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In human sexuality, the refractory period is usually the recovery phase after orgasm during which it is physiologically impossible for males to have additional orgasms. [1] [2] This phase begins immediately after ejaculation and lasts until the excitement phase of the human sexual response cycle begins anew with low-level response.
Early development of the human embryo from ovulation through implantation. The zygote undergoes several rounds of mitosis. After the 3rd cleavage division, the embryo begins the process of compaction, which, in human, is only completed when the embryo consists of 8-16 cells, [7] [8] then becoming known as the morula.
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.
At the 16–cell stage the compacted embryo is called a morula. [14] [15] Once the embryo has divided into 16 cells, it begins to resemble a mulberry, hence the name morula (Latin, morus: mulberry). [16] Concomitantly, they develop an inside-out polarity that provides distinct characteristics and functions to their cell-cell and cell-medium ...
Experiments with implantation in mice show that hormonal induction, superovulation and artificial insemination successfully produce preimplantation mouse embryos. In the mice, ninety percent of the females were induced by mechanical stimulation to undergo pregnancy and implant at least one embryo. [ 17 ]
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.
It develops following cleavage of the zygote after fertilization. [2] [3] It is the first fluid-filled cavity or lumen formed as the embryo enlarges, [4] and is the essential precursor for the differentiated gastrula. [5] [page needed] In the Xenopus a very small cavity has been described in the two-cell stage of development. [6]
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.