"Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important
class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol. Cholesterol is vital to cellular function, and a precursor to fat-soluble vitamins and steroid hormones."
"Sterols of plants are called phytosterols and sterols of animals are called zoosterols. Important zoosterols are cholesterol; notable phytosterols include campesterol, sitosterol, and stigmasterol.Ergosterol is a sterol present in the cell membrane of fungi, where it serves a role similar to cholesterol in animal cells."
"Sterols and related compounds play essential roles in the physiology of eukaryotic organisms. For example, cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane's fluidity and serves as secondary messenger in developmental signaling. In humans and other animals, corticosteroids, such as cortisol act as signaling compounds in cellular communication and general metabolism."