The Liver

The liver has anatomically separate lobes and eight functionally independent segments based on blood supply and natural anatomic separations. These segments are used for surgical classification because they allow for hepatic resection along segmental planes, thus preserving function and tissue integrity. The surgical classification system is called Couinad's classification.

The four major lobes of the liver are divided by fissures and include:

i. the right anatomical lobe (larger), which has two smaller lobes located at its posterior-inferior surface

ii. the left anatomical lobe

iii. the smaller, inferior lobes are referred to as the caudate lobe and

iv. quadrate lobe.

The major division of the liver (left and right lobes) is the falciform ligament .

The human liver is the largest gland/organ in the body and weighs approximately 1500-1600 gm in adults (~2% of total body mass). It is known for having a large functional reserve and is responsible for an extensive number of complex functions in humans including:

1. Blood reservoir / filter
2. Regulation of blood coagulation
3. Glucose regulation
4. Erythrocyte breakdown and bilirubin excretion
5. Intermediary metabolism regulation (bile production)
6. Protein synthesis (albumin, coagulation factors, etc.)
7. Host defense
8. Pharmacokinetics / Drug metabolism
9. Hormone metabolism


Functional and Microanatomy

Hepatic tissue is made of 50,000-100,000 discrete, hexagonally shaped anatomic units called lobules . Lobules contain plates of hepatocytes arranged cylindrically around a centrilobular vein .

The portal tracts (or “triads”) include 4-5 tracks surrounding each lobule that contain
- hepatic arterioles which carry oxygenated blood from hepatic artery,
- the portal venules which carry partially deoxygenated blood from the portal vein,
- bile caniliculi that join to form bile ducts.

The hepatic sinusoids / ducts act as capillaries between the central vein and portal tracts and contain endothelial cells and macrophages ( Kupffer cells ).
Kupffer cells are responsible for phagocytosis of calonic bacteria, endotoxins, cellular debris, viruses, proteins, and particulate matter, antigen processing, and the release of proteins, enzymes, cytokines, and chemical mediators.
The Space of Disse lies between the hepatic sinusoids and the hepatocytes.
Additionally, and extensive system of lymphatic ducts and nerves is located through hepatic tissue.

The functional cellular anatomy of the liver can be divided into three zones:

- Zone 1 – closest to blood vessels, well oxygenated, least susceptible to injury
- Zone 2 – adequately oxygenated
- Zone 3 – closest to centrilobular vessels, least oxygenated, most susceptible to injury

Blood Supply


Normal hepatic blood flow is ~1500 cc/min in adults (25-30% of total CO) and normal hepatic blood volume is ~450 cc. The liver has the unique ability to augment circulating blood volume by up to 300 cc during low volume states such as dehydration or hemorrhage. Additionally, it can also hold up to 1 L of blood at the expense of hepatic congestion. The blood supply is a dual system also known as a portal system. The two major vessels that provide blood to the liver are the hepatic artery and portal vein .

The hepatic artery arises from the celiac artery (from aorta) and comprises 25-30% of total blood flow to the liver. It supplies 45-50% of oxygen requirement and flow is dependant on metabolic demand (autoregulated). The normal saO2 of blood in the hepatic artery is 98%. The portal vein is formed at the anastamosis of the superior mesenteric and splenic veins and comprises 70-75% of total blood flow to the liver. It supplies 50-55% of oxygen requirement and the normal saO2 of portal venous blood is 85%. This blood is partially deoxygenated prior to entering the liver in the stomach, spleen, intestines, and pancreatic vessels. Normal hepatic venous pressure is 7-10 mmHg and flow is dependent on blood flow to the GI tract and spleen. The blood from these organs is laden with nutrients from GI tract.

The intrahepatic circulation of blood is as follows:

The hepatic artery and portal vein split into left and right branches ---> enter liver and diminish in size throughout the hepatic tissue ---> become terminal hepatic arterioles and portal venules ---> drain directly into hepatic sinusoids (see above) ---> terminal hepatic venules into a central vein ---> sublobular veins which get larger and ultimately form ---> three major hepatic veins (right, middle, and left) ---> inferior vena cava.

Duct System

The duct system or hepatobiliary system is composed of the following:

i. Bile ducts from hepatic lobules combine to form

ii. the left and right hepatic ducts which connect to form the hepatic duct which together with

iii. the cystic duct from the gallbladder form

iv. the common bile duct which then meets with

v. the pancreatic duct and empties into the duodenum of the small intestine under the control of the Sphincter of Oddi:

Contract: bile is blocked from entering the duodenum

Relax: allows bile to enter the duodenum