Segmentación y Nidación

Segmentation and Nidation

• In identical twins, cell segmentation occurs very early. In conjoined twins, it occurs later.
• After ovulation, the zygote divides mitotically, increasing the number of cells (blastomeres). Early cells share the initial cytoplasm, which diminishes as cell division continues. This segmentation process stops unless implantation occurs, as the cytoplasm is depleted.
• The distance from the fallopian tube is significant in estimating time frames.
• Zygote segmentation into blastomeres starts about 30 hours after fertilization.
• Day 0: Zygote (single cell)
• Days 1-4: Morula (16-32 cells, blackberry-like)
• Days 4-5: Blastocyst/Blastula/Blastocele
• The structure changes as fluid fills the morula becoming a blastula.

Blastocyst Formation

• The blastocyst (immature form/blastula + cyst cavity) appears around day 5, floating freely in the uterine cavity.
• The outer layer is the trophoblast, crucial for implantation, initiating contact with the mother's body.
• The inner cell mass (ICM) is the true developing embryo/ early embryonic disk.
• The ICM will develop into the embryo itself, while the trophoblast is not part of the developing embryo, but an essential support structure. It will become the placenta.

Second Week Development

• Implantation begins around day 6, with the blastocyst embedding into the uterine lining.
• The trophoblast differentiates into two layers, the cytotrophoblast and the syncytiotrophoblast.
• The inner cell mass (ICM) differentiates into two layers, the hypoblast and epiblast, resulting in a bilaminar embryonic disc.
• The amniotic sac and yolk sac form.

Este cuestionario explora el proceso de segmentación y formación del blastocisto. Incluye datos sobre la división celular del cigoto y su desarrollo en un embrión. Además, se discuten las diferencias en la segmentación entre gemelos idénticos y gemelos unidos.