FUNCTIONAL ANATOMY OF LIVER AND BILIARY SYSTEM

FUNCTIONAL ANATOMY OF LIVER AND BILIARY SYSTEM

Liver is a dual organ having both secretory and excretory functions. It is the largest gland in the body, weighing about 1.5 kg in man. It is located in the upper and right side of the abdominal cavity, immediately beneath diaphragm.

LIVER

Hepatic Lobes

Liver is made up of many lobes called hepatic lobes. Each lobe consists of many lobules called

hepatic lobules.

Hepatic Lobules

Hepatic lobule is the structural and functional unit of liver. There are about 50,000 to 100,000 lobules in the liver. The lobule is a honeycomb-like structure and it is made up of liver cells called hepatocytes.

Hepatocytes and Hepatic Plates

Hepatocytes are arranged in columns, which form the hepatic plates. Each plate is made up of two columns of cells. In between the two columns of each plate lies a bile canaliculus .

In between the neighboring plates, a blood space called sinusoid is present. Sinusoid is lined by the

endothelial cells. In between the endothelial cells some special macrophages called Kupffer cells are present.

Portal Triads

Each lobule is surrounded by many portal triads. Each portal triad consists of three vessels:

1. A branch of hepatic artery

2. A branch of portal vein

3. A tributary of bile duct.

Branches of hepatic artery and portal vein open into the sinusoid. Sinusoid opens into the central vein.

Central vein empties into hepatic vein. Bile is secreted by hepatic cells and emptied into bile canaliculus. From canaliculus, the bile enters the tributary of bile duct. Tributaries of bile duct from canaliculi of neighboring lobules unite to form small bile ducts. These small bile ducts join together and finally

form left and right hepatic ducts, which emerge out of liver.

BILIARY SYSTEM

Biliary system or extrahepatic biliary apparatus is formed by gallbladder and extrahepatic bile ducts (bile

ducts outside the liver). Right and left hepatic bile ducts which come out of liver join to form common hepatic duct. It unites with the cystic duct from gallbladder to form common bile duct. All these ducts have similar structures. Common bile duct unites with pancreatic duct to form the common hepatopancreatic duct or ampulla of Vater, which opens into the duodenum. There is a sphincter called sphincter of Oddi at the lower part of common bile duct, before it joins the pancreatic duct. It is formed by smooth muscle fibers of common bile duct. It is normally kept closed; so the bile secreted from liver enters gallbladder where it is stored. Upon appropriate stimulation, the sphincter opens and allows flow of bile from gallbladder into the intestine.

 BLOOD SUPPLY TO LIVER

Liver receives maximum blood supply of about 1,500 mL/minute. It receives blood from two sources, namely the hepatic artery and portal vein.

HEPATIC ARTERY

Hepatic artery arises directly from aorta and supplies oxygenated blood to liver.

PORTAL VEIN

Portal vein is formed by superior mesenteric vein and splenic vein. It brings deoxygenated blood from stomach, intestine, spleen and pancreas. Portal blood is rich in monosaccharides and amino acids. It also contains bile salts, bilirubin, urobilinogen and GI hormones. However, the oxygen content is less in portal blood. Flow of blood from intestine to liver through portal vein is known as enterohepatic circulation.

The blood from hepatic artery mixes with blood from

portal vein in hepatic sinusoids. Hepatic cells obtain

oxygen and nutrients from the sinusoid.

HEPATIC VEIN

Substances synthesized by hepatic cells, waste products and carbon dioxide are discharged into sinusoids. Sinusoids drain them into central vein of the lobule. Central veins from many lobules unite to form bigger veins, which ultimately form hepatic veins (right and left) which open into inferior vena cava.

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