Home › Histology › Gallbladder and Biliary Tract

Gallbladder and Biliary Tract

Vesica biliaris

For medical students2 min readUpdated 2026-10-10

The gallbladder and extrahepatic biliary tract form a system responsible for the storage, concentration, and release of bile into the gastrointestinal tract. A distinct histological feature of these organs' walls is the complete absence of a submucosa.

Gallbladder Volume40–70 mL

Wall Thickness1.5–2.0 mm

Duct LengthThe common bile duct reaches about 7 cm

Key FeatureAbsence of submucosa (*tela submucosa*)

Formation of the Biliary Duct System

Anatomically, bile drainage from the liver begins with the right and left hepatic ducts. In the region of the porta hepatis, they merge to form the common hepatic duct (ductus hepaticus communis).

This duct then unites with the cystic duct (ductus cysticus) originating from the gallbladder to form the common bile duct (ductus choledochus), which empties directly into the duodenum.

Bile flow is regulated by the digestive cycle:

Between meals, the sphincter at the opening of the common duct is closed, and bile flows retrogradely via the cystic duct into the reservoir — the gallbladder.
During digestion, the sphincter relaxes and the gallbladder contracts, expelling bile into the intestine.

Histological Structure of the Wall

The wall of the extrahepatic biliary tracts and the gallbladder has a layered structure similar to the intestinal tube, but consists of only three tunics. The submucosa is absent.

1. Mucosa (tunica mucosa)

Forms numerous folds, with a specialized spiral fold located within the cystic duct that helps regulate bile flow.

The epithelium is simple columnar absorptive with microvilli. Microvilli on the apical surface facilitate water absorption, leading to bile concentration.
The lamina propria consists of loose connective tissue rich in elastic fibers. Mucous tubuloalveolar glands can be found here in the neck region of the gallbladder, while the duct epithelium contains goblet cells that secrete mucus.

2. Muscular Layer (tunica muscularis)

Relatively thin, composed of smooth muscle bundles interspersed with connective tissue layers. In the gallbladder, myocytes are oriented circularly, whereas in the ducts they have a spiral orientation. Circular thickenings of the muscle layer form sphincters:

At the neck of the gallbladder and the origin of the cystic duct.
At the terminal portion of the common bile duct.

3. Outer Layer

Represented primarily by the serosa (tunica serosa), based on fibrous connective tissue. The ducts typically lie within a peritoneal fold, whereas the gallbladder is covered by mesothelium only on its inferior surface.

Functions and Clinical Significance

The primary function of the gallbladder mucosa is concentration. Through active water absorption by the epithelium, especially during periods of bile stasis between meals, the concentration of biliary components increases significantly.

This mechanism is directly linked to an important clinical pathology: when water is excessively absorbed, poorly soluble substances precipitate out of solution. Most commonly, cholesterol crystallizes, accounting for 80–90% of the mass of formed gallstones.

Embryogenesis

The liver and biliary tract share a common origin, developing from the endoderm of the midgut (the "hepatic field"). A hepatic diverticulum forms and divides into two parts:

The cranial portion gives rise to hepatocytes and cholangiocytes (the epithelium of the intrahepatic ducts).
The caudal portion forms the epithelium of the common bile duct and gallbladder.

The stroma and vasculature develop from mesenchyme, with the portal venous system originating from the vitelline veins.

Frequently asked questions

What are the deep mucosal invaginations of the gallbladder penetrating into the muscular layer called?

Deep epithelial invaginations extending into the muscular wall of the gallbladder are called Rokitansky-Aschoff sinuses.

Rokitansky-Aschoff sinuses — cystic epithelial invaginations penetrating deep into the organ's wall.

They are identified microscopically in chronic cholecystitis and are a hallmark of adenomyomatosis, which is characterized by wall thickening due to epithelial and smooth muscle hyperplasia. Small calculi may form within the lumen of these invaginations.

Which hormones and neurotransmitters stimulate contraction of the gallbladder smooth muscle?

The primary stimulants of gallbladder contraction and motility include:

Cholecystokinin (CCK) — induces contraction of the gallbladder and biliary ducts; the primary hormone driving bile expulsion.
Bombesin — stimulates gallbladder motility and bile release; produced by gastric P-cells and the brain.

Additional minor stimulants of bile evacuation include gastrin, secretin, and substance P.

Inhibitors of gallbladder contraction include glucagon, calcitonin, VIP, pancreatic polypeptide, and sympathetic nervous system activation.

How does the gallbladder wall differ from the intestinal wall?

The main histological difference is that the gallbladder wall completely lacks a submucosa (tela submucosa). Consequently, the mucosa transitions directly into the muscular layer.

What type of epithelium lines the gallbladder and why?

Simple columnar absorptive epithelium. The brush border (microvilli) is essential for active water absorption and bile concentration.

How is the common bile duct formed?

It is formed by the union of the common hepatic duct (carrying bile from the liver) and the cystic duct (leading from the gallbladder).

From which embryonic germ layer does the gallbladder epithelium derive?

The epithelium of the gallbladder and ducts develops from the foregut/midgut endoderm (the caudal part of the hepatic diverticulum).

Go deeper

Mechanisms of water absorption by absorptive cells
Histogenesis of the cholangiocytic lineage
Sphincteric apparatus of the terminal common bile duct (Sphincter of Oddi)
Pathogenesis of cholesterol gallstone formation at the cellular level