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Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus.
3. Morula. The ball of cells formed after the multiple divisions is called a morula. It consists of about 16-32 cells in a ball within a translucent, elastic layer called the zona pellucida. It will then undergo compaction which is a process where the cells bind firmly together and continue to develop into a blastocyst. [8] 4. Blastocyst
The germinal stage refers to the time from fertilization, through the development of the early embryo, up until implantation. The germinal stage is over at about 10 days of gestation. [2] The zygote contains a full complement of genetic material with all the biological characteristics of a single human being, and develops into the embryo.
Embryonic stem cells (ESCs) are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre-implantation embryo. [1] [2] Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells.
In humans, blastocyst formation begins about five days after fertilization when a fluid-filled cavity opens up in the morula, the early embryonic stage of a ball of 16 cells. The blastocyst has a diameter of about 0.1–0.2 mm and comprises 100-200 cells following 7-8 rounds of cleavage (cell division without cell growth).
Most men should start getting screened when they reach 50, and Black men, people with a family history of prostate cancer, and others with a higher risk should get screened starting at 40.
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.
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