The luteal phase of the ovary begins after ovulation, typically lasting from days 16 to 28, and involves the production of progesterone. This hormone stimulates the uterine glands during the secretory phase of the uterus. If no embryo implants, the corpus luteum dies, leading to a cessation in progesterone production and shedding of the uterine endometrium, known as the menstrual phase or period, which occurs during days 1 to 5 of the follicular phase of the ovary. The cervix, located at the lower portion of the uterus, has hormonally regulated cervical mucus that aids in sperm entry into the uterus during midcycle due to estrogen stimulation. However, during the luteal phase, progesterone causes the cervical mucus to thicken, creating a barrier against sperm and microbes. We extend our gratitude to Dr. Lisa Mehlmann for her valuable guidance in this chapter and her assistance in creating Figures 44.31 and 44.32.

References:
Achar S, et al. Cardiac and metabolic effects of anabolic-androgenic steroid abuse on lipids, blood pressure, left ventricular dimensions, and rhythm. Am J Cardiol. 2010;106:893-901.
Coticchio G, et al. Oocyte maturation: gamete-somatic cells interactions, meiotic resumption, cytoskeletal dynamics and cytoplasmic reorganization. Hum Reprod Update. 2015;21:427-454.
Defeudis G, et al. Erectile dysfunction and its management in patients with diabetes mellitus. Rev Endocr Metab Disord. 2015; 16:213-231.
Franca LR, et al. The Sertoli cell: one hundred fifty years of beauty and plasticity. Andrology. 2016;4:189-212.
Kosaka T, et al. Is DHT production by 5alpha-reductase friend or foe in prostate cancer? Front Oncol. 2014;4:article 247.

Fertilization is a complex process occurring in the oviduct, where a series of events lead to the penetration of the oocyte by sperm. Early embryogenesis, which spans up to day 6 after fertilization, takes place in the oviduct and results in the formation of a blastocyst that eventually hatches from the zona pellucida. The placenta develops from the outer layer of the extraembryonic trophoblast and serves as an endocrine organ. It produces hormones such as hCG, progesterone, estrogens, and placental lactogen. Estrogen production requires the involvement of placental cells called syncytiotrophoblasts, as well as the fetal adrenal gland and liver, collectively referred to as the fetoplacental unit.

Pregnancy and the hormones associated with it bring about significant changes in maternal physiology. These changes include increased insulin resistance, enhanced utilization of free fatty acids by the mother, and development of the mammary glands. Estrogen, progesterone, and placental lactogen, along with maternal pituitary prolactin stimulated by placental estrogens, promote the development of mammary glands (but not lactation). Oxytocin, a hormone released by the pituitary gland, induces contractions in specific smooth muscles, including myometrial contractions during labor and myoepithelial contractions in the breasts that facilitate milk let-down in response to suckling. Menopause occurs when the ovarian reserve is depleted, leading to low levels of ovarian hormones and elevated gonadotropin levels.
23.
After ovulation the ovary enters the luteal phase (days 16–28) and produces progesterone. Progesterone stimulates secretion from the uterine glands (called the secretory phase of the uterus).
24.
In the absence of an implanting embryo the corpus luteum dies, progesterone production ceases, and the uterine endometrium is sloughed (called the menstrual phase, or period, of the uterus—this corresponds to days 1 to 5 of the follicular phase of the ovary).
25.
The cervix is the lower portion of the uterus. Cervical mucus is hormonally regulated so that at midcycle in response to estrogen, cervical mucus promotes entry of sperm into the uterus from the vagina. During the luteal phase in response to progesterone, cervical mucus becomes thick and poses a barrier to entry of sperm and microbes into the uterus.
We wish to thank Dr. Lisa Mehlmann for her advice on this chapter, and especially for help in drawing
Figures 44.31 44.32
Achar S, et al. Cardiac and metabolic effects of anabolic-androgenic steroid abuse on lipids, blood pressure, left ventricular dimensions, and rhythm. Am J Cardiol. 2010;106:893-901.
Coticchio G, et al. Oocyte maturation: gamete-somatic cells interactions, meiotic resumption, cytoskeletal dynamics and cytoplasmic reorganization. Hum Reprod Update. 2015;21:427-454.
Defeudis G, et al. Erectile dysfunction and its management in patients with diabetes mellitus. Rev Endocr Metab Disord. 2015; 16:213-231.
Franca LR, et al. The Sertoli cell: one hundred fifty years of beauty and plasticity. Andrology. 2016;4:189-212.
Kosaka T, et al. Is DHT production by 5alpha-reductase friend or foe in prostate cancer? Front Oncol. 2014;4:article 247.
26.
Fertilization is a complex series of events that occur in the oviduct and lead to penetration of the oocyte by sperm.
27.
Early embryogenesis (up to day 6 after fertilization) occurs in the oviduct and gives rise to a blastocyst that hatches from the zona pellucida.
28.
The placenta develops from the outer extraembryonic trophoblast. The endocrine function of the placenta includes production of hCG, progesterone, estrogens, and placental lactogen. Estrogen production requires placental cells (syncytiotrophoblasts) as well as the fetal adrenal and liver—collectively called the fetoplacental unit.
29.
Pregnancy and the hormones of pregnancy induce major changes in maternal physiology, including an increase in insulin resistance, an increase in the use of free fatty acids by the mother, and development of the mammary glands. Mammary gland development (but not lactation) is promoted by estrogen, progesterone, and placental lactogen but also by maternal pituitary prolactin, whose secretion is stimulated by placental estrogens.
30.
Oxytocin is a pituitary hormone that promotes contraction of certain smooth muscles, including myometrial contractions during labor and myoepithelial contractions in the breasts that lead to let-down of milk in response to suckling.
31.
Menopause results from exhaustion of the ovarian reserve and is characterized by low ovarian hormone and elevated gonadotropin levels.