Liver Anatomy, Histology and Functions in Detail
The liver is the largest gland of a human body. It is located inside the abdomen, on the right upper quadrant. An adult healthy liver weighs about 1300gm in females to 1600gm in males. Being highly vascular, it is reddish-brown in color.
Liver is located in the upper quadrant of the right hypochondrium of the abdomen. Being the largest gland, it has quite large dimensions. It occupies the whole of the right hypochondrium, extending up to the left lateral line, occupying most of the parts of epigastrium and left hypochondrium.
The liver is protected at its most part by the ribs and costal cartilages. It is placed safely in what is called a hepatic cavity. Only the upper part of epigastrium is the place where the liver is naked, directly touching the anterior abdominal wall.
Surfaces and Borders: Liver is a pyramidal organ in shape. It has five surfaces and one prominent border.
The five surfaces are:
- Anterior surface
- Posterior or the largest surface
- Superior surface
- Inferior surface
- Right or the lateral surface.
Out of all these five surfaces, the only inferior surface is well marked by the sharp inferior border. Others are more or less continuous, being separated by rounded borders.
The borders of the liver are more or less rounded, except for the inferior border. This inferior border separates the anterior surface and the inferior surface.
Lobes of the Liver: Visually, the liver is divided into two lobes- the greater right lobe, and the smaller left lobe. These right and left lobes are separated anteriorly and superiorly by the Falciform ligament, inferiorly by the ligamentum teres, and posteriorly by the ligamentum venosum.
But anatomically and physiologically, the liver is divided into four lobes:
- Right lobe
- Left lobe
- Caudate lobe
- Quadrate lobe.
Anatomical right lobe consists a few less than about 5/6th of the liver. It is the largest lobe and houses both Caudate and Quadrate lobes. The much smaller left lobe consists only the rest 1/6th.
The groove of inferior vena cava on the right, ligamentum venosum on the left and the porta hepatis on below marks the boundaries of caudate lobe, which is small and looks like a tail. It is sometimes called the caudate process, and is attached with even smaller finger-like projection called papillary process.
Quadrate lobe, on the other hand is rectangular in shape, as the name suggests. It is bounded by the sharp inferior border, the porta hepatis, gall bladder fossa and the ligamentum teres. It is also a part of the right lobe of the liver.
Porta Hepatis and Hepatic Drainage:
A. Porta hepatis: Porta hepatis is a 5cm long transverse fissure, lying in the inferior surface of the liver. It is situated between the two lobes – caudate lobe and Quadrate lobe.
Through porta hepatis, the main communication of liver takes place with other vessels. Through this, the Hepatic Artery, Portal vein, and Hepatic plexus of nerves enter the liver. Whereas the right and left bile ducts as well as some lymphatics leave the liver.
B. Blood Drainage: 20% of the total blood of liver is supplied through the hepatic artery, and rest 80% of the total blood of liver is supplied through the portal vein. Both of them enters through porta hepatis.
After entering into the liver, immediately both of these vessels divide into right and left branches. Within the liver, they divide into several segmental branches which divide into interlobar and then interlobular branches. These run into the portal canals. Their further ramifications lead them into hepatic sinusoids. There is a mixture of the blood of the Hepatic Artery and the portal vein inside the sinusoids. There are no anastomoses, so hepatic end branches are always ending arteries.
C. Venous Drainage: The blood from the hepatic sinusoids drain into the central vein. It then joins to form interlobular vein, which joins to form sublobular vein, then interlobar vein, and finally the hepatic vein. It then leaves the liver via porta hepatis and finally joins the inferior Vena cava.
D. Lymphatic drainage: The main lymph nodes associated with the liver are the caval nodes, hepatic nodes, the paracardial nodes and the coeliac nodes. These are the superficial lymph nodes.
The deep lymphatics drain into the inferior Vena cava nodes and the hepatic nodes.
Now, the liver’s unit is classified under two different Classifications.
A. The anatomical classification shows each hepatic lobule is composed of a central vein at the center and a hexagonal sidewall, with portal triads on each corner of the hexagon. The portal triad consists of a small branch of hepatic artery, portal vein and bile duct.
From each corner runs a series of hepatic cells or hepatocytes which joins with the side of the central vein.
B. The physiological classification shows that each hepatic lobule is formed consisting of 1/6th of the central vein from each of three central veins, a total portal triad and rest hepatocytes.
Functions of Liver: Liver is a versatile organ doing huge metabolic activities of the human body. Its functions are:
- Metabolism: Metabolism of carbohydrates, fats, proteins, everything occurs in the liver.
- Synthesis: Synthesis of bile, prothrombin, different clotting factors, albumin, etc. occur in the liver.
- Excretion: Excretion of different drugs, heavy metals, toxin, bile pigments, cholesterol etc. occur through the liver.
- Protection: Protective functions of the liver are conjugation, phagocytosis, destruction, antibody formation and excretion.
- Storage: Storage of glycogen, ferritin, fats, vitamin A, vitamin D etc occur in the liver.
Diseases of the liver include liver cirrhosis, hepatic carcinoma in situ, clear cell carcinoma of the liver, fatty liver, metastatic carcinoma of liver etc. They are hard to be treated, but not impossible.
Keep drinking alcohol, but be aware, your liver may be at risk.