Gallstones: what are they?

gallbladder and biliary tract

Gallstones are stone-like deposits that form in the gallbladder, a small pear-shaped organ located under the liver. The gallbladder is responsible for the storage of bile, a greenish-brown fluid used in the digestive process to digest fats. Bile is made in the liver.

How do gallstones form?

Gallstones develop when crystals form in bile, the liquid stored in the gallbladder. Over time, the crystals can grow into hard, stone-like lumps.

Bile consists of a number of components, including cholesterol, bile salts, bilirubin and water. If your gallbladder fails to empty properly, or if the cholesterol, bile salts or bilirubin become too concentrated, you may develop gallstones.

Types of gallstones

Gallstones may be tiny, like a pinhead, or as large as a golf ball, and may vary in number from one to several hundred. Lots of small crystals can form so-called 'biliary sludge'.

There are 2 main types:

  • cholesterol stones; and
  • pigment stones.

Cholesterol stones are the more common type of gallstones. They are generally a yellowy-green colour, and can occur if your liver produces too much cholesterol.

Pigment stones occur less frequently. They are small and dark brown or black in colour, and consist of bilirubin salts. Pigment stones tend to occur in people with cirrhosis of the liver, biliary tract infections or certain blood disorders.

How common are gallstones?

About 10 per cent of the general Australian population (and 15 per cent of people older than 50 years) have gallstones, although they often do not show any symptoms.

Risk factors

There are several groups who are more at risk of developing gallstones than others. Risk factors include:

  • being female;
  • age older than 40 years;
  • being overweight or obese;
  • rapid weight loss;
  • a diet that is high in calories, fat, cholesterol or refined carbohydrates, and low in fibre;
  • excess oestrogen from taking contraceptive pills or hormone replacement therapy, or being pregnant;
  • family history of gallstones;
  • diabetes;
  • liver cirrhosis; and
  • taking certain medicines, including some cholesterol-lowering medicines.

References

1. NHS Choices. Gallstones (updated 18 Nov 2013). http://www.nhs.uk/conditions/gallstones/pages/introduction.aspx (accessed Aug 2015).
2. MayoClinic. Gallstones (updated 25 Jul 2013). http://www.mayoclinic.org/diseases-conditions/gallstones/basics/symptoms/con-20020461 (accessed Aug 2015).
3. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Gallstones (updated 27 Nov 2013). http://www.niddk.nih.gov/health-information/health-topics/digestive-diseases/gallstones/Pages/facts.aspx (accessed Aug 2015).
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