Early Pregnancy
Michele Kiely in Reproductive and Perinatal Epidemiology, 2019
Ectopic implantation is virtually never observed in non-human species. Implantation, like fertilization, is complex and multistaged. The conceptus imbeds in the endometrium, which is the heavily-vascularized tissue that lines the uterus. There it develops connections to the maternal blood supply. This intimate contact is established even though the conceptus carries genes of the father and thus is antigenically foreign to the mother. Once the conceptus is able to acquire nutrients from maternal blood, it grows rapidly. Still, the embryo is in jeopardy until it can intercept and take control of the mother’s hormone regulation. The conceptus does this by producing hCG (human chorionic gonadotropin). To understand the action of hCG first requires some discussion of hCG’s target: the corpus luteum. The corpus luteum (or “yellow body”) is a temporary mass of yellow tissue on the surface of the ovary, formed each cycle from the remnants of the ruptured follicle. The corpus luteum is responsible for production of progesterone (literally, the hormone “supporting pregnancy”). Progesterone stimulates the endometrial lining of the uterus so that it will be primed for implantation. The second half of the menstrual cycle (from ovulation to onset of next menses) is called the luteal phase because the woman’s hormonal milieu is dominated by progesterone from the corpus luteum. The length of the luteal phase is relatively predictable: by 7 to 10 days after ovulation, the corpus luteum begins to regress and progesterone levels begin to fall. If there is no pregnancy, the corpus luteum ceases to function by about the fourteenth day after ovulation. Progesterone production ends, and the uterine lining is shed in menstrual bleeding. By the seventh or eighth day after ovulation, just as the corpus luteum is in its prime, the conceptus is reaching the early blastocyst stage and is ready to implant. It is still nearly microscopic, consisting of roughly a hundred cells arranged in the shape of a hollow ball. More than 90% of these cells are trophoblasts, which are the cells that will form the placenta. Trophoblasts are also the source of hCG. hCG is the embryo’s imitation of luteinizing hormone (LH).
Natural family planning methods: fertility awareness
Suzanne Everett in Handbook of Contraception and Sexual Health, 2020
This causes the reduction of FSH so that further ovum development is inhibited, the endometrium becomes thickened ready for implantation and the cervical glands produce mucus favourable to sperm penetration. As the ovum ripens, the level of oestrogen rises, causing the pituitary gland to produce luteinizing hormone (LH. This causes the follicle to rupture, releasing the ovum into the fallopian tube; this is known as ovulation. Rising oestrogen levels cause the cervix to soften and rise upwards and the os to open. The empty follicle becomes the corpus luteum, which secretes the hormone progesterone. This part of the menstrual cycle is known as the luteal phase. Progesterone causes the basal body temperature to rise during the luteal phase after ovulation. The pituitary gland is now inhibited from producing LH and FSH so that further ovulation is prevented. Following ovulation cervical mucus becomes thickened and sticky, making sperm penetration difficult. The cervix becomes firm and the os closes. If the ovum is fertilised, then the corpus luteum will continue to produce progesterone throughout early pregnancy. However, if the ovum is not fertilised then the corpus luteum will disintegrate, the level of progesterone will drop and menstruation will occur. The shift in basal body temperature, position of the cervix and change in cervical mucus are all used as indicators for natural family planning and fertility awareness to assess when a woman is fertile.
