Final answer:
Gallstones (cholelithiasis) are solid particles formed in the gallbladder due to an excessive accumulation of cholesterol. They tend to increase with age and are more common in specific populations such as premenopausal women, pregnant or breastfeeding women, and older adults.
Step-by-step explanation:
Gallstones (cholelithiasis) are solid particles formed in the gallbladder when a large amount of cholesterol accumulates and precipitates. They are almost 100% cholesterol with small amounts of calcium salts, glycerophospholipids, and fatty acids. Gallstones tend to increase with age and are more common in specific populations such as premenopausal women who may need extra calcium and iron, women who are pregnant or breastfeeding, and older adults.