Bile Secretion, Functions and Medical Problems areas
Bile secretion is a thick, bitter, yellow, or greenish fluid,
made in the liver and stored in the gall bladder.
Released from the gall bladder into the small intestine,
in response to the presence of food,
it is essential to the digestion of fats.
It is also part of the body’s excretory, or waste disposal system, because it contains the remnants of worn out blood cells.
Bile is Secreated Constantly
Everyday, the liver produces about a litre of bile. Although over 95 percent water, it contains a wide range of chemicals including bile salts, mineral salts, cholesterol, and bile pigments which give the bile its own characteristic color.
It is made continuously and in small quantities by every cell – hepatci cell – in the liver. The biliary system ( or extrahepatic biliary apparatus) is formed by ducts called extrahepatic bile ducts and gall bladder. As it flows from the hepatic cells, it collects in minute, thin channels between groups of liver cells called bile canaliculus,. Few canalaiculus unite to form small ducts, which finally form left and right heptic ducts.
The hepatic ducts join to form common hepatic duct. This duct joins the cystic duct from gall bladder to form common bile duct. Unless bile is needed immediately for digestion, it flows into the gall bladder, which is a storage sack under the liver. After eaching gall bladder the concentration of bile increases.
Composition of Bile Secretion in Liver
Water – 97.5 percent
Bile salt – 1..1 gm percent
Bilirubin – 0.04 gm percent
Cholesterol – 0.1 gm percent
Fatty acids – 0.12 gm percent
Lecithin – 0.04 gm percent
Na +ion – 145 m Eq/l
K +ion – 5 m Eq/l
Ca + ion – 5 m Eq/l
Cl – ion – 100 m Eq/l
HCO3 – 28 m Eq/l
Bile is slightly alkaline in nature, Ph value between 7 and 8.
Bile and Function of Digestion
The bile stays in the gall bladder until given the cue to play its part in the digestive process. As food – but partcularly fatty food – enters the duodenum (the first portion of the intestine) from the stomach, the duodenum makes a hormone called cholecyctokinin.
This harmone travels in the blood stream to the gall bladder and makes it’s walls contract so that bile is squeezed out. The bile then flows down another tube, the common bile duct. The common bile duct unites with pancreatic duct forming common hepatopancreatic duct or ampulla of vater which opens into the duodenum through a narrow gap, the sphincter of Oddi, which lets bile into the small intestine.
Gastrin, secretin, and somatostatin are the other hormones which facilitates this process of the release of bile into the digestive track, along with some inputs coming from the Vagus nerve. The sphincter of Oddi closes up,occasionally so that the bile coming from the liver can be directed into the gall bladder for storage.
How bile works?
Bile’s mineral salts, which include bicarbonate, then neutralize the acidity of partly digested food in the stomach. The bile salts, which are chemcials called sodium glycocholate and sodium taurocholate, break down fats so that digestive chemcials (enzymes) can go to work.
As well as this detergent like action, the bile salts are also believed to act as ferries further down the intestine, enabling digested fats to get through the intestine wall. They are also carriers of vitamins A, D, E, and K, and helps absorb these fat soluble vital minerals.
Functions of Bile
Most of the fucntions of bile are due tothe presence of bile salts in it. Bile salts play a vital role in the processes of digestion and absorption, particularly of fats.
- The bile salts decreases the surface tension of the fat particles to break the fat globules into smaller sizes. This is called the emulsifying or detergent function of bile salts. Bile salts form minute complexes, “micelles,” with the fatty acids and monoglycerides which help in the absorption of fatty acids.
- Bile salts help in activating pancreatic lipase enzymes.
- BIel salts in the duodenum stimulate secretion of pancreatic juice, rich in enzymes, particularly pancreatic lipase.
- Bile salts increase the release of enterokinase from the mucosal cells of duodenum, this enzyme converts trypsinogen into trypsin.
- The alkaline nature of bile helps neutralize acidic chyme (mass of food) in the duodenum.
- Bile acts as an important vehicle for the excretion of numerous drugs, toxins, heavy metals like copper, zinc, and mercury. Bile pigments, enzymes, like alkali phosphatase and pathogenic bacteria like the typhoid bacilli, are excreted in bile.
- Bile exerts a mild laxative effect on the gut by stimulating peristalsis in the small bowel.
- Bile has an antiseptic action and inhibits the growht of certain bacyeria within the gut.
Bile Secretion Recycling
The body is very conservative in it’s use of bile salts. They are not destroyed after use, instead 80 to 90 percent of them are carried back to the liver in the blood where they stimulate in the secretion of more bile and are used again. This cycle of production and re-absorption of bile into the liver is known as enteroheptic circulation. The re-absorption of bile takes place int he lower intestine, and bile normally doesn’t reach the colon.
In case bile reaches the colon it interferes in the absoption of water and salts back into the system which may result in diarrhea.
Bile gets its color from the presence of a pigment called bilirubin. One of the many jobs of th eliver si to break down worn-out red blood cells. As this happens, the red pigment haemoglobin in the cells is chemically split and forms the green pigment biliverdin, whichis quickly converted to the yellow-brown bilirubin.
The greenish timge of bile is given by remnants of unconverted biliverdin. As well as pigmenting the bile, bilirubicolors and partially deodorizes the faeces, and also encourages the intestine to work effectively.
Bile pigment is also responsible in part for the yellow color of urine. In the intestine, bilirubin is attacked by bacteria (minute living creatures) permanently stationed there and converted to a chemical known as uribilinogen, which is carried to the kidneys and released in the urine.
Bile Production – Medical Problems
WHen something is wrong with th eliver or gall bladder, bilirubin tends to accumulate in the blood and the skin and the whites of the eyes look yellow. And because too little bile is reaching the intestines, the faeces mauy be pale and greyish in color.
Evn if the liver’s bile production system is working normally, things can go wrong in the gall bladder. most notorious of gall bladder problems is gall stones. These are hard lumps of a chemical substance called cholesterol, which actually form in the gall bladder.
Bile Secretion Problem’s Treatment
The treatment of bile problems and related diseases depends on their cause. Liver infectins and cirrhosis of the liver are difficult ot treat with drugs and the usual cure is rest, or relaxation, no alcohol, and a nourishing diet.
Surgery is often the only way of treating gall bladder problems, and means removing not just the stones but with them the whole gall bladder. Unless gall stones are so bad that they are a medical emergency, the doctor may first advice a low-fat diet to reduce stress on the system and lower the cholesterol in the blood.
But surgery is often the only permanent answer to gall bladder problems, in whic case the body is quite able to manage without this piece of digestive apparatus. Its removal is an effective operation , and sufferers of chronic gall stones find remarkable relief from previous pai and discomfort.
With the disappearance of the gall bladder the body’s tendency to make stones of choleaterol vanishes, which means their is no danger of gall stones forming in the liver, either.