Uterus at Time of Implantation

The wall of the uterus consists of three layers: (a) endometrium or mucosa lining the inside wall; (b) myometrium, a thick layer of smooth muscle; and (c) perimetrium, the peritoneal covering lining the outside wall (Fig. 2.11). From puberty (11-13 years) until menopause (45-50 years), the endometrium undergoes changes in a cycle of approximately 28 days under hormonal control by the ovary. During this menstrual cycle, the uterine en-dometrium passes through three stages, the follicular or proliferative phase,

First Week Human Development

Figure 2.11 Events during the first week of human development. 1, Oocyte immediately after ovulation. 2, Fertilization, approximately 12 to 24 hours after ovulation. 3, Stage of the male and female pronuclei. 4, Spindle of the first mitotic division. 5, Two-cell stage (approximately 30 hours of age). 6, Morula containing 12 to 16 blastomeres (approximately 3 days of age). 7, Advanced morula stage reaching the uterine lumen (approximately 4 days of age). 8, Early blastocyst stage (approximately 4.5 days of age). The zona pellucida has disappeared. 9, Early phase of implantation (blastocyst approximately 6 days of age). The ovary shows stages of transformation between a primary follicle and a preovulatory follicle as well as a corpus luteum. The uterine endometrium is shown in the progestational stage.

Figure 2.11 Events during the first week of human development. 1, Oocyte immediately after ovulation. 2, Fertilization, approximately 12 to 24 hours after ovulation. 3, Stage of the male and female pronuclei. 4, Spindle of the first mitotic division. 5, Two-cell stage (approximately 30 hours of age). 6, Morula containing 12 to 16 blastomeres (approximately 3 days of age). 7, Advanced morula stage reaching the uterine lumen (approximately 4 days of age). 8, Early blastocyst stage (approximately 4.5 days of age). The zona pellucida has disappeared. 9, Early phase of implantation (blastocyst approximately 6 days of age). The ovary shows stages of transformation between a primary follicle and a preovulatory follicle as well as a corpus luteum. The uterine endometrium is shown in the progestational stage.

Maturation of follicle Ovulation Corpus luteum

Corpus luteum of pregnancy

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