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Follicular or proliferative phase

Progestational or secretory phase

Gravid phase

Figure 2.12 Changes in the uterine mucosa correlated with those in the ovary. Implantation of the blastocyst has caused development of a large corpus luteum of pregnancy. Secretory activity of the endometrium increases gradually as a result of large amounts of progesterone produced by the corpus luteum of pregnancy.

the secretory or progestational phase, and the menstrual phase (Figs. 2.112.13). The proliferative phase begins at the end of the menstrual phase, is under the influence of estrogen, and parallels growth of the ovarian follicles. The secretory phase begins approximately 2 to 3 days after ovulation in response to progesterone produced by the corpus luteum. If fertilization does not occur, shedding of the endometrium (compact and spongy layers) marks the beginning of the menstrual phase. If fertilization does occur, the endometrium assists in implantation and contributes to formation of the placenta.

At the time of implantation, the mucosa of the uterus is in the secretory phase (Figs. 2.11 and 2.12), during which time uterine glands and arteries become coiled and the tissue becomes succulent. As a result, three distinct layers can be recognized in the endometrium: a superficial compact layer, an intermediate spongy layer, and a thin basal layer (Fig. 2.12). Normally, the human blastocyst implants in the endometrium along the anterior or posterior wall of the body of the uterus, where it becomes embedded between the openings of the glands (Fig. 2.12).

If the oocyte is not fertilized, venules and sinusoidal spaces gradually become packed with blood cells, and an extensive diapedesis of blood into the tissue is seen. When the menstrual phase begins, blood escapes from superficial arteries, and small pieces of stroma and glands break away. During the following 3 or 4 days, the compact and spongy layers are expelled from the

Hypsthinlomic

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M»1urjil»n Ol iQlücte (MJlBÎKM Corpus Mtflum Paseneraliftf

Uterine Mucosa

WiirtttnnlJ ihni<- Krrtiinrvvllvr- phaiwi Secrewy pli89B fcfnritloigl ;■ h,i>.-i

Figure 2.13 Changes in the uterine mucosa (endometrium) and corresponding changes in the ovary during a regular menstrual cycle without fertilization.

WiirtttnnlJ ihni<- Krrtiinrvvllvr- phaiwi Secrewy pli89B fcfnritloigl ;■ h,i>.-i

Figure 2.13 Changes in the uterine mucosa (endometrium) and corresponding changes in the ovary during a regular menstrual cycle without fertilization.

uterus, and the basal layer is the only part of the endometrium that is retained (Fig. 2.13). This layer, which is supplied by its own arteries, the basal arteries, functions as the regenerative layer in the rebuilding of glands and arteries in the proliferative phase (Fig. 2.13).

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