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Human fertilization is the union of an egg and sperm, occurring primarily in the ampulla of the fallopian tube. [1] The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the 19th century. [2]
Embryonic age: Week nr 1. 0 (whole) weeks old. 1–7 days from fertilization. Fertilization of the ovum to form a new human organism, the human zygote. (day 1 of fertilization [1]) The zygote undergoes mitotic cellular divisions, but does not increase in size. This mitosis is also known as cleavage. A hollow cavity forms marking the blastocyst ...
Chart of human fetal development, U.S. National Library of Medicine (NLM) U.K. Human Fertilisation and Embryology Authority (HFEA), regulatory agency overseeing the use of gametes and embryos in fertility treatment and research "Child Safety tips: 10 Expert Tips for Keeping Your Kids Safe"
The average age of a girl's first period is 12 to 13 (12.5 years in the United States, [6] 12.72 in Canada, [7] 12.9 in the UK [8]) but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, which declines to 50% in the third year, and to 10% by the sixth. [9]
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.
In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell . [2] The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences.
Timeline of human fertilization. In humans, pregnancy can be defined clinically, biochemically or biologically. Clinically, pregnancy starts from first day of the mother's last period. [4] Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL. [5]
Human reproduction usually involves internal fertilization by sexual intercourse. In this process, the male inserts his penis into the female's vagina and ejaculates semen, which contains sperm. A small proportion of the sperm pass through the cervix into the uterus and then into the fallopian tubes for fertilization of the ovum. Only one sperm ...