What is the function of the gallbladder?

What the Gallbladder Does

The gallbladder stores and concentrates bile during fasting, then contracts after meals to deliver bile into the duodenum for fat digestion, while also modifying bile composition to prevent gallstone formation. 1

Primary Functions

Bile Storage and Concentration

• The gallbladder stores bile during the fasting state, with the sphincter of Oddi maintaining higher pressure in the common bile duct than in the duodenum or gallbladder to prevent premature bile release. 1
• Bile concentration occurs actively, not passively—as bile salts concentrate from 15-272 mmol/L, sodium, potassium, calcium, and lipid concentrations increase proportionally. 2
• The gallbladder can concentrate bile approximately 5-10 fold through active water and electrolyte absorption. 2

Coordinated Bile Delivery

• The gallbladder empties mainly after meals through coordinated contraction of the gallbladder and simultaneous relaxation of the sphincter of Oddi. 1
• Cholecystokinin (CCK) is the principal hormone controlling postprandial gallbladder emptying—this 33 amino acid polypeptide is released from the proximal small bowel in response to fat and protein ingestion. 3
• CCK binds to gallbladder receptors causing contraction while binding to inhibitory neurons at the sphincter of Oddi causing relaxation, leading to increased bile flow into the intestine. 3
• Gallbladder contraction occurs 5-20 minutes after food enters the stomach, well before gastric chyme reaches the duodenum (1-3 hours later), suggesting the digestive role may be less significant than traditionally thought. 4

Protective Functions Through Bile Modification

Prevention of Gallstone Formation

• The gallbladder actively modifies bile through concentration AND acidification to enhance solubility of cholesterol and calcium salts. 2
• As bile concentrates, the cholesterol saturation index decreases from 3.7 in dilute bile to 1.0-1.5 in concentrated bile, suggesting the gallbladder absorbs cholesterol and enhances its solubility. 2
• Progressive acidification accompanies concentration—bile pH decreases as bile salt concentration increases, with carbonate levels decreasing curvilinearly. 2
• Despite increasing calcium concentrations during concentration, calcium carbonate saturation index decreases from 3.62 in dilute bile to 0.12 in concentrated/acidified bile, preventing calcium stone formation. 2

Protection from Toxic Bile Acids

• Bile accumulation in the gallbladder reduces formation of secondary bile acids (deoxycholic acid and lithocholic acid), diminishing their concentration in enterohepatic circulation. 4
• This protects the liver, stomach mucosa, gallbladder, and colon from toxic hydrophobic effects of secondary bile acids. 4
• The presence or absence of a gallbladder in mammals determines whether hydrophobic or hydrophilic bile acids are synthesized. 4

Regulatory Mechanisms

Hormonal and Neural Control

• Both fasting and postprandial gallbladder motility are controlled by hormonal and neural mechanisms working in concert. 1
• Beyond gallbladder contraction, CCK inhibits gastric emptying, suppresses appetite, and increases intestinal peristalsis (the latter causing abdominal cramping with rapid IV infusion). 1, 3
• More complete gallbladder emptying and faster intestinal transit increase enterohepatic cycling of bile acids and lower the molar percent cholesterol of bile. 5

Clinical Implications

Normal vs. Abnormal Function

• A contracted gallbladder is normal after meals but may indicate chronic cholecystitis when seen in fasting patients. 6
• Biliary pain occurs from increased gallbladder pressure caused by abnormal contraction patterns with structural or functional outflow obstruction. 1
• Motility disturbances include hypokinesia (impaired contractility/hypomotility) and dyskinesia (partial obstruction, either structural or functional). 1

Functional Assessment

• Gallbladder function can be assessed using cholecystokinin-cholescintigraphy (CCK-CS) to measure gallbladder ejection fraction. 3, 6
• An abnormal ejection fraction (<38%) with typical biliary pain may suggest functional gallbladder disorder. 6