In addition to its numerous metabolic activities, the liver secretes bile. Bile is transported to the gallbladder, where it is stored. When food reaches the duodenum, the gallbladder releases bile, which emulsifies fat in the duodenum.
The liver produces bile, which emulsifies fat. The liver is also involved in cholesterol metabolism, the urea cycle, protein production, clotting factor production, detoxification, phagocytosis via the Kupffer cells lining the sinusoids, and receiving blood from the portal vein and hepatic artery.
The liver is attached to the inferior surface of the right dome of the diaphragm via the coronary ligaments. The bare area of the liver is a region devoid of peritoneum between the coronary ligaments and, therefore, lies in direct contact with the diaphragm. The falciform ligament is a peritoneal structure that courses between the left and right lobes of the liver and the anterior abdominal wall. The ligamentum teres is within the falciform ligament and is the embryonic remnant of the ductus venosus of the umbilical cord. The four lobes of the liver are as follows (Figure 9-2A and C):
- Right lobe. Positioned to the right of the inferior vena cava and gallbladder.
- Left lobe. Positioned to the left ligamentum teres.
- Quadrate lobe. Positioned posterior to the portal triad.
- Caudate lobe. Positioned anterior to the portal triad.
A. Visceral (inferior) view of the liver. B. Portal triad. C. Anterior view of the foregut with the body and pylorus of the stomach removed; the lesser omentum is also removed.
Functionally, the quadrate and caudate lobes are part of the left lobe because they are supplied by the left hepatic artery, drained by the left branch of the portal vein, and deliver bile via the left bile duct.
The portal triad lies between the caudate and quadrate lobes and is the structural unit of the liver (Figure 9-2B and C). The portal triad consists of the portal vein, proper hepatic artery, and the common hepatic duct. The portal vein is deep to the hepatic artery and the common hepatic duct.
- Proper hepatic artery. Branches from the celiac trunk via the common hepatic artery. The hepatic artery supplies oxygenated blood to the liver. The cystic artery arises from the hepatic artery to supply the gallbladder.
- Portal vein. Formed through the union of the splenic and superior mesenteric veins, deep to the pancreas. The portal vein collects nutrient-rich venous blood from the small and large intestines, where it is transported to the hepatic sinusoids of the liver for filtration and detoxification. The hepatic sinusoids empty into the common central vein, which empties into the hepatic veins and ultimately drains into the inferior vena cava. The flow of blood from one capillary bed (intestinal capillaries) through a second capillary bed (liver sinusoids) before its return by systemic veins to the heart is defined as the hepatic portal system.
- Common hepatic duct. The union of the left and right hepatic ducts forms the common hepatic duct. The common hepatic duct transmits bile produced in the liver to the gallbladder for storage.
results when there is an obstruction to the regular flow of blood through the sinusoids of the liver. There are many possible causes, including cirrhosis of the hepatocytes (liver cells). Signs of portal hypertension include hemorrhoids and gastroesophageal bleeding, which result from the obstruction of the portal venous blood flow through the liver and the increased flow of blood through alternate routes to reach the inferior vena cava (e.g., rectal and esophageal veins). When these alternate paths receive more blood than normal, the veins dilate, distend, and become more prone to hemorrhage. For example, esophageal varices
are distended esophageal veins, resulting from portal hypertension, and may precipitate life-threatening bleeding in the esophagus if hot or cold fluids are ingested or violent coughing occurs.
The gallbladder lies on the visceral surface of the liver, to the right of the quadrate lobe, and stores and concentrates bile secreted by the liver (Figure 9-2A–C). Bile is released into the duodenum when the gallbladder is stimulated after eating a fatty meal. Bile enters the cystic duct, which joins the common hepatic duct, becoming the common bile duct. The common bile duct courses within the hepatoduodenal ligament of the lesser omentum, deep to the first part of the duodenum, where it joins the main pancreatic duct. Together, the common bile duct and the main pancreatic duct enter the second part of the duodenum at the hepatopancreatic ampulla (of Vater). The sphincter of Oddi surrounds the ampulla and controls the flow of bile and pancreatic digestive enzyme secretions into the duodenum.
may form in the gallbladder and obstruct the flow of bile, resulting in inflammation and enlargement of the gallbladder. These stones may be composed of bilirubin metabolites, cholesterol, or various calcium salts. They frequently obstruct the gallbladder, causing retention of bile and the risk of rupture into the peritoneal cavity, which ultimately results in peritonitis