Uterine wall

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The menstrual cycle causes a series of changes each month (under normal circumstances) that are produced by the action of hormones in the female reproductive organs. It involves two cycles that interact and overlap; the ovarian cycle and the uterine cycle.

• The ovarian cycle goes through three phases: follicular, ovulatory and luteal. All of these phases allow the maturation and release of the ovum.
• The uterine cycle equally has three phases: menstruation, proliferative and secretory. The uterine phases act to prepare the uterus for possible fertilization and pregnancy.

Thus, cyclic changes of the uterine wall (endometrium) during the menstrual cycle are represented by the these three phases.

Proliferative phase

In the proliferative phase (days 1-14) of the uterine cycle, the endometrium prepares for implantation. This phase corresponds to the follicular phase of the ovarian cycle (follicular maturation) and is regulated by ovarian estrogen secretion. In the proliferative phase, both the endometrial glands and stroma proliferate in response to increasing levels of estrogen.

You can review all the structures that play an important role in this phase in the image gallery below:

Increase in progesterone levels concludes the proliferative phase and the endometrium passes into the secretory phase.

Secretory phase

In the secretory phase (days 14-28), the endometrium becomes a nutritionally rich environment for implantation of the fertilized egg. This phase corresponds to the luteal phase of the ovarian cycle (functional activity of the corpus luteum) and is regulated by progesterone secretion. In this phase, the endometrium thickens considerably, while the endometrial glands become dilated and tortuous (corkscrew) and produce a secretion rich in glycogen.

If no egg is fertilized, the endometrium is shed, signifying the start of menstrual phase. Hormone production by the ovary declines, as the corpus luteum begins to degenerate.

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