The liver is the largest organ and at the same time the largest gland in the human body. It represents around the 2% - 5% of the total body weight in adults, having an average weight of 2 kg (1.8 - 2.1 kg in the females and 1.9 - 2.3 kg in males). 

Figure 1. The liver anatomy

The liver plays a major role in the metabolism of several molecules, including proteins and lipids. It is the principal body reservoir of the glycogen polymer that in turn can be degraded through a glycogenolysis process, into glucose, a rapidly available energy source for our brain. The liver synthetizes many plasma proteins, produces bile, which is necessary for the fats emulsion during the digestion, and it has an important role in the detoxification of toxic compounds derived from several metabolic processes or from diet. The organ is protected by the Glisson's capsule, consisting on a thin layer of connective tissue. The liver is a reddish-brown, wedge-shaped organ, however, in case of some liver disease, such as steatosis, it may turn into a more yellowish color, due to fat accumulation. When cirrhosis occurs the liver appears irregular with a fine and diffuse nodularity. 

The liver, can be grossly divided into four lobes: right, left, quadrate and caudate. Hepatic artery represent the principal oxygen-rich blood supplier for the liver.
In addition, the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas. Just before entering the hepatic parenchyma, the portal vein divides into the left and right branches
Another venous system of the liver consists of three hepatic veins draining the blood from the left, middle, and right parts of the liver directly into inferior venae cavae.

Figura 2. The Portal system. The hepatic portal system returns blood, rich in nutrients, from the digestive tract and spleen to the liver


The hepatic lobule is the functional unit of the liver, it has roughly hexagonal shape and consist of numerous trabeculae of hepatocytes, which radiate from a central vein towards an imaginary perimeter of interlobular portal triads. The portal triad, consists of the hepatic artery, the portal vein, and the common bile duct and run along each of the lobule's corners. Hepatocytes are the main cells of the liver, performing most of the metabolic functions of the liver. They represent the 80% of the liver volume and have a polygonal shape with large nuclei.

Figure 3. The liver lobule

From portal vein, the blood flows through sinusoids flanking hepatocytes. They are fenestrated capillaries surrounded by sinusoidal endothelia cells and the phagocytic Kupffer cells, that can release numerous molecules, including cytokines.

Microvilli originating from the hepatocytes extend towards the Disse space, which is a space separating hepatocytes from sinusoids. In addition, the Disse space is enriched in type I, III, and IV collagen and reticulin. Hepatic stellate cells are nonparenchymal cells found in the perisinusoidal space, between a sinusoid and a hepatocyte. They have a typical star-like shape and they have a major role in the secetrion of molecules constituting the extracellular matrix, such as collegen type III and reticulin. They are also involve in the liver regeneration since they produce growth factors enabling the cell proliferation.

Figure 4. Liver lobule cellular organization


The liver has multiple important functions in our body that can be grouped into three main areas:

  • Blood filtration and reservoir
  • Secretion
  • Metabolism

The liver serves as an important blood reservoir in case of rapid changes in blood volume, indeed it has a dynamic vascular system with a large capacitance and a very low venous resistance.

A well-known function is the production and secretion of bile, which has a role in fats emulsion when released into duodenum, the first tract of the intestine. Bile is accumulated in the gallbladder. The liver can synthetize glucose from amino acids, it has a role in the metabolism of some proteins and some important hormones, such as insulin. The liver produces numerous clotting factors as well as several plasma proteins, such as albumin.

The liver is the organ responsible for the synthesis of triglycerides and cholesterol. It is also part of the lipid trafficking system involving plasma lipoproteins, chylomicrons very low density lipoprotein (VLDL) and high density lipoprotein (HDL).

As previously mentioned, the liver has an important function in the production, accumulation and degradation of glycogen, in addition it accumulates vitamin B12iron and copper.

In the liver, haemoglobin is degradated into bilirubin that should be properly metabolized and eliminated. The accumulation of bilirubin can cause neonatal jaundice , which if prolonged can cause serious neuronal damages. The liver detoxificates several toxic compounds such as, ammonia, derived from protein metabolism, which is transformed into urea, alcohol, drugs, and others.  


The liver biology and pathobiology, 4th ed., Irwin M. Arias, 2001 Lippincott Williams and Wilkins

Trattato di Fisiologia medica, III ed., Arthur C. Guyton. 1987 Piccin.


Figure 1.. Modified from T Sheasby, CC BY-SA 3.0 , via Wikimedia Commons e BruceBlaus, CC BY-SA 4.0 , via Wikimedia Commons

Figure 2. Free license Pixabay

Figure 3. Hepatic_structure.png: Boumphreyfrderivative work: Adert, CC BY-SA 3.0 , via Wikimedia Commons

Figure 4 Originally by Frevert U, Engelmann S, Zougbédé S, Stange J, Ng B, et al. Converted to SVG by Viacheslav Vtyurin who was hired to do so by User:Eug., CC BY 2.5 , via Wikimedia Commons