Lobules of liver
Image Caption : Visualization of liver lobules, with a central vein running through the middle of each, intersperesed with portal triads (a branch of the hepatic artery, hepatic vein, and a bile duct). Hexagonal-shaped liver lobules are composed of plates of hepaocytes radiating out from a central vein; at each of the six corners of the lobule is a portal triad composed of a hepatic artery and portal vein as well as a bile duct. Blood from the hepatic artery and portal vein travels through the lobules in capillaries called sinusoids, is processed by the hepatocytes, and empties into the central vein. Flowing in the opposite direction, bile produced in the hepatocytes flows through bile canaliculi that run towards the bile ducts in the portal triads; these bile ducts eventually empty into the common hepatic ducts that direct bile toward the duodenum. Besides processing incoming nutrients and producing bile, hepatocytes also store vitamins and detoxify the blood.
The liver is the largest gland in the body, weighing about three pounds in an adult. It is also one of the most important organs. In addition to being an accessory digestive organ, it plays a number of roles in metabolism and regulation. The liver lies inferior to the diaphragm in the right upper quadrant of the abdominal cavity and receives protection from the surrounding ribs.
The liver is divided into two primary lobes: a large right lobe and a much smaller left lobe. In the right lobe, some anatomists also identify an inferior quadrate lobe and a posterior caudate lobe, which are defined by internal features. The liver is connected to the abdominal wall and diaphragm by five peritoneal folds referred to as ligaments. These are the falciform ligament, the coronary ligament, two lateral ligaments, and the ligamentum teres hepatis. The falciform ligament and ligamentum teres hepatis are actually remnants of the umbilical vein, and separate the right and left lobes anteriorly. The lesser omentum tethers the liver to the lesser curvature of the stomach.
The porta hepatis ("gate to the liver") is where the hepatic artery and hepatic portal vein enter the liver. These two vessels, along with the common hepatic duct, run behind the lateral border of the lesser omentum on the way to their destinations. As shown inFigure, the hepatic artery delivers oxygenated blood from the heart to the liver. The hepatic portal vein delivers partially deoxygenated blood containing nutrients absorbed from the small intestine and actually supplies more oxygen to the liver than do the much smaller hepatic arteries. In addition to nutrients, drugs and toxins are also absorbed. After processing the bloodborne nutrients and toxins, the liver releases nutrients needed by other cells back into the blood, which drains into the central vein and then through the hepatic vein to the inferior vena cava. With this hepatic portal circulation, all blood from the alimentary canal passes through the liver. This largely explains why the liver is the most common site for the metastasis of cancers that originate in the alimentary canal.
The liver receives oxygenated blood from the hepatic artery and nutrient-rich deoxygenated blood from the hepatic portal vein.
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The liver is located primarily in the right hypochondriac and epigastric regions of the abdomen, just beneath the diaphragm. It is the largest gland in the body. On the surface, the liver is divided into two major lobes and two smaller lobes. The functional units of the liver are lobules with sinusoids that carry blood from the periphery to the central vein of the lobule.
The liver receives blood from two sources. Freshly oxygenated blood is brought to the liver by the common hepatic artery, a branch of the celiac trunk from the abdominal aorta. Blood that is rich in nutrients from the digestive tract is carried to the liver by the hepatic portal vein.
The liver has a wide variety of functions and many of these are vital to life. Hepatocytes perform most of the functions attributed to the liver, but the phagocytic Kupffer cells that line the sinusoids are responsible for cleansing the blood.
Liver functions include the following:
- synthesis of bile salts
- synthesis of plasma protein
- carbohyrate metabolism
- lipid metabolism
- protein metabolism
National Cancer Institute / National Institutes of Health
A hepatic lobule is a small division of the liver defined at the histological scale. It should not be confused with the anatomic lobes of the liver (caudate lobe, quadrate lobe, left lobe, and right lobe), or any of the functional lobe classification systems.
The two-dimensional microarchitecture of the liver can be viewed from multiple different perspectives:
The term "hepatic lobule", without qualification, typically refers to the classical lobule.
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