Bile salts are formed in the hepatic cells from cholesterol
in the blood plasma. In the process of secreting the
bile salts, about 1 to 2 grams of cholesterol are removed
from the blood plasma and secreted into the bile each
day.

in the bladder in progressively greater concentrations.
Then the cholesterol begins to precipitate, first forming
many small crystals of cholesterol on the surface of
the inflamed mucosa, but then progressing to large
gallstones.
Cholesterol is almost completely insoluble in pure
water, but the bile salts and lecithin in bile combine
physically with the cholesterol to form ultramicroscopic
micelles in the form of a colloidal solution, as explained
in more detail in Chapter 65. When the bile becomes
concentrated in the gallbladder, the bile salts and
lecithin become concentrated along with the cholesterol,
which keeps the cholesterol in solution.

Under abnormal conditions, the cholesterol may precipitate
in the gallbladder, resulting in the formation of
cholesterol gallstones. The amount of cholesterol in the bile is determined partly by the quantity of fat that the person eats, because liver cells synthesize cholesterol as one of the products of fat metabolism in the body. For this reason, people on a
high-fat diet over a period of years are prone to the
development of gallstones.

Inflammation of the gallbladder epithelium, often
resulting from low-grade chronic infection, may also
change the absorptive characteristics of the gallbladder
mucosa, sometimes allowing excessive absorption of
water and bile salts but leaving behind the cholesterol
in the bladder in progressively greater concentrations.
Then the cholesterol begins to precipitate, first forming
many small crystals of cholesterol on the surface of
the inflamed mucosa, but then progressing to large
gallstones.