Introduction
Bile (or bile fluid) is a fluid produced by the liver cells and is important for the digestion and excretion of waste products. Contrary to the widespread misconception that bile is produced in the gallbladder, this fluid is produced in the liver. Here, there are special cells, the so-called hepatocytes, which are responsible for the production of bile.
Between every two liver cells there are small channels into which the fluid is released. In addition, other substances, including
- Bile salts
- Cholesterol
- Bilirubin and
- Hormones are secreted into it.
These tubules join together to form larger and larger channels (= bile ducts) and ultimately only one duct, the Ductus hepaticus communis, leads the bile out of the liver. At this point in time, the bile is usually rather thin and yellowish, it is called “liver bile”.
From this common hepatic duct, a cystic duct (Ductus cysticus) branches off to the gallbladder, through which the bile flows into the gallbladder in case of backflow. If there is no backwater, the fluid passes through the following section, the choledochal duct, to the duodenum, where the bile duct finally opens into the large papilla (papilla duodeni major) together with the pancreatic duct. The gallbladder thus practically serves as a reservoir for the bile. There, water is removed from the fluid, causing it to thicken to almost a tenth of its original volume, making it more viscous and its coloration now tends towards greenish (“bladder bile”).
Production
Every day, humans produce about 700ml of bile, which is initially stored in the gallbladder, except for a small percentage that is conducted directly into the intestine. When food is consumed and fats reach the small intestine, this stimulates the release of various hormones, including the hormone cholecystokinin CCK. This hormone stimulates the smooth muscles embedded in the wall of the gallbladder and thus leads to a contraction of the gallbladder.
This causes the contents of the gallbladder (i.e. the bile) to be transported outwards and enter the duodenum. An activity of the parasympathetic part of the autonomic nervous system, which is mediated here via the vagus nerve, has the same effect on the gallbladder. The bile consists mainly of water (about 85%).
Other components of the bile are, in certain proportions, the
- Bile acids
- Electrolytes
- Glycoproteins (Muzine)
- Lipids
- Cholesterol and
- Excretion products of the body, such as drugs or hormones
The dye bilirubin is also eliminated via the bile, which is responsible for its greenish to brown color. The bile fulfils two important functions in the body. On the one hand, it serves the digestion of fats.
The bile acids form so-called micelles in the duodenum with the non-water-soluble components of food (i.e. fats, some vitamins and cholesterol). This enables these substances to be absorbed from the intestine into the blood. The bile acids are removed from the lumen in the rear section of the small intestine and return to the liver via the blood, where they are again available for fat digestion.
This saves the body from the costly new synthesis of the bile acids. This process is called enterohepatic circulation. The second function of bile is to excrete metabolic waste products or breakdown products of the body that have previously been made water-soluble in the liver.
If the composition of the bile is incorrect, problems can occur. For example, if there is either too much cholesterol or too much bilirubin in the bile in relation to the water content, gallstones (correspondingly either cholesterol stones, the more common form, or bilirubin stones) can form. Symptomatic gallstones become noticeable by pressure pain in the (right) upper abdomen, cramp-like pain (colic) and possibly jaundice (icterus).
Jaundice is caused by the fact that the breakdown product of the red blood pigment haemoglobin, bilirubin, can no longer be excreted and therefore accumulates in the blood. Consequently, the stool loses its color and becomes grayish-white.Apart from gallstones, blockage of the bile ducts (also known as cholestasis) can have many other causes. These include tumors of the bile duct or bladder, pancreas and duodenum. In addition to the above-mentioned icterus, these diseases also cause a disturbed fat digestion, which means that high-fat food is not tolerated as well and occasionally fats can be found in the stool (steatorrhea).
