Specialized liver cells called hepatocytes constitute about 70-80% of the liver mass. The liver comprises billions of hepatocytes that are connected by the biliary system, which is a system of bile ducts and blood vessels.
Reddish-brown in color, liver is the largest glandular organ of the human body. This wedge-shaped organ is located in the right upper quadrant of the abdomen. While a major part of the liver is placed in the right hypochondriac region and epigastric region of the abdomen, small parts of the liver are located in the left hypochondriac and right lumbar region.
Liver is enclosed by a layer of connective tissue called Glisson's capsule. It performs various vital bodily functions ranging from production of bile and metabolism of carbohydrates, fat, and proteins to detoxification. It is also the main hematopoietic organ in a fetus, which means that liver is responsible for the production of red blood cells in a fetus.
The liver continues to develop during early childhood years. It is believed that the liver becomes fully developed by the time one completes 15 years of age. It must be noted that the liver is the only organ that has the ability to regenerate itself from the existing healthy cells.
Anatomy and the Location of the Liver
The liver is located just below the diaphragm, and is connected to the diaphragm by five ligaments called falciform ligament, coronary ligament, right and left triangular ligaments, and the round ligament (which is derived from the embryonic umbilical vein).
It extends from the fifth right intercostal space to the right costal margin (the margin of the lowest rib on the right side). Right below the liver is a small, pear-shaped muscular sac called gallbladder. This tiny sac acts as a reservoir for bile, which is the digestive juice produced by the liver.
Bile is drained from the liver cells by several small ducts that form the hepatic duct. The hepatic duct joins the cystic duct from the gallbladder to form the common bile duct, which drains into the duodenum (the first part of the small intestine). Bile plays a vital role in the metabolism of fats.
Lobes of the Liver
It is the falciform ligament that attaches the liver to the anterior abdominal wall and marks the external anatomical division of the liver into the dominant right lobe and the smaller left lobe. When the liver is viewed from the front, only the left and the right lobe can be seen.
However, based on the features of the surface or when viewed from the posterior, the liver is divided into four anatomical lobes. These include right lobe (the largest lobe that accounts for about 65% of the total volume of the liver), quadrate lobe, caudate lobe, and the left lobe.
However, for the purposes of the surgical resection of the liver, this anatomical demarcation is not used. For surgical purposes, the functional division of the liver is used.
In 1898, James Cantlie referred to the specific regions of the liver, demarcating them on basis of left and right portal structures. Later, C. Couinaud divided the liver into eight segments, with each of these segments being functionally independent with their own blood supply (branch of the portal vein and hepatic artery) and biliary drainage (bile duct).
Under the functional system, Cantlie's line (an imaginary line or plane containing middle hepatic vein that runs from the inferior vena cava at the back to the middle of the gallbladder fossa at the front) divides the liver into the right and left lobe.
The right hepatic vein divides the right lobe into the anterior segment and posterior segment, and each of these segments is further divided into inferior and superior segments. The left hepatic vein divides the left lobe into the medial segment and lateral segment, and each of these segments is further divided into inferior and superior segments.
The caudate lobe lies on the inferior surface of liver between the inferior vena cava on the right, the ligamentum venosum (remnant of the fetal ductus venosus) on the left, and the porta hepatis in the front. The quadrate lobe lies between the fissure for the ligamentum teres (the remnant of the left umbilical vein of the fetus) and the gallbladder fossa.
Unlike the classical description where the quadrate lobe belongs to the right lobe, the quadrate lobe is considered to be a part of left lobe under Couinaud's classification.
Lobules of the Liver and Blood Supply
The lobes of the liver are made up of hexagonal-shaped microscopic units called lobules. The lobules, which comprise millions of hepatocytes, are arrangements of liver cells and sinusoids, with bile passageways through which bile empties into ducts. Each lobule comprises cellular plates that radiate from a central vein.
The central vein receives blood from the hepatic portal vein and hepatic artery through the sinusoids (vascular channels located between the rows of hepatocytes that receive blood from the portal triads) and empties into the right and left hepatic veins, which in turn drain into the vena cava.
The sinusoids receive oxygenated blood from the hepatic artery and nutrients from the small intestine via the portal vein. The 'portal triad' refers to the branches of the hepatic artery, hepatic portal vein, and bile duct that are located at the corners of the lobules.
The liver receives about 1.5 quarts of blood every minute through the hepatic artery (an artery which supplies 20% of the liver's blood) and portal vein (drains venous blood into the liver and supplies 80% of the liver's blood).
While right and left hepatic arteries carry oxygenated blood to the liver, the portal vein carries deoxygenated blood from the digestive tract to liver. This blood drains into the superior and inferior mesenteric veins, which along with the splenic vein form the portal vein. The portal vein splits into right and left branches, which supply blood to liver.
The blood carried by the portal vein contains the nutrients or other substances absorbed from the digestive tract, which are processed in the liver before these are either stored in the liver for future use or released into the hepatic veins joining the inferior vena cava.
Importance of the Liver
The liver helps in the synthesis of various substances that are vital for the healthy functioning of the human body. Some of its functions include:
- Synthesis of glucose from glycerol
- Metabolism of lipids and certain proteins
- Synthesis of certain proteins that help in the coagulation of blood
- Storage of vitamin A, iron, and copper
- Production of bile, which is a digestive juice that helps in the digestion of fats
- Neutralization and the removal of the toxins
Though the liver cells have an ability to regenerate or repair themselves, the liver function can get adversely affected due to certain medical conditions. Excessive consumption of fatty foods and alcohol can overburden the liver, thereby making one susceptible to liver diseases. Excessive alcohol damages the liver and affects its ability of metabolisation.
At times, prolonged use of drugs can also affect the functioning of the liver. Autoimmune disorders, hepatitis (inflammation of the liver), fatty liver disease, formation of liver cysts, liver cirrhosis, and liver cancer are some of the serious liver diseases that can affect the liver function.
Loss of appetite, nausea, vomiting, diarrhea, fatigue, and weakness are some of the early symptoms of liver failure in humans. Liver diseases are often diagnosed in the later stages, as the early symptoms are not very specific and might even occur due to other medical conditions.
Severe symptoms such as yellowing of skin, abdominal pain, swelling of the abdomen, dark urine, pale stools, itching, bruising, or bleeding appear only in the advanced stages.
At times, the liver function might deteriorate rapidly. It must be noted that acute liver failure is a medical emergency. Generally, dialysis or liver transplantation is recommended for the treatment of acute liver failure.
A healthy liver is extremely essential for the normal functioning of the body. Therefore, medical assistance must be immediately sought by anyone who has been experiencing the aforementioned symptoms.
The best way to keep the liver in a good condition would be to follow a healthy diet and refrain from excessive consumption of alcohol. Alcoholics come in the high-risk group for liver failure, which is why they must reduce alcohol intake and make the right lifestyle choices.
Disclaimer: The information provided here is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.