Anatomy, Histology and Function of the Liver in Human Body

Posted On May 17, 2020April 5, 2023

Introduction

Want to know about the function of the liver in the human body?

Although every organ has its own function and importance, like – 

• Your heart pumps blood
• Your kidney works as a filter
• Your stomach helps in digestion
• Your lungs help in respiration 
• Your brain controls and coordinates every part of your body 

But what about your liver?

You will be shocked to know that there are 500 functions of the liver in our body. 

Well! The liver plays a versatile role in the human body.

Your liver has a lot of functions, such as digestion, metabolism, detoxification, filtration of blood, producing essential proteins etc. 

But do you know the primary function of the liver?

The primary function of the liver is the production and secretion of bile.

In this post, you will learn about numerous functions of the liver. But before this, we have to know about liver histology, anatomy, and physiology.  

Let’s start from the basics –

Human liver anatomy and physiology 

The liver is the heaviest organ and largest gland of your body which is around 1.5 kg weight.

Your liver is covered by Glisson’s capsule, made of white fibrous connective tissue. 

Basically, the liver is an intraperitoneal organ that presents within the peritoneal cavity. You can’t feel the liver because most of the portion is covered with the ribcage. 

Shape of liver

Your liver is roughly triangular (cone) or wedge-shaped (looks like a pillow). It also looks half-moon or sickle-shaped. 

Size of liver 

The normal size of the liver is 6-12 cm (2.4 to 4.7 inches, or 60 to 120 mm), but the size of the liver may vary with age, sex, height and weight. 

Position of liver 

Regarding the position of the liver, it is located just below your diaphragm and above your stomach. It is present on the right side of your abdomen. 

Colour of liver

The normal colour of the human liver is generally reddish-brown.

Lobes of liver

The liver consists of two main lobes – the right lobe (larger lobe) and the left lobe (smaller lobe). A gallbladder is present below the right lobe of the liver. 

These two liver lobes are divided by falciform ligament. 

The liver’s right lobe is divided into a caudate and a quadrate lobe. Therefore, your liver has four lobes. 

Liver anatomy segments

Anatomically, your liver is generally divided into 8 segments. These are – 

• Segment 1 – Caudate lobe is located posteriorly 
• Segment 2 – Posterior and superior section of the left lobe 
• Segment 3 – Anterior and inferior section of the left lobe 
• Segment 4 – Superior and inferior section of the falciform ligament 
• Segment 5 – Anterior and inferior section of the right lobe
• Segment 6 – Posterior and inferior section of the right lobe
• Segment 7 – Posterior and superior section of the right lobe
• Segment 8 – Anterior and superior section of the right lobe

Liver histology

Liver histology is a microscopic study of the liver. 

Let’s see a closer look at your liver.

If we take a section view of the liver. As we know liver is divided into lobes. Each lobe contains thousands of lobules, and each lobule has millions of cells called hepatocytes.

A liver is a structural and functional unit of hepatic lobules because our liver is well decorated by millions of hepatic lobules. 

If we see the microscopic structure of the liver lobule, it is a hexagonal shape. 

This hexagonal liver lobule contains 6 corners, and every corner of the lobule has 3 drainage systems or tubes, including –

• a branch of the hepatic artery (carries oxygenated blood from the heart),
• a branch of the hepatic portal vein (carries deoxygenated blood from the intestine)
• an interlobular bile duct (drain bile outside into the intestine)

This hepatic artery brings less blood to the liver but is more oxygenated. 

While the hepatic vein carries more nutrient-rich blood to the liver but is less oxygenated. This is called hepatic portal circulation flow.

A hepatic portal system is a vascular connection between the digestive tract and the liver. This system delivers nutrient-rich blood from the stomach, intestine, and spleen to the liver. 

The hepatic portal vein and hepatic artery are two input systems of our liver.  

Moreover, bile drains into the intestine through the bile duct. 

These three structures (hepatic artery, hepatic vein, and bile duct) are composed of a portal triad. Later on, this area is called portal tetrad because it is also connected to the lymph vein. So, it simply says the portal area.

A liver lobule contains a tube-like structure called a sinusoidal capillary. The blood from the portal triad travels into this liver sinusoids and goes to a central vein. 

To protect from microbes, some Kupffer cells (natural killer cells) are present within each liver sinusoid. 

Liver sinusoids are well arranged like a railway track. You must have seen many stones alongside the railway track.

Similarly, hepatocytes are well arranged alongside liver sinusoids like stones nearby a railway track. 

