Your liver makes a substance called bile and sends it to your gallbladder, where it is stored and concentrated. The gallbladder releases bile whenever you need to break up fats. If the bile has too much cholesterol, that liquid bile will become hard and form a cholesterol gallstone. According to the National Digestive Diseases Information Clearinghouse, approximately 10 percent of adults have gallstones and 80 percent of them are cholesterol gallstones. But if your bile has too much of a substance called bilirubin, it forms another type of gallstone: a black pigmented gallstone. Certain diseases and infections cause black pigmented gallstones.
Sickle Cell Anemia
Hemoglobin is a protein in your red blood cells that is needed for the cells to carry oxygen. In sickle cell anemia, instead of the amino acid glutamine being in its proper place in the hemoglobin molecule, it has been substituted by the amino acid valine. This change causes the red blood cells to form a sickle shape. Now fragile and destroyed in high numbers, this destruction releases high levels of hemoglobin. Hemoglobin is normally converted to bilirubin, a component of bile. But if there is too much bilirubin, the bilirubin binds to calcium, hardens and forms black pigmented gallstones.
Hereditary Spherocytosis
In this disease, the membrane of red blood cells does not have enough of a protein called spectrin. This protein has a major responsibility for the flexibility, strength and shape of the red blood cells. A decreased amount results in cells that are spherical in shape. When they pass through the spleen, they are held there and destroyed. Similar to sickle cell anemia, their destruction causes the release of high amounts of hemoglobin and, therefore, high amounts of bilirubin will be produced. The bilirubin will bind to calcium, harden and form black gallstones.
Alcoholic Liver Disease
There are three forms of a diseased alcoholic liver. One form is called hepatic steatosis. This term is used to describe a "fatty liver," where the damage caused by alcohol results in liver cells that are filled with fat. Another form is alcoholic hepatitis, where the liver is inflamed. The third form is alcoholic cirrhosis, where the liver damage is irreversible. When hemoglobin is converted to bilirubin, the bilirubin binds to a protein called albumin and is sent to the liver. As explained by Kim Barrett, PhD in "Gastrointestinal Physiology," when bilirubin reaches the liver, it is changed and becomes part of bile. But if the liver is so damaged that bilirubin cannot be changed, the wrong type is made part of bile. There is no albumin protein for that form to bind to, so it binds to calcium. This hardens and forms black gallstones.
Biliary Infections
This is the name given to bacterial infections that take place in the biliary tract, the path where bile flows. Bacteria have an enzyme that can change the form of bilirubin that is normally found in bile, back to the form that it had when it first came to the liver. In other words, bacteria change bilirubin back to the form that has to bind to albumin. As in the case of alcoholic liver disease, bacteria cause the wrong form of bilirubin to become part of bile. Once again, there is no albumin in bile for the bilirubin to bind to, so it binds to calcium, hardens and forms black gallstones.
References
- "Gastrointestinal Physiology"; Kim Barrett, PhD; 2006
- National Digestive Diseases Information Clearinghouse: Gallstones
- "Robbins Pathologic Basis of Disease"; Ramzi Cotran, M.D., Vinay Kumar, M.D., Stanley Robbins, M.D.; 1994
