The gallbladder is a gastrointestinal organ located within the abdominal cavity. It is used as a temporary storage for bile, a fluid produced in the liver. It is concentrated and released from the gallbladder in response to eating.
It is a peritoneal structure, and lays high in the abdomen, in the right hypochondriac region. Anatomically it is a small sac reminiscent of a pear in shape, laying in a fossa between the right and quadrate lobes on the inferior aspect of the liver.
The gallbladder is a pear-shaped sac, with a storage capacity of 30-50ml. It is typically divided into three parts:
- Fundus: The rounded, end portion of the gallbladder; which projects into the inferior surface of the liver.
- Body: The largest part of the gallbladder. It is occasionally in contact with the transverse colon and proximal duodenum.
- Neck: Here, the gallbladder tapers to become continuous with the cystic duct, leading to the biliary tree. The neck contains a mucosal fold, known as Hartmann’s Pouch. This is a common location for gallstones to become lodged, causing cholestasis.
The Biliary Tree
Bile is secreted from the gallbladder into the gastrointestinal tract via a series of ducts, known as the biliary tree. These ducts extend from the liver, communicating with the gallbladder and pancreas, and end at an opening into the duodenum.
The biliary tree begins with the left and right hepatic ducts, which drains bile from the liver where it has been synthesised. These two ducts amalgamate to form the common hepatic duct, which runs alongside the hepatic vein. As the common hepatic duct descends, it is joined by the cystic duct, which is a continuation of the neck of the gallbladder. The common hepatic duct and cystic duct combine to form the common bile duct.
As the common bile duct continues to descend, it passes posteriorly to the proximal duodenum and joins with the pancreatic duct of the pancreas, forming the hepatopancreatic ampulla of Vater. This then empties into the duodenum. The opening into the duodenum is known as the major duodenal papilla – it is regulated by a muscular valve, the sphincter of Oddi.
The Gallbladder is entirely surrounded by peritoneum, binding it to the visceral covering of the liver. It lies in close proximity to the following structures:
- Anteriorly and superiorly: Inferior border of the liver and the anterior abdominal wall.
- Posteriorly: Transverse colon and the proximal duodenum.
- Inferiorly: Biliary tree and duodenum.
Arterial supply to the gallbladder is via the cystic artery. This artery is derived from the hepatic artery proper, a branch of the common hepatic artery which arises from the coeliac trunk. The gallbladder receives venous drainage from the cystic vein, which drains directly into the portal vein.
In addition to the cystic artery and vein, the gallbladder communicates with the liver through several very small veins and arteries.
The gallbladder receives parasympathetic, sympathetic and sensory innervation. The coeliac plexus carries sympathetic and sensory fibres, while the vagus nerve delivers parasympathetic innervation. Parasympathetic stimulation produces contraction of the gallbladder, and the secretion of bile into the cystic duct. However, the main stimulator of bile secretion is cholecystokinin, which is secreted by the duodenum and travels in the blood.
Lymph from the gallbladder drains into the cystic node, situated at the gallbladder neck. The cystic node then empties into the hepatic lymph node, and ultimately to the coeliac node.
Clinical Relevance: Gallstones
Gallstones are small lumps of solid material that form in the gallbladder. They are relatively common and often asymptomatic, however they can be associated with pain, jaundice and inflammation of the gallbladder
There are several types of gallstones, including cholesterol and pigment stones (cholesterol stones are the most common). They are formed when there are high concentrations of cholesterol in the gallbladder.
Untreated gall stones can travel and inflame the pancreas.
The risk of gallstones increases with age, pregnancy and obesity. They are more common in females than males. Once diagnosed, most symptomatic patients have surgical removal of the gallbladder (cholecystectomy); which is now often performed via laparoscopic (key-hole) surgery. Patients are also often prescribed painkillers and antibiotics to reduce pain and limit infection whilst awaiting surgery.