What Are Gallstones

Gallstones are lumps of solid material that form in the gallbladder. They usually look like small stones or gravel, but can be as small as sand or as large as pebbles, sometimes filling the gallbladder. They may take years to grow and there may be one or several.

Gallstones are formed from the chemicals in bile and may be:

  • Pure cholesterol stones which are yellow – these are the most common type of stone and are made up of cholesterol, which is a type of fat
  • Pure pigment stones  which are black – these consist of calcium and bilirubin (a pigment from broken down red blood cells) which have solidified
  • Mixed stones – these are a combination of cholesterol and pigment stones

Gallstones are formed when the different elements which make up your bile become imbalanced. Cholesterol stones form when cholesterol levels in your bile are too high, this causes the cholesterol in your bile to crystalize and come out of solution.

Gallstones run in families and are much more common in women than men. About one in four women and one in eight men develop gallstones at some stage in their life. They are more common during women's fertile years and during pregnancy. This is because cholesterol is a component of oestrogen, and at these times fluctuating levels of oestrogen need to be broken down to cholesterol and excreted in bile.

Pigment stones may form when the amount of bilirubin in bile is excessive. This can occur in conditions such as sickle cell disease and thalassaemia.

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