Article by Dr Raghuram Y.S. MD (Ay) & Dr Manasa, B.A.M.S
Liver has the privilege of being the –
– Second largest organ in the human body (skin is the first largest organ)
– Heaviest internal organ
– The largest gland in the human body
– Major metabolic organ and an important accessory digestive organ
Location
It majorly occupies the right upper abdomen and middle abdomen and also extends a bit into the left upper abdomen. It lies under the diaphragm, a muscular partition between the organs of chest and abdominal cavity. It has two lobes of unequal shape and size. It is located to the right of the stomach and overlies the gallbladder.
Shape of the liver
Shape of the liver can be compared to that of a prism or wedge.
The base of the wedge of the liver is towards the right while its apex is towards the left (pointing towards the left of abdomen).
Colour and consistency of the liver
Liver is dark reddish brown / pinkish brown in colour. It is soft in consistency. It is highly vascular and is easily friable.
Weight of the liver
Liver approximately weighs 1500 grams (1.5 kilograms / 3.3 pounds approximately). While this is the average weight, it may vary between individuals, 970-1,860 grams in men and 600-1,770 grams in women (Wikipedia).
Width of the liver
Human liver is roughly 6 inches / 15 centimetres in width.
Blood Vessels and interior of the liver
The main blood vessels related to the liver are the hepatic artery and the portal vein.
– Hepatic artery – takes its origin from the aorta and carries blood via the celiac trunk.
– Portal Vein – carries nutrient rich blood from gastrointestinal tract, spleen and pancreas.
These blood vessels further subdivided into small capillaries. These capillaries are known as liver sinusoids which lead into hepatic lobules.
Hepatic lobules – Hepatic lobules are the functional units of the liver. Millions of hepatocytes i.e. hepatic cells make up each lobule of the liver. They are the basic metabolic cells.
Connecting tissue holding the lobules – A fine, dense and irregular fibroelastic connective tissue layer holds these lobules together. This layer extends from Glisson’s capsule – the fibrous capsule covering the entire liver. This tissue extends into the structure of the liver and accompanies the blood vessels, ducts and nerves at the hepatic hilum.
Peritoneal Layer – A serous coat derived from peritoneum covers the whole surface of the liver with the exception of ‘bare area’. This layer firmly adheres to the inner Glisson’s capsule.
Lobes of Liver
As viewed from above – the liver is grossly divided into a right lobe and a left lobe by falciform ligament.
As viewed from below – the liver is divided into four parts i.e. –
– Left lobe
– Right lobe
– Caudate lobe
– Quadrate lobe
Caudate and Quadrate lobes are located between the right and left lobes.
Ligamentum venosum and round ligament of the liver further divide the left side of the liver in two sections.
Porta Hepatis divides the left portion of the liver into four segments.
Surfaces of the Liver
a. Diaphragmatic Surface – The upper surface of the liver, which includes the convex upper areas of both the right and left lobes accommodating the shape of the diaphragm, is called a diaphragmatic surface. It has a triangular ‘bare area’ which is in direct contact with the diaphragm. The other part of the upper surface, other than the bare area, is covered by Peritoneum – a double layered membrane.
The same peritoneum folds on itself so as to form the falciform ligament and the right and left triangular ligaments. Falciform ligament attaches the liver to the posterior portion of the anterior body wall. The triangular ligaments do not have any functional importance.
b. Visceral surface – The inferior surface of the liver is called the visceral surface because it is in contact with visceral organs of the abdomen. This surface is concave and uneven. This area is also covered by peritoneum with the exception of those areas where it attaches to the gallbladder and porta hepatis.
To the right of the quadrate lobe is the fossa of gallbladder. The gallbladder along with its cystic duct occupies this fossa, near to the right end of porta hepatis.
Impressions of the liver
Impressions are formed on the under surface of the liver where it comes into contact with various adjacent structures and visceral organs. Below mentioned are the impressions –
– Colic impression – for hepatic flexure of the colon (right lobe)
– Renal impression – for part of right kidney and part of suprarenal gland (right lobe)
– Suprarenal impression – for right suprarenal gland (right lobe)
– Duodenal impression – medial to the renal impression, for descending portion of the duodenum (right lobe)
– Gastric impression and tuber omentale – for stomach (left lobe)
Microscopic Anatomy of the Liver
Each lobe of the liver is made up of hepatic lobules. These lobules are hexagonal in shape. They consist of hepatocytes and sinusoids radiating from a central vein.