Liver sinusoidal capillaries are connected with every portal area to a central vein (centre) of the lobule. 

These sinusoids are very fenestrated or highly porous.

Due to the highly porous capillary sinusoids – blood comes and drains back. This process happens in the space of Disse (perisinusoidal space) between sinusoids and hepatocytes.

Through this process, the liver delivers toxin-free blood. 

This toxin-free blood goes into the circulation, which is connected to the inferior vena cava (right side of the heart). 

Bile flow pathway in the biliary duct system

We have seen how hepatocytes are parallelly arranged with liver sinusoids. 

The major work of our hepatocytes is to produce bile. It also helps in metabolism, detoxification, and protein synthesis.

Now, Let’s see how bile flows from the liver to the duodenum through a duct system. 

After synthesizing bile, hepatocytes (or liver cells) secrete bile. This bile flow travels into hepatic ducts (a tube-like structure where fluid flow). 

There are two hepatic ducts – the right and left hepatic ducts. 

The right hepatic duct drains bile from the right lobe of the liver, whereas the left hepatic duct drains bile from the left lobe of the liver.

The right and left hepatic ducts are joined outside the liver to form a common hepatic duct. 

This common hepatic duct starts to join with the cystic duct that comes from the gallbladder (helps in the storage of bile).

Later, the common hepatic and cystic ducts combine to form a common bile duct. 

After that this common bile duct fuses with the pancreatic duct to form the hepatopancreatic duct. 

This hepatopancreatic duct makes a small round vessel called Ampulla of Vater.

This ampulla contains a muscular valve called Sphincter of Oddi that controls the flow of bile and pancreatic juice. 

Eventually, bile drains into the duodenum. This bile helps in the digestion of fat in your intestine. 

Top 10 functions of the liver in the human body 

Your liver cells or hepatocytes are responsible for many functions of the liver.

It is believed that the liver performs more than 500 different functions, usually in conjunction with other body systems.

Here, we will discuss only the major functions of the liver.

1. Function of the liver in the digestive system

The liver has a primary function in your digestion. 

Your liver generally acts as an endocrine gland. Here, Liver cells help produce bile but do not release it into the bloodstream. 

Your liver also has an exocrine function. This bile is secreted outside the liver and released into your duodenum. 

If you take a fatty meal and this bile component help in the digestion of your fat. It breaks the fat into fatty acid and glycerol. 

In other words, it converts the big fat molecule into tiny fat molecules by emulsification.  

Fat absorption is carried out by bile salts because they act as an emulsifying agent or natural detergent. It increases the surface area of fat molecules that enhance enzymatic activity. 

Bile comprises water (95%) and solid bile constituents (5%). There are five main components in the composition of bile – 

2. Function of the liver in bilirubin metabolism

The liver also has a significant role in the metabolism of toxic bilirubin. 

Bilirubin is generally a component of bile juice but has no specific function. 

It acts as a bile pigment and gives a yellow colour to bile. 

Bilirubin is a waste product of your red blood cells or haemoglobin‘s destruction. 

Let’s see how?

Your red blood cells (RBCs) average life span is 120 days. After 120 days, RBCs have to be destroyed. 

These cells go to your spleen. Here, the spleen is a lymphatic organ that plays a vital role in destroying old RBCs by phagocytosis. That’s why spleen is also known as the “Graveyard of RBC”.

Red blood cells contain haemoglobin. It gets breakdown into “heme” and “globin”. 

This heme converts it into biliverdin and then eventually converts into bilirubin with the help biliverdin reductase enzyme. 

Red blood cells

↓

Haemoglobin

↓

Heme + globin

↓

Biliverdin

                       ↓biliverdin reductase

Bilirubin

If we simply say, bilirubin is a breakdown product of haemoglobin. 

This bilirubin is very toxic because it is lipid soluble (or non-water soluble) and unconjugated. 

Bilirubin must be water soluble to excrete quickly from your body. 

So, bilirubin goes to your liver for conjugation. The liver helps in the metabolism of bilirubin. It converts the unconjugated bilirubin into conjugated bilirubin by glucuronidation. 

This conjugated bilirubin is less toxic, more polar and water-soluble. 

After converting unconjugated bilirubin into conjugated form, this conjugated bilirubin goes to the small intestine (duodenum) by the bile duct. 

Then it goes to the large intestine, and it gets oxidized by some bacteria that convert into urobilinogen. 

Urobilinogen is a final bilirubin product that excretes from the body through urine and faces. 

