Liver and gallbladder
The liver and gallbladder are the two accessory organs of the gastrointestinal tract, which carry out a multifunctional role that aids digestion and homeostasis. The liver consists of several lobes and receives its blood supply mainly from the hepatic portal vein. This organ also detoxifies the body, so take good care of it because it is your best friend while celebrating after your exams!
The gallbladder is found inferiorly to the liver, being involved in the storage and release of bile into the duodenum.
Liver: hypochondriac and epigastric regions
Gallbladder: right upper quadrant
Liver: diaphragmatic surface, visceral surface, right lobe, left lobe, caudate lobe, quadrate lobe, segments
Gallbladder: fundus, body, beck, extrahepatic biliary tract
Liver: hepatic artery, hepatic portal vein, hepatic veins
Gallbladder: cystic artery, right hepatic artery, posterior superior pancreaticoduodenal artery, gastroduodenal arteries, cystic veins
Sympathetic: celiac and superior mesenteric plexuses
Parasympathetic: vagus nerve
This article will describe the anatomy and function of the liver and gallbladder.
- Blood vessels
The liver is an intraperitoneal organ found inferior to the diaphragm and deep to the 7th to 11th ribs. The location of the liver is such that you just can’t miss it, as it spans through three abdominal regions; right hypochondriac, epigastric and left hypochondriac.
Several peritoneal ligaments support the position of the liver: round ligament of liver (ligamentum teres), falciform ligament, coronary ligament, triangular ligaments and lesser omentum. The lesser omentum comprises the hepatogastric and hepatoduodenal ligaments which connect the liver to the lesser curvature of the stomach and duodenum. It is quite important as it carries the portal triad: bile duct, hepatic artery and hepatic portal vein.
Reflections of the peritoneum form three recesses:
- The subphrenic recess which separates the diaphragmatic surface of the liver from the diaphragm.
- The subhepatic space which is situated directly inferior to the liver. It projects between the inferior surface of the liver and the right kidney as the hepatorenal recess (Morison pouch).
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The liver has two surfaces; diaphragmatic and visceral. The surfaces show several fissures, which together with the ligaments divide the liver into four lobes:
- Left and right lobes, separated by the falciform ligament
- Caudate and quadrate lobes, delimited by the fissures of the visceral surface
The liver can also be divided functionally into eight segments according to the portal blood supply and biliary drainage.
The microscopic anatomy of the liver parenchyma is represented by the hepatic lobules. They consist of cords of hepatocytes surrounding a central vein. Sinusoids and portal triads are also part of the hepatic lobules.
The diaphragmatic surface is covered by visceral layer of peritoneum, except posteriorly at the ‘bare area’. The bare area is in direct contact with the diaphragm. This area contains a groove for the inferior vena cava as it travels through the abdomen towards the thorax and heart.
The visceral surface of the liver is also covered with peritoneum, except at the gallbladder fossa and porta hepatis. This surface contains three fissures which are oriented in the shape of the letter ‘H’:
- Left and right sagittal fissures
- Transverse fissure (porta hepatis)
The visceral surface of the liver shows impressions of the neighbouring organs. These indentations are the: gastric, esophageal, suprarenal, renal, colic, duodenal areas, and gallbladder fossa.
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The liver has metabolic, exocrine and endocrine roles. It synthesizes plasma proteins which maintain osmotic pressure, transport micronutrients and act in blood clotting. Vitamins A, D, and K, iron and glycogen are important metabolic nutrients stored in the liver. They are released into the bloodstream when needed. The liver also modifies the action of various endocrine hormones and synthesizes bile, which is stored in the gallbladder.
The gallbladder is a small hollow intraperitoneal organ. It is located on the visceral surface of the liver, between the right and quadrate liver lobes. The superior part of the duodenum, hepatic flexure and proximal transverse colon, are posteriorly related to it.
There are three anatomical parts of the gallbladder. From lateral to medial these are:
- Fundus which points inferoanteriorly. It projects onto the anterior abdominal wall at the intersection of the right 9th rib and the lateral margin of the rectus abdominis muscle.
