Estrogens (estrone, estriol, and estradiol) are a class of steroidal hormones
produced by developing ovarian follicles. These hormones induce various cyclic events
in the uterine endothelium and vaginal epithelium and make the female body
competent for conception and ultimately for motherly care. While estrogen is primarily
produced by ovaries from cholesterol, the non-reproductive tissues including the brain,
liver, and heart also produce a considerable amount of it. Apart from its important role
in controlling sexual behavior and reproductive function, estrogen also functions in the
regulation of various physiological functions including reproduction, skin physiology,
cardiovascular health, skeletal homeostasis, bone integrity, electrolyte balance,
cognition, and behavior. These biological functions are regulated by diffusion through
the plasma membrane in vitro signaling through specific binding to nuclear receptors
such as estrogen receptors (ERα and ERβ) or binding to cell membrane receptors such
as GPR30 and ER-X. The signaling mechanism can be genomic (change in gene
expression) or non-genomic (activation of various signaling cascades). Disruption in
estrogen functioning has a pivotal role in the pathogenesis of many diseases such as
osteoporosis, insulin resistance, neurodegenerative disease, obesity, and endometriosis.
Also, dysregulation in the levels of estrogen has been linked to the development of
many cancers such as breast cancer, etc. This chapter aims to summarize the complete
insight of estrogen by providing a clear understanding of its synthesis, receptor
binding, signaling, regulation of physiological functions, and role in various diseases.
Keywords: Breast cancer, Endometriosis, Estradiol, Estrogen, Estrogen receptors, Estrogen signaling, Estrogen synthesis, Lymphangioleiomyomatosis, Prostate cancer, Sex hormones, Steroidal hormones.
