Liver anatomy and physiology

Definitions & Key takeaways

The liver is an organ that lies just below the diaphragm in the right upper quadrant of the abdominal cavity. It has a wide range of functions, including metabolism, detoxification, production of proteins important for blood clotting, and bile production.

The liver consists of four anatomical lobes, which are the right, left, caudate, quadrate lobes. Lobes are further subdivided into segments, all the way down to the main functional unit of the liver called hepatic lobule. Hepatic lobules are small with a specific hexagonal shape and it consists of four main parts: the portal triad, hepatocytes, hepatic sinusoids, and central vein.

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Introduction0:00–0:19

Your liver lies just below your diaphragm in the right upper quadrant of your abdominal cavity. And it does a wide range of things - from helping to manage the body’s metabolism, detoxification, and bile production.

Ligaments0:19–1:10

The surface of the liver is covered by a serous membrane called the visceral peritoneum. The visceral peritoneum folds over on itself, and it suspends the liver from the abdominal wall and the diaphragm.
There are five of these peritoneal folds and they’re referred to as ligaments. There’s the falciform ligament, which attaches the liver to the anterior wall of the abdominal cavity.
There’s the round ligament of the liver, which is a fibrous cord found in the free margin of the falciform ligament. There’s the coronary ligament, which attaches the liver to the inferior surface of the diaphragm.
There’s the right triangular ligament, which is a small triangular fold which attaches the right lateral surface of the liver to the diaphragm.
And lastly there’s the left triangular ligament, which attaches the upper left surface of the liver to the diaphragm. Now, viewed from above, the liver is divided by the falciform ligament into two main lobes: the larger right lobe and the smaller left lobe.

Lobes1:10–1:34

When viewed from below, the liver has two additional lobes between the the right and left lobe--the posterior caudate lobe and the anterior quadrate lobe.
These two lobes are separated by the porta hepatis, which literally means “the gate to the liver”. Now the porta hepatis contains the hepatic artery, the hepatic portal vein, and the common hepatic duct.

Porta hepatis1:34–2:01

The hepatic artery delivers oxygen-rich arterial blood from the heart to the liver, while the hepatic portal vein delivers nutrient-rich venous blood from the gastrointestinal tract, but also from the spleen, and pancreas.
Lastly, the common hepatic duct drains bile from the liver into the gallbladder. Now let’s take a closer look inside a section of the liver, which shows the functional units of the liver called hepatic lobules.

Hepatic lobules2:01–2:43

Each hepatic lobule looks like a tiny hexagon. At the periphery of the hepatic lobule, there are portal triads which are made up of a branch of the hepatic artery, a branch of the portal vein and one or two small bile ducts.
Now, these branches of the hepatic artery and the portal vein both drain into very porous blood vessels called sinusoids which carry blood towards the center of the lobule and drain into the central vein.
From central veins, the blood flows into the hepatic veins and eventually drain into the inferior vena cava. Now, back in the sinusoids, oxygen and nutrients are able to get through pores in the sinusoids and enter the underlying hepatocytes.

Hepatocytes2:43–4:58

Hepatocytes take in oxygen and nutrients and deposit carbon dioxide into the blood, like all other cells in the body. But in addition, they also pick up and detoxify harmful substances like drugs or alcohol.
Hepatocytes help maintain a normal blood glucose level. When blood glucose levels are high like after eating a meal, hepatocytes convert glucose into a storage molecule called glycogen using a process called glycogenesis.
But, when glucose levels are low, the hepatocytes break down the glycogen back into glucose in a process called glycogenolysis.
In addition to glycogen, hepatocytes also store certain vitamins like A, D, E, K, B12, and some minerals like iron and copper.
The liver also removes the amine group from amino acids, using a process called deamination, so that the amino acids metabolize to help produce ATP.
Hepatocytes also synthesize a variety of important proteins, like albumin and coagulation factors, which get secreted into the blood.
Lastly, these cells also regulate lipid metabolism--they break down fatty acids in order to generate ATP, using a process called beta-oxidation.
Hepatocytes also synthesize two types of lipoproteins: very low-density lipoproteins or VLDL and high-density lipoproteins or HDL.
VLDLs help transport triglycerides, fatty acids, and cholesterol to cells that use them as energy or to adipocytes that store them.
On the other hand, HDLs transport cholesterol from the peripheral cells and tissues back to the liver where they’re broken down to generate energy.
If you’re still not impressed with your liver, consider the fact that you can donate up to 90% of your liver and the remaining 10% can grow it back!
A bit like a starfish that can regrow its arms. Impressive!
Now, speaking of starfish, if we zoom back into the hepatic sinusoid, we’ll notice star-shaped cells called Kupffer cells.

Kupffer cells4:58–5:21

Kupffer cells are modified macrophages, and they’re also called stellate reticuloendothelial cells. They destroy old red and white blood cells, bacteria, and other foreign substances that enter the sinusoids.
Now, the liver is also involved in bile synthesis, which is very important for digestion and absorption of fats and fat-soluble vitamins in the small intestine.

Bile synthesis5:21–6:26

Hepatocytes convert cholesterol into bile salts which along with water and bilirubin make up bile. Bile is secreted into small ducts called bile canaliculi found between adjacent hepatocytes.
From here, the bile flows first into the bile ductules and then into the bile ducts, which are a part of the portal triad.
So, in contrast to blood, which flows from the portal triad toward the central vein, bile flows from the center of the lobule to the portal triad.
The bile ducts then unite to form the larger right and left hepatic ducts, which eventually merge to form the common hepatic duct.
The common hepatic duct then leads to the cystic duct which brings the bile to the gallbladder. The gallbladder is a small pear-shaped hollow organ located beneath the liver, and this is where bile is stored and becomes more concentrated.
Alright, as a quick recap. The liver lies just below your diaphragm in the right upper quadrant of your abdominal cavity and it has a wide range of functions, including metabolism, detoxification, production of proteins important for blood clotting and the bile production.

Review6:26–7:05

The place where the blood vessels enter the liver, while the common hepatic duct leaves it is referred to as the porta hepatis.
Lastly, the main functional unit of the liver is the hepatic lobule, which has a specific hexagonal shape and it consists of four main parts: the portal triad, hepatocytes, hepatic sinusoids and central vein.