Embryo Project Encyclopedia

Estrogen is the primary sex hormone in women and it functions during the reproductive menstrual cycle. Women have three major types of estrogen: estrone, estradiol, and estriol, which bind to and activate receptors within the body. Researchers discovered the three types of estrogen over a period of seven years, contributing to more detailed descriptions of the menstrual cycle. Each type of estrogen molecule contains a slightly different arrangement or number of atoms that in turn causes some of the estrogens to be more active than others. The different types of estrogen peak and wane throughout women's reproductive cycles, from normal menstruation to pregnancy to the cessation of menstruation (menopause). As scientists better explained the effects of estrogens, they used that information to develop oral contraceptives to control pregnancy, to map the menstrual cycle, and to create hormone therapies to regulate abnormal levels of estrogen.

Frank Rattray Lillie's research on freemartins from 1914 to 1920 in the US led to the theory that hormones partly caused for sex differentiation in mammals. Although sometimes applied to sheep, goats, and pigs, the term freemartin most often refers to a sterile cow that has external female genitalia and internal male gonads and was born with a normal male twin. Lillie theorized that a freemartin is a genetic female whose process of sexual development from an undifferentiated zygote was suppressed or antagonized by her twin's release of male hormones via their shared blood circulation in utero. Despite publications of similar findings by physician Julius Tandler in Vienna, Austria, in 1910 and physician Karl Keller in Wiesensteig, Germany in 1916 prior to Lillie's research, Lillie often receives credit for the hormonal theory of sex differentiation in the freemartin. Lillie's study of freemartins, and the subsequent research by graduate students in Lillie's laboratory at the University of Chicago in Chicago, Illinois, prompted many embryologists to research sex differentiation and hermaphroditism in mammals.

The figure depicts three different molecular structures of estrogen found in mammals’ that differ by the arrangement of bonds and side groups. The molecular structures of the three estrogen molecules differ by the arrangement of chemical bonds and side groups attached to the core steroid structure, cholesterol, which contains three cyclohexane rings and one cyclopentane ring. Compared to the molecular structure of estriol, the molecular structure of estradiol is missing one oxygen-hydrogen or OH group, and estrone lacks the OH group, and one hydrogen molecule that results in a double bonded oxygen atom. These steroid hormones bind to specific cell receptor molecules and induce transcriptional changes in cells. The production of estriol increases during pregnancy, estradiol production increases during stages of the menstrual cycle, and estrone levels increase during menopause. The differing bonds and chemical arrangements enable scientists to determine the different concentrations of the molecules.

In his 1991 article Screening for Congenital Hypothyroidism, Delbert A. Fisher in the US reported on the implementation and impact of mass neonatal screening programs for congenital hypothyroidism (CH) from the early 1970s through 1991. CH is a condition that causes stunted mental and physical development in newborns unless treatment begins within the first three months of the newborn's life. In the early 1970s, regions in Canada and the US had implemented screening programs to diagnose and treat CH as quickly as possible after the infant's birth. By 1991 many other countries had adopted the early screening program, and Fisher estimated that 10 to 12 million newborns per year were tested in the early 1990s. The screening programs, along with physician education and improved screening techniques, such as radioimmunoassay, helped significantly reduce the incidence of abnormal newborn development resulting from untreated congenital hypothyroidism.