation

Substances metabolized in the liver are excreted into the bile.

• Bile salts (∼ 95% of bile acids are reabsorbed back into the liver to be recycled)
  • Pass into the intestinal lumen where bacteria break down primary bile acids into secondary bile acids
  • Get reabsorbed in the intestinal mucosa (primarily the proximal and distal ileum)
  • Return to the liver via portal circulation
• Bilirubin
  • ∼ 80% is excreted in feces as stercobilin .
  • ∼ 20% enters enterohepatic circulation.
    • ∼ 90% is recycled in the liver.
    • ∼ 10% is excreted by the kidney.

Gallstones

There are different types of gallstones (see “Cholelithiasis” and “Cholecystitis” for more information):

• Cholesterol stones (∼ 80% of cases)
  • Radiolucent with radiopaque areas due to calcifications (< 20%)
  • Composed of cholesterol and calcium carbonate
• Pigment gallstones
  • Black pigment gallstones
    • Radiopaque
    • Associated with hemolytic diseases such as sickle cell anemia, hereditary spherocytosis
    • Composed of calcium bilirubinate
  • Brown pigment gallstones
    • Radiolucent
    • Associated with infection

References:^[1][2]

• Derived from endoderm
• Starts to develop during the 4th week of embryonic development
• Formed from the hepatic diverticulum (hepatic bud)
  • The bile duct arises from the hepatic diverticulum, which narrows and connects with the midgut.
  • The gallbladder and cystic duct form from a ventral outgrowth of the bile duct.
• See “Embryology of the gastrointestinal tract” for more information.

Disorders of the biliary tract

• Primary sclerosing cholangitis
• Primary biliary cholangitis
• Ascending cholangitis
• Choledocholithiasis
• Cholecystitis
• Porcelain gallbladder
• Biliary colic
• Cholelithiasis
• Gallbladder polyp
• Cholangiocarcinoma
• Mirizzi syndrome
• Biliary atresia
• Choledochal cyst
• Caroli disease
• Cholesterolosis (cholesterol deposits within macrophages, which causes a yellowish, speckled mucosal coloration due to excess cholesterol in bile)

Disorders of the bile

• Neonatal jaundice
• Crohn disease
• Primary bile acid diarrhea
• Small intestine bacterial overgrowth
• Intrahepatic cholestasis of pregnancy
• Celiac disease
• Chronic pancreatitis
• Gilbert syndrome
• Crigler-Najjar syndrome
• Dubin-Johnson syndrome
• Rotor syndrome
• Primary bile acid malabsorption (PBAM)

Disorders of the intestine

• Short bowel syndrome
• Crohn disease