China
Africa
Explore chapters and articles related to this topic
Is the Human Embryo an Organism?
Published in Nicholas Colgrove, Bruce P. Blackshaw, Daniel Rodger, Agency, Pregnancy and Persons, 2023
Early human development is summarized in Figure 1.1. Briefly, upon sperm-egg fusion at fertilization, a single cell (the zygote) is formed (Figure 1.1A). The zygote divides rapidly, producing a number of smaller cells known as blastomeres (Figure 1.1B). By the second or third day following sperm-egg fusion, the blastomeres have formed a ball-like structure known as a morula-stage embryo (Figure 1.1C). Cell division continues, and by the fifth day, the embryo has grown to about one hundred cells and formed a fluid-filled structure known as a blastocyst (Figure 1.1E). At this stage, the first two committed cell types have arisen. The cells that make up the outer layer of the blastocyst are known as trophectoderm (TE). Inside the blastocyst is a cluster of cells, known as the inner cell mass (ICM).
Nanotechnology in Stem Cell Regenerative Therapy and Its Applications
Published in Harishkumar Madhyastha, Durgesh Nandini Chauhan, Nanopharmaceuticals in Regenerative Medicine, 2022
ESCs originate from the blastocyst stage and divide the tissue to become derivatives of germ layers, further leading to the formation of all types of cells. Transcription factors such as octamer-binding transcription factor-4 (OCT4)and SRY-related high-mobility group box protein-2 (SOX2) are responsible for the pluripotency and self-renewal nature. The blastocyst forms the inner and outer cell mass; the inner cell mass forms embryos and the external cell mass forms the placenta. Specific conditions are maintained in growing ESC lines to separate the cells from the inner cell layer of trophoblasts and transfer them to a culture dish (Bongso 2006). In 1998, Thomson isolated human ESCs and divided them into more than 200 categories of cells, which is promising for the treatment of various diseases, described in the next session of this chapter.
Implantation and Embryonic Imaging
Published in Mary C. Peavey, Sarah K. Dotters-Katz, Ultrasound of Mouse Fetal Development and Human Correlates, 2021
Mary C. Peavey, Sarah K. Dotters-Katz
The blastocyst consists of a discrete inner cell mass, within a spherical cavity lined by the trophectoderm cell layer. In humans, by the end of the third gestational week, the blastocyst begins to implant into the decidualized endometrium. In successful pregnancies, the average endometrial thickness is 17 ± 6.7 mm (8), and the distinct echogenic decidualized endometrium can be easily identified on transvaginal ultrasound, before the presence of a gestational sac. The endometrium will continue to appear thickened and echogenic from 4 to 5 weeks gestation, before the gestational sac is visible.
Optimal number of high-quality cleavage-stage embryos for extended culture to blastocyst-stage for transfer in women 38 years and older
Published in Gynecological Endocrinology, 2023
It was reported that older women’s age was associated with delayed embryonic development which was more pronounced at later stages of development [18]. Braga et al. indicated that the probability of blastocyst formation might be impaired when the morphology was compromised at the cleavage-stage [9]. It prompted that the embryologists should be careful to culture the embryos to blastocyst-stage for some patients. In the study, the cycle rate of no high-quality blastocyst obtained was 25.00% and 19.80% for extended culture to blastocyst-stage with 2 and 3 high-quality embryos on day 3. For these patients with 2 and 3 high-quality embryos on day 3, the blastocyst transfers had similar clinical pregnancy, ongoing pregnancy, and live birth rates compared with the cleavage-stage ETs with double high-quality embryos. For patients with 4 or more high-quality embryos on day 3, the blastocyst transfers had significantly higher ongoing pregnancy and live birth rates compared with that for patients with 2 and 3 high-quality embryos on day 3. Thus, we recommended transfer at the blastocyst-stage for AMA women with ≥4 high-quality embryos on day 3.
Trophectoderm non-coding RNAs reflect the higher metabolic and more invasive properties of young maternal age blastocysts
Published in Systems Biology in Reproductive Medicine, 2023
Panagiotis Ntostis, Grace Swanson, Georgia Kokkali, David Iles, John Huntriss, Agni Pantou, Maria Tzetis, Konstantinos Pantos, Helen M. Picton, Stephen A. Krawetz, David Miller
The American Society for Reproductive Medicine (ASRM) guidelines indicate that the male (as the sole or contributing factor) causes approximately 40% of all cases of infertility, while female infertility as sole factor, accounts for another 40% (Kumar and Singh 2015; Walker and Tobler 2020), along with various other uncharacterized/undetermined parental factors (Wu H et al. 2017; Colaco and Sakkas 2018). The mammalian blastocyst consists of trophectoderm cells (outer layer) that gives rise to the extra-embryonic tissues including the placenta and the inner cell mass (internal cells or ICM) that ultimately gives rise to the fetus. Hence, the trophectoderm is the first embryonic tissue to communicate directly with the endometrium during a narrow implantation window (Figure 1). Implantation and pregnancy failure may be affected by various factors including a failure of communication and synchronization between the blastocyst and endometrium (Achache and Revel 2006; Margalioth et al. 2006) caused by uterine anomalies (Taylor and Gomel 2008) and/or embryonic factors such as chromosomal aneuploidies (Harper 2018; Cimadomo et al. 2020) and abnormal gene expression (McCallie et al. 2019; Ntostis et al. 2019; Abu-Halima et al. 2020; Ntostis et al. 2021). These deficiencies can be mitigated in part, by ensuring only transfer of euploid blastocyst where implantation rates from 50%-80% are observed (Saravelos and Li 2012).
Developing a Reflexive, Anticipatory, and Deliberative Approach to Unanticipated Discoveries: Ethical Lessons from iBlastoids
Published in The American Journal of Bioethics, 2022
Rachel A. Ankeny, Megan J. Munsie, Joan Leach
In less than a week, a fertilized human egg develops from a single cell to a cluster of around 240 cells referred to as a blastocyst. Studying early stages of human development, including the various cell types in the blastocyst, has always been difficult. Animal models provide some insights but key differences in how embryos form and develop limit their relevance (Rossant and Tam 2017). While it is possible to study the cellular and molecular interplay underpinning blastocyst formation and implantation using donated human embryos, their use is limited due to technical, legal, and ethical concerns. Thus researchers have sought to generate models that recapitulate different aspects of early human development in order to shed light into this process. These models rely on human pluripotent stem cells–embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC)–to explore the formation and development of human embryos (known as embryogenesis). While researchers have been able to use pluripotent stem cells to create 3-D structures in vitro that mimic how organs such as the eye, brain, kidney, and liver develop for many years (broadly termed “organoids,” which provides part of the etymology for the neologism “iBlastoid”) (Lancaster and Knoblich 2014), extending directed differentiation of pluripotent stem cells to mimic the earliest stages of human development has only been pursued in recent years.