Makindo Medical Notes

Anatomy of the Gallbladder and Biliary System

The gallbladder and biliary system are integral parts of the digestive system, primarily involved in the storage and transport of bile. The bile ducts, gallbladder, and associated structures form the biliary system, which is crucial for the digestion of fats. The gallbladder itself is a pear-shaped organ located beneath the liver.

Gallbladder Anatomy

• Location: The gallbladder is located on the inferior surface of the liver, in the right upper quadrant of the abdomen. It lies in a shallow depression called the gallbladder fossa.
• Structure: The gallbladder is a small, hollow organ about 7-10 cm long and can hold up to 50 mL of bile.
  • Fundus: The rounded, distal end that projects anteriorly.
  • Body: The main part of the gallbladder, which stores bile.
  • Neck: The narrow part that connects the body of the gallbladder to the cystic duct.

Biliary Anatomy

• Hepatic Ducts: The right and left hepatic ducts drain bile from the liver and merge to form the common hepatic duct.
• Cystic Duct: The cystic duct connects the neck of the gallbladder to the common hepatic duct. Bile flows in and out of the gallbladder via the cystic duct.
• Common Bile Duct: The common hepatic duct merges with the cystic duct to form the common bile duct, which transports bile to the duodenum.
• Sphincter of Oddi: A muscular valve at the end of the common bile duct that controls the flow of bile and pancreatic juice into the duodenum. It prevents reflux of duodenal contents into the biliary system.
• Ampulla of Vater: The area where the common bile duct and pancreatic duct meet before emptying into the duodenum.

Physiology of the Gallbladder and Biliary System

The primary function of the gallbladder and biliary system is to store, concentrate, and transport bile, which is essential for the digestion and absorption of fats.

Functions of the Gallbladder and Biliary System

• Bile Storage: The gallbladder stores bile produced by the liver. Between meals, bile accumulates and is stored in the gallbladder.
• Bile Concentration: The gallbladder concentrates bile by absorbing water and electrolytes, increasing the potency of bile salts for fat digestion.
• Bile Secretion: During digestion, particularly in response to a fatty meal, the hormone cholecystokinin (CCK) is released, stimulating the gallbladder to contract and release bile into the duodenum via the common bile duct.

Composition of Bile

• Bile Salts: Derived from cholesterol, bile salts are crucial for the emulsification of fats, allowing lipase enzymes to break them down for absorption.
• Bilirubin: A waste product from the breakdown of hemoglobin, bilirubin is excreted in bile and gives bile its characteristic yellow-green colour.
• Cholesterol: Excreted in bile, cholesterol helps in fat digestion and is also a precursor for bile salt formation.
• Water and Electrolytes: Aid in the transport of bile and absorption processes.

Bile Production and Flow

• Bile Production: Bile is continuously produced by the liver and is transported through the bile ducts. It is either stored in the gallbladder or flows directly into the duodenum.
• Bile Flow to the Duodenum: After a meal, particularly one high in fats, CCK stimulates the gallbladder to contract, releasing concentrated bile through the cystic duct and into the common bile duct. From there, bile flows into the duodenum to aid in the digestion of fats.

Regulation of Bile Secretion

• Cholecystokinin (CCK): This hormone is released by the small intestine in response to the presence of fats. CCK triggers the contraction of the gallbladder and relaxation of the sphincter of Oddi, allowing bile to flow into the duodenum.
• Secretin: Stimulates the liver to produce bile and enhances the flow of bile into the duodenum, particularly when the duodenum is acidic.
• Vagus Nerve: The parasympathetic nervous system, through vagal stimulation, can promote gallbladder contraction during the cephalic phase of digestion.

Blood Supply

• Arterial Supply: The gallbladder receives its blood supply from the cystic artery, which typically arises from the right hepatic artery.
• Venous Drainage: The cystic veins drain into the portal venous system, where blood is filtered through the liver.

Nerve Supply

• Sympathetic Innervation: The sympathetic nerves reduce bile secretion and inhibit gallbladder contraction.
• Parasympathetic Innervation: The vagus nerve stimulates gallbladder contraction, promoting bile release during digestion.

Clinical Relevance

• Cholelithiasis (Gallstones): Gallstones are formed when substances in bile, such as cholesterol or bilirubin, become concentrated and crystallize. They can obstruct the bile ducts, causing pain, infection, or inflammation (cholecystitis).
• Cholecystitis: Inflammation of the gallbladder, often due to obstruction by gallstones. It causes right upper quadrant pain, fever, and tenderness (Murphy’s sign).
• Biliary Colic: Pain caused by the temporary obstruction of the cystic duct by gallstones, typically occurring after meals.
• Choledocholithiasis: Gallstones within the common bile duct, which can cause jaundice, cholangitis, or pancreatitis.
• Cholangitis: Infection of the bile ducts, which can occur when bile flow is obstructed. It is a medical emergency and is typically treated with antibiotics and biliary drainage.
• Gallbladder Cancer: A rare but serious form of cancer that often presents late and is associated with gallstones and chronic inflammation.