Embryologie: Document en anglais: First Week of Development: Ovulation to Implantation
At puberty, the female begins to undergo regular monthly cycles. These sexual cycles are controlled by the hypothalamus. Gonadotropin-releasing hormone (GnRH), produced by the hypothalamus, acts on cells of the anterior pituitary gland, which in turn secrete gonadotropins. These hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), stimulate and control cyclic changes in the ovary.
[...] The results of fertilization are restoration of the diploid number of chromosomes, determination of chromosomal sex, and initiation of cleavage. Cleavage is a series of mitotic divisions that results in an increase in cells, blastomeres, which become smaller with each division. After three divisions, blastomeres undergo Compaction to become a tightly grouped ball of cells with inner and outer layers. Compacted blastomeres divide to form a 16-cell morula. As the morula enters the uterus on the third or fourth day after fertilization, a cavity begins to appear, and the blastocyst forms. [...]
[...] This process, Compaction, segregates inner cells, which communicate extensively by gap junctions, from outer cells. Approximately 3 days after fertilization, cells of the compacted embryo divide again to form a 16-cell morula (mulberry). Inner cells of the morula constitute the Inner cell mass, and surrounding cells compose the Outer cell mass. The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the Trophoblast, which later contributes to the placenta. Blastocyst Formation About the time the morula enters the uterine cavity, fluid begins to penetrate through the zona pellucida into the intercellular spaces of the inner cell mass. [...]
[...] However, she has been having difficulty becoming pregnant. What is likely to be the problem, and what would you suggest? [...]
[...] The zona pellucida has disappeared, allowing implantation to begin. In the human, trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa on about the sixth day (Fig C). New studies suggest that L-selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium mediate initial attachment of the blastocyst to the uterus. Selectins are carbohydrate-binding proteins involved in interactions between leukocytes and endothelial cells that allow leukocyte “capture” from flowing blood. [...]
[...] Chapter 3 First Week of Development: Ovulation to Implantation Ovarian Cycle At puberty, the female begins to undergo regular monthly cycles. These sexual cycles are controlled by the hypothalamus. Gonadotropin-releasing hormone (GnRH), produced by the hypothalamus, acts on cells of the anterior pituitary gland, which in turn secrete gonadotropins. These hormones, follicle-stimulating hormone (FSH) and luteinizing hormone stimulate and control cyclic changes in the ovary. At the beginning of each ovarian cycle to 20 primary (preantral) stage follicles are stimulated to grow under the influence of FSH. [...]
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