Portal Triad – It is a distinct component of a lobule. It consists of three components i.e. the hepatic artery, the portal vein and common bile duct. Each triad runs along each of the lobule’s corners.
Liver Cells – There are two major types of liver cells.
– Parenchymal cells / hepatocytes make up about 70-85% of liver volume
– Nonparenchymal cells – make up about 40% of liver cells but only 6.5% of liver volume
Other cells include –
– Sinusoidal endothelial cells and Phagocytic Kupffer cells – line the liver sinusoids
– Hepatic stellate cells (nonparenchymal) – found in perisinusoidal space
– Intrahepatic lymphocytes – present in the sinusoidal lumen
Functional Anatomy
The Porta Hepatis is an opening present in the hepatic hilum (the central area). It carries the common bile duct and common hepatic artery and the opening for the portal vein.
Functional left and right lobes – are the areas of liver supplied by the left and right branches of the bile duct, hepatic vein and portal vein. Cantlie’s line is an imaginary plane which separates the functional lobes of the liver.
The true right and left lobes of the liver are demarcated / separated by Cantlie’s line and middle hepatic vein.
The right hepatic vein divides the right lobe into anterior and posterior segments.
The left hepatic vein divides the left lobe into the medial and lateral segments.
Further the Couinaud System of classification divides the liver into eight functionally independent liver segments, each of which having its own vascular inflow, outflow and biliary drainage.
Fetal Blood Supply
Umbilical vein, which supplies nutrients to the growing fetus, is the major source of blood to the liver.
Functions of Liver
It is estimated that the human liver is responsible for over 500 different functions in the body which are mainly carried out by the liver cells known as hepatocytes.
Blood Supply to the liver
The blood supply to the liver is derived from both the hepatic portal vein and hepatic arteries. The hepatic portal vein is the main gamechanger here. It supplies around 75% of blood supply to the liver. It also carries the venous blood drained from the spleen, gastrointestinal tract and its associated organs. The arterial blood supplied to the liver comes from hepatic arteries which forms the other 25% of blood supply.
The blood flows through the liver sinusoids and empties into the central vein located in each lobule.
On the other hand, the central veins coalesce into hepatic veins. These veins leave the liver and drain into the inferior vena cava.
Biliary Tract or Tree
It is the pathway by which the bile which is secreted by the liver is transported to the duodenum, the first part of the small intestine. The tract is derived from the branches of the bile ducts. The bile collects in the bile canaliculi. These canaliculi radiate to the edge of the liver lobule. Here, they merge to form bile ducts. These ducts are called intrahepatic bile ducts while they are within the liver but are called extrahepatic bile ducts once they exit from the liver. The intrahepatic ducts drain into right and left hepatic ducts. These ducts exit the liver and merge to form the common hepatic duct. The common bile duct is formed by the joining of the common bile duct exiting the liver and cystic duct coming from the gallbladder.
The common bile duct drains the bile directly into the duodenum or it is stored temporarily in the gallbladder via the cystic duct.
Ampulla of Vater / Hepatopancreatic Ampulla – It is present in the second part of the duodenum into which the common bile duct and the pancreatic duct enters and opens into the duodenum.
Liver transplantation was first performed by
– Thomas Starzl – USA – IN 1963
– Roy Calne – Cambridge, England – 1967
It is the only option for those with irreversible liver failure. Most liver transplants are done for chronic liver diseases leading to Cirrhosis.
In Ayurveda, the liver is called Yakrit. Ayurveda too has mentioned the liver as a right sided organ located in the abdominal cavity.
Yakrit, along with Pliha – spleen and Raktavahini Dhamanis – arteries carrying blood, is the root of raktavaha srotas – channels forming and carrying blood in the body. They are also the seat of raktadhara kala – membranes and layers within the pulp of the liver which help in formation of good quality and quantity of blood.
Also, the liver and spleen are considered as ‘raktashaya’ i.e. reservoirs of blood in the body. Modern anatomy too considers the same.
Functionally the liver and spleen are the abodes of ranjaka pitta – a pitta subtype which helps in colouring the rasa tissue entering these organs and transforming it into rakta – blood tissue.
Related Reading – Yakrit Rachana Shareera – Anatomy of liver, Ayurveda perspective
