Estrogen receptors are proteins found in various tissues throughout the body that bind to the hormone estrogen. They play a crucial role in mediating the effects of estrogen, which is important for reproductive health, bone density, and cardiovascular function. There are two main types of estrogen receptors: ERα and ERβ, each with different functions and tissue distributions. When estrogen binds to these receptors, it triggers a series of cellular responses that influence gene expression and cellular activity. This process is vital for regulating various physiological processes, including the menstrual cycle, pregnancy, and the development of secondary sexual characteristics.