The embryonic period
Frank J. Dye in Human Life Before Birth, 2019
Before the human embryo leaves the fallopian tube to enter the uterine cavity, it undergoes a stage referred to as the morula. The morula is a stage in animal development characterized by a solid ball of blastomeres (Figure 8.2). During mammalian development, blastomeres undergo a process called compaction. Until this stage, the individual blastomeres are easily discernible—like members of a cluster of grapes. During compaction, however, the association of the blastomeres becomes so intimate that it is no longer possible to make out the individual blastomeres using an ordinary light microscope. While the cells are intimately associated, they form among themselves two types of connections, or cell junctions. These cell junctions allow the next stage of development, the blastocyst, to emerge.
Reproductive system
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
Following fertilisation, the zygote undergoes a process of rapid mitotic divisions known as cleavage. The first cleavage division produces two identical cells called blastomeres that continue to divide to produce four cells, then eight cells and so on. By day 4, the zygote (or pre-embryo) has become a cluster of between 16 and 32 cells forming a ball-shaped structure known as the morula (Latin for ‘mulberry’). As the morula progresses along the fallopian tube towards the uterus, it begins to hollow out to produce a fluid-filled space called the blastocoel or blastocyst cavity. This contains a mass of cells known as a blastocyst that will eventually develop into the embryo. At about day 5, the blastocyst frees itself from the layer of cells that surround it (the zona pellucida) and floats freely in the uterus. During the following days, it presses up against the endometrium and begins the process of implantation. Enzymes break down endometrial cells and capillary walls, which allows the blastocyst to penetrate and implant into the endometrium. The blastocyst continues to secrete human chorionic gonadotropin (hCG) to ensure the corpus luteum maintains production of progesterone until the placenta can take over. Implantation is complete by about 12 days after fertilisation and, over the next few weeks, the placenta (Latin for ‘flat cake’) begins to develop.
The Helminths
Donald L. Price in Procedure Manual for the Diagnosis of Intestinal Parasites, 2017
Members of the genus Trichostrongylus are parasites of the digestive tract of ruminants. T. orientalis is a relatively common parasite of man in the orient, especially in agricultural areas of Japan, Taiwan, and Korea. Other species more rarely are accidental parasites of man. The eggs (Plate 11:5; Plate 34:7–9) are thin-shelled, elongated, and may be generally ellipsoidal, slightly tapering toward one end, or sometimes both ends, and measure about 85 × 35 μm. Typically, the embryo is developed to near the morula stage. Infections diagnosed by finding eggs in fecal specimens may be spurious infections resulting from the ingestion of food contaminated with dung from an infected reservoir host, especially when many eggs are present. Rarely, juveniles of Trichostrongylus are seen in fecal specimens.
Differences in secretome in culture media when comparing blastocysts and arrested embryos using multiplex proximity assay
Published in Upsala Journal of Medical Sciences, 2018
Karin E. Lindgren, Fatma Gülen Yaldir, Julius Hreinsson, Jan Holte, Karin Kårehed, Inger Sundström-Poromaa, Helena Kaihola, Helena Åkerud
The most commonly used technique for selecting embryos for transfer is based on embryo morphology (2), where timing of development is studied. This is, however, a non-standardized method and limited due to inter-individual variability, since evaluation of morphology is performed manually. In previous studies, the impact of using time-lapse photography has been shown to correlate well with increased success rates after IVF treatment (48). Timing to morula formation has been shown to be crucial for the ability of the embryo to develop into a blastocyst (24), and our results are in agreement with this. We also conclude that timing to morula formation is of major importance as regards the formation of high-quality blastocysts. We also showed that the levels of protein expression and time to morula formation were significantly correlated. The protein levels of VEGF-A, IL-6, and EMMPRIN were significantly higher in the embryos that had a shorter time to morula formation.
Biology of Cancer; From Cellular Cancerogenesis to Supracellular Evolution of Malignant Phenotype
Published in Cancer Investigation, 2018
Several studies suggest that cancerogenesis would be caused by inadequate embryological reprogramming of some cells (11,12,14). Embryogenesis is the process by which embryo develops towards fetus. It starts from a single cell/zygote that generate through mitosis/cleavage the blastocyst. This early structure contains two distinct developmental lines, represented centrally by inner cell mass (embryoblast, generating endoderm, mesoderm, and ectoderm) and peripherally by trophoblast (generating placenta) (20).
Sex-discordant monochorionic dizygotic twins: a case report
Published in Journal of Obstetrics and Gynaecology, 2018
Sheila Vázquez Rodríguez, Loida Pamplona Bueno, Farida Akhoundova Sanoyan, Ramiro Quiroga de la Cruz, Vicente Diago Almela, Alfredo Perales Marín
The formation of the placenta in MZ twins depends on the cleavage stage. If the separation of the egg occurs before 72 hours after fertilisation, when it is still in a morula stage, the result is a dichorionic diamniotic pregnancy. The blastocyst develops from day 4 after fertilisation and when it separates at this stage, the results can be a MC diamniotic or monoamniotic pregnancy (Hall 2003).
Related Knowledge Centers
- Cell Cycle
- Blastomere
- Embryology
- Blastocyst
- Zygote
- Cell
- Fertilisation
- Blastulation
- Yolk
- Polarity In Embryogenesis