The Anatomy and Function of the Human Liver

Human LIver
The liver is a vital organ that performs a number of important functions in the body. It aids in nutrient metabolism and filters the blood of harmful substances. Credit: SEBASTIAN KAULITZKI/Getty Images

The liver is an important vital organ that also happens to be the largest internal organ in the body. Weighing between 3 and 3.5 pounds, the liver is located in the upper right area of the abdominal cavity and is responsible for hundreds of different functions. Some of these functions include nutrient metabolism, detoxification of harmful substances, and protecting the body from germs. The liver has a unique ability to regenerate itself. This ability makes it possible for individuals to donate part of their liver for transplantation.

Liver Anatomy

The liver is a reddish-brown organ that is located below the diaphragm and superior to other abdominal cavity organs such as the stomach, kidneys, gallbladder, and intestines. The most prominent feature of the liver is its larger right lobe and smaller left lobe. These two main lobes are separated by a band of connective tissue. Each liver lobe is internally composed of thousands of smaller units called lobules. Lobules are small liver segments containing arteries, veins, sinusoids, bile ducts, and liver cells.

Liver tissue is composed of two main types of cells. Hepatocytes are the most numerous type of liver cells. These epithelial cells are responsible for most of the functions performed by the liver. Kupffer cells are immune cells that are also found in the liver. They are thought to be a type of macrophage that rids the body of pathogens and old red blood cells.

The liver also contains numerous bile ducts, which drain bile produced by the liver into larger hepatic ducts. These ducts join to form the common hepatic duct. The cystic duct extending from the gallbladder joins the common hepatic duct to form the common bile duct. Bile from the liver and gallbladder drain into the common bile duct and are delivered to the upper portion of the small intestines (duodenum). Bile is a dark greenish or yellow fluid produced by the liver and stored in the gallbladder. It aids in the digestion of fats and helps eliminate toxic wastes.

Liver Function

The liver performs a number of vital functions in the body. A major function of the liver is to process substances in the blood. The liver receives blood from organs including the stomach, small intestines, spleen, pancreas, and gallbladder through the hepatic portal vein. The liver then processes, filters, and detoxifies the blood before sending it back to the heart via the inferior vena cava. The liver has a digestive system, immune system, endocrine system, and exocrine functions. A number of important liver functions are listed below.

1) Fat Digestion

A key function of the liver is the digestion of fats. Bile produced by the liver breaks down fat in the small intestines so that it can be used for energy.

2) Metabolism

The liver metabolizes carbohydrates, proteins, and lipids in the blood that are initially processed during digestion. Hepatocytes store glucose obtained from the break down of carbohydrates in the foods we eat. Excess glucose is removed from the blood and stored as glycogen in the liver. When glucose is needed, the liver breaks down glycogen into glucose and releases the sugar into the blood.

The liver metabolizes amino acids from digested proteins. In the process, toxic ammonia is produced which the liver converts to urea. Urea is transported to the blood and is passed to the kidneys where it is excreted in urine.

The liver processes fats to produce other lipids including phospholipids and cholesterol. These substances are necessary for cell membrane production, digestion, bile acid formation, and hormone production. The liver also metabolizes hemoglobin, chemicals, medications, alcohol and other drugs in the blood.

3) Nutrient Storage

The liver stores nutrients obtained from the blood for use when needed. Some of these substances include glucose, iron, copper, vitamin B12, vitamin A, vitamin D, vitamin K (helps blood to clot), and vitamin B9 (aids in red blood cell synthesis).

4) Synthesis and Secretion

The liver synthesizes and secretes plasma proteins that act as clotting factors and help to maintain proper blood fluid balance. The blood protein fibrinogen produced by the liver is converted to fibrin, a sticky fibrous mesh that traps platelets and other blood cells. Another clotting factor produced by the liver, prothrombin, is needed to convert fibrinogen to fibrin. The liver also produces a number of carrier proteins including albumin, which transports substances such as hormones, fatty acids, calcium, bilirubin, and various drugs. Hormones are also synthesized and secreted by the liver when needed. Liver-synthesized hormones include insulin-like growth factor 1, which aids in early growth and development. Thrombopoietin is a hormone that regulates platelet production in bone marrow.

5)Immune Defense

The K​upffer cells of the liver filter the blood of pathogens such as bacteria, parasites, and fungi. They also rid the body of old blood cells, dead cells, cancer cells, and cellular refuse. Harmful substances and waste products are secreted by the liver into either the bile or the blood. Substances secreted into bile are eliminated from the body through the digestive tract. Substances secreted into the blood are filtered by the kidneys and excreted in urine.