What is the gallbladder?
The gallbladder is a sack like organ attached to, and tucked under, the liver. It has an important function in the digestive system. Digestion is the process of making nutrients and energy producing substances available to body tissues and cells.
The role of the gallbladder is to collect and store bile that the liver has produced and discharge it into the small intestine after a fatty meal. When functioning correctly a person is not aware of their gallbladder. However, if something does go wrong it can be very painful. One of the most common and painful complications is gallstones.
Why does the gallbladder produce bile?
Bile is a thick, bitter, yellowish or greenish fluid made in the liver and stored in the gallbladder. The function of bile is to neutralise the acidity of partially digested food in the duodenum, which is the first part of the small intestine. Bile is released from the gallbladder into the small intestine in response to the presence of food and is essential to the digestion of fats.
Food leaves the stomach as a thickish, acidic liquid called chyme and enters the duodenum. The duodenum makes and releases large quantities of mucus, which protects it from damage by acid and other enzymes in the chyme. The duodenum also receives pancreatic juices from the pancreas and considerable quantities of bile, which is made in the liver and stored in the gallbladder.
The liver produces approximately 1 litre of bile daily. Although over 95 per cent water, bile contains a wide range of chemicals including bile salts, mineral salts, cholesterol and bile pigments which give it a characteristic greenish colour.
How does bile move from the liver to the gallbladder to the duodenum?
Bile is made continuously by every cell in the liver. It flows from these cells and collects in minute channels between groups of liver cells called bile caniculi, which empty into bile ducts. From the bile ducts, bile drains into hepatic ducts, or exit tubes. Unless bile is needed immediately for digestion, it flows into the gallbladder.
Bile stays in the gall bladder until required for digestion. As food, especially fatty food, leaves the stomach and enters the duodenum a hormone called cholecystokinin is secreted. This hormone travels in the bloodstream to the gall bladder and makes its walls contract so that the stored bile is squeezed out. The bile flows down to the common bile duct, which is also a tube, and through a narrow gap which allows the bile to pass into the small intestine.
Why is bile important?
Bile’s mineral salts, including bicarbonate, neutralise the acidity of the partially digested food. The role of the bile salts is to break down fats so the digestive enzymes can go to work. Bile salts also act as transporters further down the intestine firstly, enabling digested fats to transfer through the intestine wall and secondly, as carriers of vitamins A, D E and K.
The body is very conservative in its use of bile salts and recycles them as part of digestion. They are not destroyed after use but instead approximately 80-90 per cent are transported in blood back to the liver where they once again stimulate the secretion of more bile.
Bile contains the pigment bilirubin; a by-product of liver function. One of the liver’s many functions is to breakdown worn out red blood cells. As this happens, the red pigment haemoglobin splits and forms the pigment biliverdin. Biliverdin quickly converts to bilirubin, which is yellowish brown, and is the reason for bile’s colour. Bilirubin also encourages the intestine to work effectively, deodorises the faeces and contributes to the yellow colour of urine.
When the liver or gallbladder is not functioning correctly bilirubin accumulates in the blood and results in jaundice with the skin and whites of eyes looking yellow. Also, because not enough bile is reaching the intestine, faeces may be pale and greyish. Therefore jaundice and pale, greyish faeces are two symptoms that gallbladder function is not as it should be.
What are gallstones?
Even when bile production is normal other things can go wrong with the gallbladder. The most common of these is gallstones. Gallstones are small hard lumps of cholesterol, produced in the body by the breakdown of fats, which form in the gallbladder.
There are three kinds of gallstones. The first, mixed stones are the most common. They contain a mix of the bile pigment biliverdin and cholesterol. Mixed gallstones develop in clutches, up to 12 at a time. Secondly, cholesterol stones, as their name suggests, comprise mostly of cholesterol, grow up to 1.25cm in diameter and are large enough to block the common bile duct. The third, pigment stones are usually very small and occur in large numbers. They are made mostly of biliverdin, the green bile pigment. Pigment stones tend to form from illnesses affecting blood composition.
Gallstones are not automatically painful. Many people have gallbladder stones without being aware of them. However if a gallstone blocks the bile duct severe and repeated pain is probable. Depending on the severity and frequency of attacks, gallstones can be controlled with a healthy diet but may need surgery.