Structure and functions of liver

Introduction

The liver is one of the most important vital organs and is the largest gland in our body. It weighs approximately 3 pounds, however, factors such as age, body weight and disease conditions can influence the size. By percussion, the average size of the liver is 7.5 cm for females and 10.5 cm for males. If the liver span is 2 to 3 cm larger or smaller than the normal value,  liver disorders can be suspected. Furthermore, it is a cone-shaped organ appears dark reddish-brown encased in a protective fibro-elastic sheath known as ‘Glisson’s capsule. Our liver is one of the most important organs without which we cannot survive. This is due to the fact that the liver is the fundamental organ of detoxification. Detoxification helps in purifying our body from many toxic substances such as harmful drugs, alcohol, and poisons. However, it is just the tip of the iceberg because the liver performs many other functions directly or indirectly.  Hepatology is the term used for the branch of medicine that deals with the disorder of liver, gallbladder, biliary tree, including the pancreas.

 

 

Location

Our liver is situated in the upper right quadrant of the abdominal cavity, just beneath the diaphragm. On top of the liver, parts of the stomach, right kidney, and intestines are present. On the lower surface of the liver, organs like gallbladder, pancreas and a part of the intestines are found. These organs join the liver for the digestion and absorption of food. The liver is attached to the abdominal wall and a portion of it touches the diaphragm via 5 peritoneal ligaments. These ligaments support most of the abdominal organs including the liver. They are; falciform ligament, the coronary ligament, 2 lateral ligaments, and the ligamentum teres hepatis. The endocrinal organ is partly protected by the hard bony rib cage. While examining the liver, it is important to locate the lowest rib on the right upper quadrant where the right lower border of the liver is felt.

 

 

 

 

 

 

 

Macro anatomy of the liver

For the ease of understanding, the liver is anatomically divided into lobes. From the top view, the liver appears bilobed, the left and right lobes which are separated by the falciform ligament along with the middle hepatic vein.  The right lobe of the liver is 6 times larger than the left lobe despite both of them perform almost the same function. From the inferior angle (from below), the meaty organ appears to be 4-lobed and a bit larger, i,e the left lobe, right lobe,  quadrate lobe and the Caudate lobe. However, the organ is scientifically divided into 2 principal lobes, right and the left lobes.  The right Lobe covers the bulk of hepatic tissue and it is separated from left lobe by a main lobar fissure. The dorsal surface of the left lobe is separated from caudate lobe wi the help of ligamentum venosum and proximal left portal veins.  The medial segment makes up the quadrate lobe. The caudate lobe is located posterior to the porta hepatis, between ligamentum venosum and inferior vena cava. Our abdomen and the liver is thinly segregated by a membrane called the peritoneum. The peritoneum is the covering layer of all the abdominal organs which provides a protective shield. It also helps in the segmentation of abdominal organs from the back and vertebral column. The peritoneum is subdivided into 2 main layers in which the visceral layer sits close to the surface of the liver while parietal sits just above the visceral layer. As the liver is surrounded by a number of organs, they form many impressions, some of which includes gastric impression, renal impression, suprarenal impression, colic impression, and the duodenal impression. Our Liver receives nutrients from the haptic artery and portal vein. The portal triad makes up the portal vein, hepatic artery and the common bile duct helps to carry oxygen in addition to the major carrier hepatic artery. Portal Veins receives blood from bowel to liver and they carry.  Hepatic veins help to drain the blood from the liver to the inferior vena cava.     

 

 

 

Liver and its surrounding organs

 

 

 

