Estrogen is classified as a steroid hormone, which is a type of lipid. More specifically, it belongs to a group of lipids known as steroids, which are derived from cholesterol. Steroids are characterized by a structure of four interconnected carbon rings. In the case of estrogen, this structure is modified to include various functional groups that give it its biological activity.
Estrogen plays a crucial role in various physiological processes, including the regulation of the menstrual cycle, maintenance of pregnancy, and development of secondary sexual characteristics. Being a lipid allows estrogen to easily pass through cell membranes and bind to specific receptors inside cells, facilitating its effects on gene expression and cell function.