The liver is the largest gland of the human body with a weight of about 1300gms in females to 1600gm in males.
It is highly vascular and reddish-brown in color, located inside the abdomen, on the right upper quadrant.
The 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 the 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 the epigastrium is where the liver is naked, directly touching the anterior abdominal wall.
Surfaces and Borders
The liver is a pyramidal organ in shape. Its anatomy 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.
The anatomical right lobe consists of 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 of only the rest 1/6th.
The groove of the inferior vena cava on the right, ligamentum venosum on the left, and the porta hepatis below mark the boundaries of the caudate lobe, which is small and looks like a tail. It is sometimes called the caudate process and is attached with an even smaller finger-like projection called the papillary process.
The 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 on the inferior surface of the liver. It is situated between the two lobes – the caudate lobe and the Quadrate lobe.
Through porta hepatis, the main communication of the 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 the liver is supplied through the hepatic artery, and the rest 80% of the total blood of the liver is supplied through the portal vein. Both of them enter 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 the interlobular vein, which joins to form the sublobular vein, then the interlobar vein, and 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.
Inside the capsule, the lobes of the liver can be broken into small functional units called ‘Lobules,’ which are visible to the naked eye.
These lobules are hexagonal in shape and have cube-shaped hepatocytes.
As seen in the image above, hepatocytes are arranged in radiating columns from the central vein. Between these columns, sinusoids (blood vessels) containing blood from the hepatic artery and portal vein are present. This helps the content of the blood to come in close contact with hepatocytes for further processing.
These hepatocytes are specialized liver cells involved in the metabolism and synthesis of various essential substances for the body.
In the linings of the sinusoids, there are kupffer cells, which are hepatic macrophages. These kupffer cells destroy the old blood cells and foreign particles by ingesting them.
Now, the liver’s unit is classified under two different Classification.
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 the 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 three central veins, a total portal triad, and rest hepatocytes.
Functions of the Liver: The liver is a versatile organ doing huge metabolic activities. Its functions are:
1. Metabolism: Metabolism of carbohydrates, fats, proteins, everything occurs in the liver.
Liver stores carbohydrates as glycogen after a meal and releases it into the blood as glucose.
It also breaks down amino acids and nucleic acids into urea and uric acid, respectively.
Fats are converted to different forms as needed by the body for energy or storage.
2. Synthesis: Synthesis of bile, prothrombin, different clotting factors, albumin, etc. occur in the liver.
3. Excretion: Excretion of different drugs, heavy metals, toxin, bile pigments, cholesterol, etc. occurs through the liver.
4. Protection: Protective functions of the liver are conjugation, phagocytosis, destruction, antibody formation, and excretion.
5. 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 the liver, etc. They are hard to be treated, but not impossible.
Keep drinking alcohol, but be aware, your liver may be at risk.