Which of the following hormones is synthesized from cholesterol?

Estrogen is synthesized from cholesterol as it belongs to a class of hormones known as steroid hormones. Steroid hormones are derived from cholesterol through a series of enzymatic reactions in the body. This process involves the conversion of cholesterol into pregnenolone, which is then converted into various steroid hormones, including estrogens. The synthesis of estrogen primarily occurs in the ovaries in females and in smaller amounts in other tissues.

In contrast, secretin and gastrin are peptide hormones that are made up of amino acids and are not synthesized from cholesterol. Secretin is produced in the small intestine and plays a role in regulating the pH of the small intestine by stimulating the pancreas to release bicarbonate. Gastrin is produced in the stomach and stimulates the secretion of gastric acid, both of which highlight its role in digestion rather than cholesterol-based synthesis.

Dopamine, on the other hand, is a neurotransmitter synthesized from the amino acid tyrosine, which is also not related to cholesterol synthesis. This further distinguishes it from estrogen and reinforces the understanding that estrogen is indeed the hormone derived from cholesterol.