Microscopic anatomy of liver

Unlike other organs, our liver is supplied by the 2 two major sources of blood including portal and the hepatic channels. The hepatic artery is connected to the major abdominal aorta that brings pure blood from the heart. The impure blood is removed from the liver with the help of 3 hepatic veins. The portal circulation is the major channel of the liver`s supply because of multiple capillaries and veins that supply blood from in and out of the liver. At the microscopic level, the liver can be divided into a number of hepatic lobules.  Each lobule resembles a  hexagonal mass made up of plates of hepatocytes. Hepatocytes are called the liver cells,  joins the central vein that carries blood out of the liver. If we analyse the microscopic anatomy of the liver, we can observe 2 major types cells; parenchymal cells and the non-parenchymal cells. About 75%  of the liver is supplied with the parenchymal hepatocytes while 25% is made up of non-parenchymal cells. Human liver contains sinusoids, bead-like cells pared in a chain.  Sinusoids are lined with sinusoidal endothelial cells and phagocytic Kupffer cells. Furthermore, hepatic stellate cells, a type of non-parenchymal cells,  found alongside perisinusoidal space which is located between a sinusoid and a hepatocyte. Intrahepatic lymphocytes are found inside the sinusoidal lumen.

 

 

 

 

 

 

Functions of the liver

The liver is a multifunctional organ works in close connection with almost all the body systems. Apart from its principal duty, detoxification,  our liver performs about 500 distinct roles. Some of them are as under.

 

Detoxification

Detoxification is one of the major function of the liver in which the liver cells work by identifying and breaking the dangerous molecules that enter into our body. The end products after the toxins being destroyed are pushed into the kidneys through renal circulation.  Majority of the toxic poisons, drugs, alcohol and many other harmful substances are stabilized by the liver cells.

 

Bile production

Bile is one of the important digestive juices produced by hepatocytes. The juice is directly drained into the duodenum- the first segment of the small intestine through the bile duct. Bile juice helps in breaking down the complex lipids into simple molecules while it also plays a pivotal role in regulating the bilirubin levels, which are the bile pigments necessary for many functions in our body.  Furthermore, bile secretions from the liver keep a check on the level of cholesterol which is quintessential for health and fitness. Additionally, bile is mixed with a number of electrolytes and water.

 

Blood clotting

Bile juice contains vitamin-K, essential for the production of clotting factors, coagulants. Timely release of coagulants blocks bleeding from any part of the body hence, the clotting factors released by the liver are called natural clotting factors. If the liver fails to produce enough bile, a person can suffer profuse bleeding and hypovolemic shock which can undoubtedly cause death.

 

Fat metabolism

The liver is a primary organ for the storage of lipids,  hence it is a natural regulator of the cholesterol levels in our body. The abnormal liver function causes faulty fat metabolism, consequently, there is a rise in  HDL (high-density level) cholesterol. Moreover, the liver is a great reservoir of fat-soluble vitamins, ADEK necessary for many functions in our body. 

 

Carbohydrate metabolism

Although the liver is not the primary regulator of carbohydrate metabolism, some of the enzymes present in the liver help in the glycogenesis (production of new glucose molecules) to boost the body`s energy levels. It also aids in glycolysis; a process where the glycogen is broken down into glucose to supply energy when our body demands it. 

 

Protein metabolism

The complex proteins are converted into simple amino acids in the presence of bile juice where ammonia is a by-product of the process.  The liver also help in the synthesis of non-essential amino acids. Hepatocytes help to produce most of the plasma proteins including albumin, and globulin which essentially works as blood proteins. Furthermore, albumin helps in the production of many antibodies necessary for its defence. The bile juices secreted by the liver also aids in the transportation of fatty acids and steroid hormones.

 

Synthesis of angiotensin

Angiotensin is one of the factors responsible for the regulation of blood pressure, the factor works by vasoconstriction (constricting the inner lumen of blood vessels) which allows the arteries to maintain optimal pressure required for the proper circulation of blood.

 

Immunological function

The liver participates in the mononuclear phagocytosis with the help of Kupffer cells. Liver involves in the induction of immune tolerance, strong innate immunity, and hematopoiesis.

 

 

 

Read more

1.    

Digestion and absorption

2.

Structure of respiratory tract

3.

Structure and functions of pancreas

4.

Anatomy and physiology of stomach

 

 

 

Questions

  1. What is the primary role of liver

  2. Explain the storage function of the liver.

  3. Describe the anatomic location of liver

  4. Explain the lobes of the liver.

  5. Describe the different cell-types in the liver.

  6. Explain the different functions of the liver.

 

 



img-1


img-1


img-1

Course List