3. Role of the liver in deamination and urea production

This is another crucial function of the liver to remove the toxic product (e.g., ammonia) from the body. 

We have three essential bio-molecules – carbohydrate, lipid and protein. 

We eat carbohydrates and lipids that get converted into glucose. Our body utilizes glucose as per requirement, and the excess glucose gets stored in the liver in glycogen or fat form.

As far as protein is concerned, when we eat this food, it gets utilized in tissues but does not store in the liver. 

Protein contains various amino acids. Each amino acid has an amino group in its structure. 

After utilising the amino acid in tissues, it goes to the liver for metabolism. 

Here, our liver breaks the protein molecules to prevent returning to tissues. It removes the amino group from the amino acid and converts it into ammonia. This process is called deamination. 

This deamination process produces a lot of ammonia (NH₃). If too much ammonia accumulates in the body, it would be a highly toxic compound for our brain. 

Therefore, our liver cells (hepatocytes) help to convert the ammonia into urea. This type of conversion occurs in the Urea cycle, and the process is called detoxification. 

Eventually, the liver converts the toxic compound (ammonia) to a non-toxic compound (urea), and it easily removes from urine. 

4. Function of the liver in glucose metabolism

The liver also plays an essential role in carbohydrate metabolism. 

What we eat in carbohydrates converts into glucose and then goes to the liver. 

Here, the liver plays a vital role in glucose metabolism and stabilising blood glucose levels.

The metabolism of glucose is done by the liver via two processes – anabolism and catabolism.

In glucose anabolism, the liver converts the excess glucose into glycogen. This process is called glycogenesis. It works as glucose storage. 

While in glucose catabolism, your liver breaks down the glycogen into glucose. This process is called glycogenolysis. This glycogenolysis process starts to work whenever you have low blood glucose in your body. 

When your body does not have sufficient glucose. In that case, your liver makes glucose from non-carbohydrates sources (e.g., amino acids and fatty acids). This process is called gluconeogenesis. 

Therefore, the glucose metabolism pathway is known as glycogenesis, glycogenolysis and gluconeogenesis. 

5. Function of the liver in lipid metabolism 

In our body, lipids (or fat) are stored in adipose tissues as triglycerides (also called triacylglycerol).  

Triglyceride is a second source of energy. Whenever we have a deficiency of glucose, then this triglyceride converts into energy. 

In adipose tissue, triglyceride converts into glycerol and fatty acid. This process is called Lipolysis.

Triglyceride → Glycerol and fatty acid

Here, glycerol directly goes to liver cells (or hepatocytes) for metabolism. It reaches the cytoplasm and enters the Glycolysis pathway via glucose-6-phosphate.

Later, pyruvate converts into Acetyl CoA and enters Citric Acid Cycle (Kreb’s cycle) in mitochondria. Eventually, it produces energy in the form of ATP by ETC (Electron Transport Chain). 

On the other hand, fatty acid gets oxidised (or degraded) by the Beta Oxidation process. It is generated Acetyl CoA and enters the citric acid cycle. Eventually, produce energy in the form of ATP.

Suppose you eat a lot of carbohydrates, which convert back into fat. 

In this condition, glycerol and fatty acids are converted into fat (triglyceride), called Lipogenesis. This lipogenesis process mainly occurs in the liver and adipose tissue.

Glycerol and fatty acid → Triglyceride

In Lipogenesis, glycerol-3-phosphate from the glycolysis pathway converts into glycerol, called Glycerol synthesis. While acetyl CoA converts into fatty acid is called Fatty acid synthesis. 

The liver is also a hub in the production of cholesterol. The process of formation of cholesterol from Acetyl CoA is called Cholesterol Synthesis.

Cholesterol is essential in forming steroid hormones, cell membranes and the composition of bile. 

In emergency situations or starvation, the liver also produces ketone bodies from Acetyl CoA. This process is called Ketogenesis. 

To get the energy from ketone bodies, it converts ketone bodies to Acetyl CoA and enters Krebs’ cycle. This is called Ketolysis. 

Moreover, the liver helps lipoprotein synthesis that circulates throughout the body via the blood. 

There are five types of lipoproteins – CMs, VLDL, LDL, IDL and HDL.

6. Role of the liver in drug metabolism

The liver has a vital role in drug metabolism.

When you take medicine orally, it does not directly go to your bloodstream. Before entering your main systemic circulation, medicine has to go through the liver via hepatic portal vein. 