Ovarian and menstrual cycles
David M. Luesley, Mark D. Kilby in Obstetrics & Gynaecology, 2016
After the release of the oocyte–cumulus complex the follicular antrum is filled with blood and new blood vessels forms. The theca-lutein cells become full of cholesterol (luteinised) and the resulting structure is called a corpus luteum. The corpus luteum produces oestrogen, progesterone (P4) and inhibin A in response to LH pulses. These in turn suppress FSH and LH secretion by the pituitary. In the face of declining FSH and LH levels the corpus luteum functions for only about 10 days, with peak activity at about 7 days after ovulation (mid-luteal peak of progesterone on day 21 of a 28-day cycle). It then enters into an apoptosis and regression phase of about 4 days if pregnancy does not occur. In the absence of pregnancy, the corpus luteum has a fairly predictable life span of 14 days. The falling oestradiol and progesterone levels lead to apoptosis and shedding of the endometrium. The falling ovarian steroid levels release the hypothalamus and pituitary from the negative feedback effect, with a subsequent increase in FSH levels and ensuring a new cycle of recruitment of secondary follicles. The luteo-follicular transition phase is characterised by increasing FSH levels, low oestradiol and progesterone levels and high inhibin B secreted by the granulosa cells of recruited follicles. If pregnancy occurs the hCG produced by the trophoblast of the implanting embryo rescues the corpus luteum from apoptosis and atresia, enabling the corpus luteum to function and produce progesterone till 10–12 weeks’ gestation when the placenta takes over this function.
Studies on reactivation of regressing bonnet monkey corpus luteum on day 1 of menses: A pilot study
Published in Systems Biology in Reproductive Medicine, 2013
Padmanaban S. Suresh, Rudraiah Medhamurthy
Studies on functional characteristics of the regressing primate corpus luteum (CL) to luteotrophic stimulus on day 1 of the non-fertile menstrual cycle are scarce. Recombinant human luteinizing hormone (rhLH) (20 IU/Kg BW; n = 10) or human chorionic gonadotropin (hCG) (180 IU; n = 6) were administered intravenously to female bonnet monkeys on day 1 of menses. Exogenous treatment of rhLH or hCG caused a significant increase in circulating progesterone (P4) levels 2-4 hours post treatment (P
Effect of Cadmium on Cellular Ultrastructure in Mouse Ovary
Published in Ultrastructural Pathology, 2015
Ying Wang, Xuejuan Wang, Yanwu Wang, Rong Fan, Chao Qiu, Shan Zhong, Lei Wei, Daji Luo
This study aimed at analyzing the cytotoxicity and pathological effects of cadmium on the ovary. Our studies revealed that cadmium was deposited in the mouse ovary after 8 d cadmium injection in vivo. Also, the increase in the rate of body weight was slowed, while the gonadosomatic index was reduced in the CdCl2 group, compared with the control group. Meanwhile, cadmium affected the maturation of follicles, the degradation of corpus luteum, the arrangement of follicles and corpus luteum, and increased the number of atresia follicles. Besides, under the electron microscope, chromatin margination, karopyknosis, swelling of mature cisternae of Golgi apparatus, mitochondrial cristae disappearance, and swelling of the rough endoplasmic reticulum can be observed in the CdCl2 group mice. Collectively, our findings elucidated the morphological mechanism that the exposure of cadmium changed the ultrastructure of cells in ovary tissues.
The history of natural progesterone, the never-ending story
Published in Climacteric, 2018
The term progesterone should only be used for the natural hormone produced by the ovaries or included in a registered drug. The modern history of progesterone begins with the first book-length description of the female reproductive system including the corpus luteum and later with the Nobel Prize winner, Adolf Butenandt who took a crucial step when he succeeded in converting pregnanediol into a chemically pure form of progesterone, the corpus luteum hormone. The deficient production of progesterone was shown first to be the cause of the luteal-phase deficiency responsible for infertility and early pregnancy loss due to inadequate secretory transformation of the endometrium. Later, progesterone was confirmed to be the best and safest method of providing luteal-phase support in assisted reproductive technology. Progesterone provides adequate endometrial protection and is suggested to be the optimal progestagen in menopausal hormone therapy in terms of cardiovascular effects, venous thromboembolism, probably stroke and even breast cancer risk. Neuroprotective effects of progesterone have also been demonstrated in several of experimental models including cerebral ischemic stroke and Alzheimer’s disease. Vaginal progesterone was shown to decrease the risk of preterm birth in women with a mid-trimester sonographic short cervix and to improve perinatal outcomes in singleton and twin gestations.
Related Knowledge Centers
- Estrogens
- Luteinizing Hormone
- Oogenesis
- Ovulation
- Progesterone
- Granulosa Cells
- Luteal Cells