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The blastocyst stage occurs between 5 and 9 days after conception. During embryonic development, after fertilization (approximately 5–6 days in the human), the cells of the morula begin to undergo cell differentiation, and the morula changes into the blastocyst by pumping fluid to grow a lumen.
Implantation bleeding occurs between 7 and 14 days after fertilization, [57] and is a small amount of light vaginal bleeding or spotting that can occur in early pregnancy due to the blastocyst penetrating the lining of the uterus during implantation.
The trophoblast (from Greek trephein: to feed; and blastos: germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans. [1] They provide nutrients to the embryo and develop into a large part of the placenta.
The blastocyst reaches the uterus at roughly the fifth day after fertilization. The blastocyst hatches from the zona pellucida allowing the blastocyst's outer cell layer of trophoblasts to come into contact with, and adhere to, the endometrial cells of the uterus.
Cavitation is the formation of the blastocoel, a fluid-filled cavity that defines the blastula, or in mammals the blastocyst. [1] After fertilization , cell division of the zygote occurs which results in the formation of a solid ball of cells ( blastomeres ) called the morula .
After fertilization, an embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body. See egg for a discussion of eggs of oviparous animals. The egg cell's cytoplasm and mitochondria are the sole means the egg can reproduce by mitosis and eventually form a blastocyst after fertilization.
Once the blastocyst is formed, it undergoes implantation into the endometrium. [4] During implantation the blastocyst, which contains the inner cell mass, undergoes cellular differentiation into the two layers of the bilaminar embryonic disc. One of which is the epiblast, also known as the primitive ectoderm.
In humans, blastomere formation begins immediately following fertilization and continues through the first week of embryonic development. About 90 minutes after fertilization, the zygote divides into two cells. The two-cell blastomere state, present after the zygote first divides, is considered the earliest mitotic product of the fertilized ...