Since liver generally receives all the blood by hepatic portal circulation that comes from the stomach and intestine. So, before distribution, the medicine metabolizes first in the liver. It is called First Pass Metabolism (FPM). 

After FPM, it enters your main blood circulation.

Once the drug has done its action, a medicine has to clear out from the body. But it is difficult for the kidney to eliminate lipophilic (or lipid-soluble) drugs from the body.

So, medicine comes back into blood vessels from tissues. 

After returning to the blood, medicine goes to the liver for biotransformation. Here, lipid-soluble drugs (non-polar) convert into water-soluble (polar) drugs. This is called the metabolism of a drug. 

Your liver metabolizes the medicine in two phases – Phase 1 and Phase 2 reactions.

To know the complete metabolism of the drug, Click here

7. Role of the liver in production of essential blood proteins

Our liver also works as an endocrine function. Endocrine means the release of chemical substances directly into the bloodstream.

Hepatocyte has a lot of Golgi apparatus, which help to make certain proteins for blood.

• Albumin– This is the main protein of your blood plasma that helps to maintain colloidal osmotic pressure in blood plasma. This means it helps keep your fluid in the bloodstream to prevent it from leaking into other tissues. Albumin is a major plasma protein, around 55%. It also acts as a carrier that transports lipid and steroid hormones.
• Globulins– They are present in blood plasma in four categories: alpha 1, alpha 2, beta, and gamma. They help in fighting infection and blood clotting.
• Coagulation factors– fibrinogen, prothrombin, etc. They help to control bleeding.

8. Function of the liver in detoxification 

Your liver also has a key role in detoxification. It filters your nutrient-rich blood and detoxifies the toxins. 

Generally, your liver deals with foods, drugs, alcohol, and other toxins. 

All nutrient-rich blood (or deoxygenated blood) passes through the liver by the portal vein that comes from different organs-like GIT, spleen, and pancreas.

They all get detoxified via liver cells.

Your liver cells (or hepatocytes) help clean and purify your deoxygenated blood.  

Here, Kupffer cells play an essential role in the filtration of blood. It is activated when it senses toxins (like bacteria, virus, dead cells, or other toxins) and release cytokines, Reactive oxygen species (ROS), Nitric oxide (NO) etc.

These cells signalling molecules protect from toxins and help detoxify your blood. Eventually, the liver provides toxin-free blood through a hepatic vein.

Your liver cells also contain many lysosomes that help remove waste and prevent bacteria, viruses, or other foreign materials.

In this way, the liver helps to clean your blood.

9. Function of the liver in modification of Vitamin-D

Vitamin D comes to the liver in the form of cholecalciferol and converts it into 25-hydroxycholecalciferol. 

It is further hydroxylated by the kidney, which converts into 1, 25 -dihydroxycholecalciferol called calcitriol, which is the fully biologically active form.

Eventually, this calcitriol circulates in the blood, which deals with calcium and phosphorus.

10. Some other functions of the liver in the human body 

Your liver also has enrolled in some other crucial functions –  

• Lymph production
• Haemopoiesis formation of blood cells (RBC and WBC) in an embryonic stage 
• Formation of angiotensinogen hormone 
• Production of Vitamin A (retinol)
• Storage of fat-soluble vitamins (A, D, E, K) and Vitamin B12 water-soluble vitamin

Conclusion

Whatever you eat in your daily routine passes through the liver. 

Now you can think how the liver is an essential organ in our body. If your liver stop working, you may have serious health issues. 

In this post, we discussed anatomy, physiology, liver histology, bile flow pathway and important function of the liver in the human body. 

Your liver does hard work for you. So, this is your responsibility to keep your liver healthy.

Healthy food and exercise are the best way to keep your liver healthy.

If you found this post informative, please share this post on social media. 

FAQ 

Q 1. Which part of the alimentary canal receives bile from the liver?

The duodenum part of the small intestine receives bile from the liver.

Q 2. What is the liver’s biggest function? 

The primary and most prominent function of your liver is to produce bile. After making bile, it is secreted out from the liver via the bile duct and reaches the small intestine. This bile helps in the digestion of your fat via the emulsification process. 

Q 3. Can you live without a liver?

No. You would not be able to live without a liver. The liver is a vital organ, and it has a lot of crucial functions. Sometimes, liver transplants are required when your liver stops functioning properly.

Q 4. What are the 3 main functions of the liver?

The three most essential functions of the liver are – 

1. Production of bile
2. Detoxification of blood
3. Metabolism of carbohydrates, protein and lipid

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