Embryo Project Encyclopedia Articles

The sex of a reptile embryo partly results from the production of sex hormones during development, and one process to produce those hormones depends on the temperature of the embryo's environment. The production of sex hormones can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination, also called genetic or chromosomal sex determination, an organism's genes determine which hormones are produced. Non-genetic sex determination occurs when the sex of an organism can be altered during a sensitive period of development due to external factors such as temperature, humidity, or social interactions. Temperature-dependent sex determination (TSD), where the temperature of the embryo's environment influences its sex development, is a widespread non-genetic process of sex determination among vertebrates, including reptiles. All crocodilians, most turtles, many fish, and some lizards exhibit TSD.

In 1949, Priscilla White published Pregnancy Complicating Diabetes, which described the results and implications of a fifteen-year study about pregnant diabetic women. Published in the American Journal of Medicine, the article details possible causes of and ways to prevent the high fetal mortality rate associated with pregnant diabetic women. Diabetes is a disease in which the body's ability to produce or respond to the hormone insulin is impaired, and it can be particularly dangerous during pregnancies. In her article, White reported that prematurely delivering infants for diabetic pregnant women reduces infant and maternal mortality rates. Pregnancy Complicating Diabetes helped make premature delivery of infants the standard of care for diabetic pregnant women, and it has contributed to the increased survival rate of infants born from diabetic mothers from less than fifty percent in the 1940s to over ninety percent in 2017.

In 1996, the US Congress mandated that the US Environmental Protection Agency (EPA) create and regulate the Endocrine Disruptor Screening Program. The program tests industrial and agricultural chemicals for hormonal impacts in humans and in wildlife that may disrupt organisms' endocrine systems. The endocrine system regulates the release of small amounts of chemical substances called hormones to keep the body functioning normally. Some chemicals can impede the endocrine system's function by mimicking or blocking hormone reception, which can disrupt processes of development and reproduction and harm organisms. As of 2017, the Endocrine Disruptor Screening Program is the largest US program to identify and regulate chemicals that affect the normal production of sex hormones like estrogen and androgen, which can have long-term effects on development and reproduction.

Edward Charles Dodds researched the function and effects of natural and artificial hormones on the endocrine system in England during the twentieth century. Though he first worked with hormones such as insulin, Dodds focused on the effects of estrogen in the body and how to replicate those effects with artificial substances. In 1938, along with chemist Robert Robinson, Dodds synthesized the first synthetic estrogen called diethylstilbestrol. Despite the wide use of diethylstilbestrol to treat a variety of hormonal problems like miscarriages during pregnancy and menopause, Dodds argued against the use of synthetic substances in the human body due to their unknown effects. Just before Dodds's death, his hypotheses were confirmed when researchers showed that people exposed to diethylstilbestrol often developed cancer. Dodds was one of the first researchers to investigate the endocrine or hormone system in humans, and his research led to the creation of other synthetic hormones used in contraceptive pills and hormone replacements.

In 1948, Olive Watkins Smith published 'Diethylstilbestrol in the Prevention and Treatment of Complications of Pregnancy' in the American Journal of Obstetrics and Gynecology. In 632 women treated with diethylstilbestrol, Smith demonstrated that the drug stimulated the production of progesterone, a hormone that regulates the uterine condition during pregnancy. On the basis of her article, and several follow up articles authored by Smith and her husband, George Van Siclen Smith, physicians around the world began prescribing DES to women at risk for pregnancy complications like miscarriage and premature delivery. However, in 1953, researchers at found that DES did not prevent pregnancy complications. In 1970, researchers linked fetal exposure to DES to rare and severe cancers later in life. Researchers labeled DES as an endocrine disruptor, a substance that disrupts the hormone system of the body across multiple generations.

Sindell v. Abbott Laboratories was a 1980 California case that established the doctrine of market share liability for personal injury cases. For such liability, when a drug causes personal injury and the manufacturer of the drug cannot be identified, each producer is responsible for paying the settlement in proportion to the percentage of the market they supplied. Judith Sindell and Maureen Rogers brought the case against the producers of diethylstilbestrol (DES), which their mothers had taken during pregnancy to prevent miscarriage and other complications. Sindell and Rogers alleged that their mothers' ingestions of DES during pregnancy later caused Sindell and Rogers to develop cancers at the onset of puberty, but they could not identify the specific manufacturer of the drug. The market share liability ruling in Sindell allowed millions of DES-affected individuals to seek restitution for reproductive cancers caused by prenatal exposure to DES.

William Withey Gull studied paraplegia, anorexia, and hormones as a physician in England during the nineteenth century. In addition to caring for patients, he described the role of the posterior column of the spinal cord in paraplegia, and he was among the first to describe the conditions of anorexia and of hypochondria. He also researched the effects of thyroid hormone deficiencies in women who had malfunctioning thyroid glands. Gull's research on thyroid hormone confirmed that chemicals in the body directly affect health, and he contributed to the foundation of endocrinology, the scientific field for the study of hormones.

Leon Chesley published Hypertensive Disorders in Pregnancy in 1978 to outline major and common complications that occur during pregnancy and manifest in abnormally high blood pressures in pregnant women. The book was published by Appleton-Century-Crofts in New York, New York. Chesley compiled his book as a tool for practicing obstetricians and teachers. The book focuses on preeclampsia and eclampsia, but it also describes other common and rare hypertensive diseases and disorders of pregnancy and discusses their histories, diagnoses, management plans, pathologies, and immediate and remote prognoses for mothers and fetuses. Doctors used the book and all subsequent editions to help diagnose and manage complications during pregnancy and to avoid deaths for pregnant women and fetuses.

In 1953, Raymond Greene and Katharina Dalton, who were doctors in the UK, published The Premenstrual Syndrome in the British Medical Journal. In their article, Dalton and Greene established the term premenstrual syndrome (PMS). The authors defined PMS as a cluster of symptoms that include bloating, breast pain, migraine-headache, fatigue, anxiety, depression, and irritability. The article states that the symptoms begin one to two weeks before menstruation during the luteal phase of the menstrual cycle, and they disappear upon the onset of the menstrual period. Menstruation is the monthly series of changes a woman's body undergoes in preparation for the possibility of pregnancy. Dalton and Greene described how progesterone affected women during different phases of their menstrual cycles. The paper convinced many about the phenomenon of PMS, and docotors and scientists adopted Dalton's and Green's term. The paper furthered research about the role of hormones in physiology and of conditions linked to the reproductive system.

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.