Function of the liver in human body – Understanding how does liver works
- What is the anatomy and physiology of the liver?
- How does blood flow through the hepatic portal system?
- What is the function of the liver in the human body? And, how does the liver works?
- 1. Filtration of blood
- 2. Exocrine function (helps in digestion)
- 3. Endocrine function (produce essential proteins)
- 4. Metabolic function
Today, we are going to understand the anatomy and function of the liver.
Although every organ has its own function and importance. But the liver plays a versatile role that has numerous functions.
Whatever you eat in your daily life, it has an incredible journey from your mouth to anus. The food travels in your entire food pipe or gastrointestinal tract.
It is digested by the stomach and intestine, then absorbed into the blood, and finally goes to the liver. The liver is responsible for managing your food.
Here, you will understand the importance of the liver. Let’s start from the basics –
What is the anatomy and physiology of the liver?
The liver is the heaviest organ and largest gland of your body which is around 1.5 kg weight. This organ is covered with a capsule of Glisson, which is made up of connective tissue.
The liver is roughly triangular, and it is located just below the diaphragm and above your stomach. It is present on the right side of your abdomen.
You usually can’t feel the liver because most of the portion is covered with the ribcage. Your liver is connected with the hepatic artery and hepatic portal vein.
How does blood flow through the hepatic portal system?
Hepatic portal circulation pathway –
Generally, your heart (aorta) delivers oxygenated blood (pure blood) to various organs like the spleen, pancreas, and GIT (Gastrointestinal tract).
After delivering oxygenated blood to these organs, the blood becomes less oxygenated. Then these splenic and mesenteric arteries are fuse together and make the portal vein.
This portal vein is connected with the liver.
A portal vein brings more blood to the liver but is less oxygenated. But there is another artery that provides oxygenated blood to the liver by a hepatic artery connected with the aorta.
This hepatic artery brings less blood to the liver but is more oxygenated. In the liver, there are two input systems – portal vein and hepatic artery
Credit – T Sheasby, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons.
Generally, the liver is decorated with around 1 million lobules, and each lobule is a hexagonal shape. The portal vein and hepatic artery connect with each corner of the lobules in the liver.
There are portal triads at each corner of the lobule (portal vein, hepatic artery, and bile duct). Later on, this area is called portal tetrad because it is also connected with the lymph vein. So, it simply says the portal area.
The liver cell contains a tube-like structure called a sinusoidal capillary. It is well arranged as a railway track. These sinusoidal capillaries connect with every portal area to a central vein (center) of the lobule. These capillaries are very fenestrated or highly porous.
Credit – 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 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons
These sinusoids are made up of discontinuous endothelium, and along with that, they are lined with Kupffer cells which are macrophages (ingest harmful foreign particles)
The blood plasma moves from the periphery to the central vein of the lobule, called centripetal flow (outward to inward).
Due to the highly porous capillary of sinusoids – blood comes and drains back. This process happens in the space of Disse (perisinusoidal space) in between sinusoids and hepatocytes.
By this process, the liver delivers toxin-free blood by a hepatic vein which backs into the circulation and is connected to the inferior vena cava (right side of the heart).
But some blood does not come back; it goes in the form of lymph and flows outward.
So, the liver also has two output systems – hepatic vein and lymphatic vessels.
What is the function of the liver in the human body? And, how does the liver works?
The liver is such a vital organ with a lot of function that works 24 hours a day. Generally, there are four primary functions of your liver. Let’s discuss each in detail –
1. Filtration of blood
The main work of your liver is to filter blood and detoxify the toxins. It helps clean and purify your blood, which carries nutrients and comes from different organs-like GIT, spleen, and pancreas.
Your liver deals with foods, drugs, alcohol, and other toxins. All these things (or deoxygenated blood) pass through the liver by the portal vein, and it detoxifies by liver components.
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 signaling molecules protect from toxins and help in the detoxification of 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.
2. Exocrine function (helps in digestion)
Your liver has many functions, but its primary job is during digestion. Your liver has an exocrine function. In other words, it does not release into the bloodstream.
It mainly secrets the bile and its components outside the liver.
