A bile canaliculus is an extremely narrow passageway within the liver. Some people describe a bile canaliculus as an ultra-thin tube, but this not entirely accurate, as bile canaliculi are actually grooves formed by variations in the faces of liver cells. Its primary function is to collect and transport the bile produced by hepatocytes, or liver cells. There are thousands of canaliculi within the liver.
Under normal circumstances, a bile canaliculus generally is about one micrometer, or one millionth of a meter, in diameter. By comparison, a typical red blood cell has a diameter of around six to eight micrometers. A single bile canaliculus thus cannot collect a large amount of bile, but because there are so many canaliculi within the liver, the liver is able to get rid of the roughly half a liter, or just over two cups, of bile produced on a daily basis.
Bile canaliculi are the first part of the bile transport system. Eventually, the canaliculi join to larger bile ductules. The ductules then join to form the common hepatic duct. The canaliculi are similar in transport function to the capillaries of the circulatory system, which are connected to larger veins and arteries. For this reason, another name for a bile canaliculi is bile capillary.
Capillaries that transport bile are fairly stable in a healthy liver, as hepatocytes usually don't divide except to repair damage. When there are problems with the liver cells and liver function, however, the structure of the canaliculi may change. The amount of bile a bile canaliculus transports also can shift, as an unhealthy liver may not produce as much bile. Under certain circumstances, bile canaliculi also can become blocked.
Bile serves multiple functions in the body, one of which is to aid digestion. It also helps remove waste such as bilirubin. If liver function is impaired and bile canaliculi do not transport enough bile, people may experience symptoms of nutritional deficiency. They also may experience other toxin-related issues such as jaundice, one of the leading and most outwardly-visible signs of liver distress.
Physicians are able to study bile canaliculi primarily through the examination of liver tissue under a microscope. Staining liver tissue with various dyes helps make the bile capillaries more visible. The staining procedure is of great use to doctors and their patients because changes in normal capillary structure can confirm the presence of liver disease. Once liver disease is diagnosed, the doctor and the patient can discuss and proceed with whatever treatment options are available given the specific liver illness.