- Body which lies in the gallbladder fossa of the liver.
- Neck (infundibulum) with spiral mucosal folds.
Bile travels between the liver, gallbladder and duodenum via the biliary tree. Hepatocytes synthesize and secrete bile via the right and left hepatic ducts. These ducts fuse into a single common hepatic duct in the lateral part of the porta hepatis.
The neck of the gallbladder funnels off into the short cystic duct. This duct combines with the common hepatic duct to form the common bile duct. The cystic duct, common hepatic duct and part of the inferior border of the liver form the triangle of Calot.
The common bile duct unites with the pancreatic duct to form the ampulla of Vater (hepatopancreatic ampulla), which opens into the duodenum on the major duodenal papilla. The flow of bile and pancreatic juice is controlled by the sphincter of Oddi.
The main gallbladder function is to store and concentrate bile, which then gets distributed to the duodenum through the biliary tract. While ingesting a meal, the presence of fats and proteins in the intestines stimulates the release of cholecystokinin. This peptide hormone causes simultaneous contraction of the body and relaxation of the neck of the gallbladder. Once the pressure within the biliary tree increases, the sphincter of Oddi relaxes. Bile then flows from the biliary tree directly into the duodenum.
One aspect making the liver a distinct and interesting organ is its dual blood supply. The hepatic portal vein is responsible for 75 to 80% of the blood reaching the liver, bringing nutrients from the gastrointestinal tract for processing and metabolism. It is formed by the union of the splenic and superior mesenteric veins. The portal vein reaches the liver as part of the portal triad, traversing the hepatoduodenal ligament.
The rest of the liver’s blood supply requirements are fulfilled by the hepatic artery, which stems from the common hepatic artery, a branch of the celiac trunk. Upon reaching the liver, the hepatic artery divides into left and right branches, each one supplying the segments of the left and right lobes of the liver respectively.
The hepatic veins (right, middle, left) are responsible for the venous drainage of the liver. They flow into the inferior vena cava. Do you want to find out more blood supply details, including the ‘danger zones’ during transplant surgery? Click below for more anatomy!
The gallbladder and cystic duct are supplied by the cystic artery, a branch of the right hepatic artery. The bile duct is supplied by four major blood vessels; cystic, right hepatic, posterior superior pancreaticoduodenal, and gastroduodenal arteries. These supply the proximal, middle and retroduodenal parts of the duct, respectively.
Venous drainage of the gallbladder and cystic duct is via cystic veins, which flow into the hepatic vein. The bile duct is drained by the superior pancreaticoduodenal vein, which in turn empties into the hepatic portal system.
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The liver parenchyma receives autonomic innervation from the hepatic plexus. The parasympathetic input is provided by branches of the vagus nerves (CN X). The sympathetic fibers originate from the celiac plexus. The liver capsule is innervated by the branches of the lower intercostal nerves.
The hepatic plexus is also responsible for providing autonomic innervation to the gallbladder and the extrahepatic biliary system. The parasympathetic division stemming from the vagus nerves causes the gallbladder to contract and bile to flow within the duodenum. The sympathetic component arising from the celiac plexus inhibits contractions of the gallbladder, it also conveys pain sensation.
Jaundice is defined as a yellowish discoloration of the sclera, skin, and mucous membranes due to an excessive amount of bilirubin (hyperbilirubinemia). Bilirubin is the end-product resulting from the breakdown of erythrocytes. It is metabolized in the liver and released in the gallbladder as part of bile. Therefore, excessive erythrocyte hemolysis, liver pathologies and biliary tree obstruction can result in jaundice. Specific examples include Gilbert syndrome, hepatitis, cirrhosis and carcinomas.
Jaundice becomes clinically evident only when serum bilirubin levels exceed 2 mg/dl. Apart from yellowing, physical findings can include right upper quadrant pain, fever, anorexia, malaise, acholic stools and dark coloured urine.