Liver secrets five main components of bile –
- Bilirubin (mainly conjugated with glucuronic acid in hepatocytes)
- Phospholipids and lecithin
- Bile acids or salts (cholic acid and chenodeoxycholic acid)
- IgA antibody (release into GIT and protect the GIT from bacteria, virus, and other invading organisms)
Around 80% of your liver is well decorated with hepatocytes (liver cells). These hepatocytes are arranged in a single sheet in between the space of two sinusoids.
These hepatocytes make bile and secrete bile from the center to the periphery (inwards to outwards) in lobules called centrifugal flow.
Generally, the hepatocytes secrete bile towards biliary canaliculi (grove or gap in hepatocytes) and come into the bile duct of lobules.
Then these bile ducts from every corner of lobules come together and form the left hepatic duct and right hepatic duct. After that, these hepatic ducts fuse together and become a common hepatic duct outside the liver.
Meanwhile, a cystic duct of the gall bladder (pear shape organ) joins the common hepatic duct.
This common hepatic duct and cystic duct fuse together, which makes the common bile duct. Eventually, the common bile duct is fused with the pancreatic duct and release into the duodenum.
Here, the gall bladder acts as a reservoir that helps in the storage of your bile. Usually, the gall bladder is full before a meal, but after a meal, it becomes empty.
Bile has a vital function in the digestion and absorption of fat- and fat-soluble vitamins.
So, it is one of the primary function of the liver in the digestive system.
3. Endocrine function (produce essential proteins)
Your liver also works as an endocrine function. Endocrine means release chemical substances directly into the bloodstream.
Hepatocyte has a lot of Golgi apparatus which help to make certain protein for blood.
a. Albumin– This is the main protein of your blood plasma that helps to maintain colloidal osmotic pressure in blood plasma. Simply say, it helps keep your fluid in the bloodstream so that it could not leak into other tissues.
Albumin is a major plasma protein around 55%. It also acts as a carrier that transports lipid and steroid hormones.
b. 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.
c. Coagulation factors– fibrinogen, prothrombin, etc. They help to control bleeding.
d. Lipoproteins– They help to transport fat molecules. Lipoproteins are present in the form of VLDL (Very low-density lipoprotein), LDL (low-density lipoprotein), and HDL (High-density lipoprotein).
- VLDL contains more triglycerides, some cholesterol, and less protein. It helps delivered triglycerides to the cell in your body.
- LDL contains more cholesterol and protein, which are responsible for carrying cholesterol to the cell. Sometimes it is also called bad cholesterol because it deposits cholesterol on the wall of arteries and produces a cardiovascular problem like ischemic heart disease.
- HDL contains less cholesterol and more proteins. It helps in carrying cholesterol from cells back to the liver. So, it is also called good cholesterol.
4. Metabolic function
The liver also plays an essential role in metabolism.
a) Stabilizing blood glucose level
It acts as a blood glucose reservoir. If you have a high blood glucose level, it converts blood glucose into glycogen form called glycogenesis.
Whenever your blood glucose level falls, the liver breaks down the glycogen into glucose called glycogenolysis.
It also helps in the formation of gluconeogenesis in low blood glucose. This means it makes glucose from a non-carbohydrates source like – amino acid and fatty acid.
b) Biotransformation of drugs
The liver is one of the organs which deals with the drugs. In the liver, the hepatocyte has a lot of peroxisomes which help in biotransformation.
Most of the drugs are metabolized into hepatocytes and alter the inactive drug (prodrug) into an active form called biotransformation.
Many drugs are conjugated with glucuronic acid in the hepatocytes, and then they go back into the blood.
c) 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.
d) Urea formation
Every day you consume many proteins in your life in the form of meat, dairy products, eggs, fish, etc.
Your body breaks down protein into amino acids. The rest of it converts nitrogen which should be removed from your body.
The liver helps to change nitrogen into urea by the urea cycle. By this process, urea eliminates from your body in urine form.
Your liver is an essential organ of your life; it deals with bad food, good food, and various toxins. If your liver stop working, you may face so many problems.
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.
I hope you gathered a lot of information from this post on the function of the liver, and it will be helpful for you.
1. The liver.