Bilirubin or golden yellow pigment, and Biliverdin the green coloured pigment are solely responsible for the characteristic colour of bile. Hemoglobin from the old and dead red blood cells undergoes a destructive metabolism or catabolism, and gives rise to the billirubin and biliverdin pigments. Cholesterol, traces of fats and fatty acids and lecithin are the prime lipid materials which are included in bile. Bile also contains some proteins like mucin, and traces of globulin, albumin etc.
Bile also contains the enzyme alkaline phosphatase which has no function in digestion.The canalicular hepatocytemembrane and the epithelial cells lining the bile duct has an expensive concentration of Alkaline phosphatase. When considerable amounts of this enzyme is found in the blood, it usually indicates that there is some problem with the function of the kidneys, liver or the bones. Liver cirrhosis treatment cost in India is low and it includes the blood test for alkaline phosphatase. In addition to the excretorymatters, for example, the bile pigments, cholesterol etc. some drugs may also be excreted through the bile. Hence bile is appropriately considered as a secretary as well as an excretory product of the liver.
Bile can be categorised into two different types depending on the flow:
- Black Bile: If the flow of bile from gallbladder to intestine is obstructed due to an obstruction in the bile duct, that is distal to the joining of the cystic duct with the common hepatic duct. The flow of bile from liver to gallbladder is maintained for some time due to absorption of water from the gallbladder.As a result of this, the gallbladder is ultimatelyfilled up with a thick and greenish fluid known as the black bile. The former is therefore an extensively concentrated form of the bile.
- White Bile: if there is an obstruction in the common hepatic duct proximal to the joining of cystic duct within the bile cannot flow from liver to gallbladder in such a condition of white fluid containing gluten is accumulated in gallbladder and bile duct this is known as the white the former is not well at all because it does not originate in the liver.
Functions Of Bile
- Bile does not contain any digestive enzyme yet it helps in the digestion of fat indirectly, by promoting the action of pancreatic and intestinal lipases due to the presence of bile salts in it.
- The former may stimulate the action of lipases in two ways.They may either activate the lipases or they may emulsify the fat into small droplets, so as to facilitate the action of lipases.
- Bile is essential for the absorption of fat.This is attributed to the hydrotropic action of bile salts.Thishighlights the ability of bile salts to make water insoluble products of fat digestion. For example, fatty acids, diglycerides, monoglycerides etc. readily soluble in water and diffusible so that they can be easily absorbed.
- Bile salts also help in the absorption of fat soluble vitamins,irons, carotene etc.
Bile actually helps in lipid digestion. It also helps in the digestion of fats in the duodenum.