Menstrual stage, Ovulation, Proliferative stage, Endometrium, Secretory stage

The menstrual cycle, sometimes referred to as the uterine cycle, is hormonally controlled by estrogens and progesterone secreted by the ovary. It is normally divided into three stages: menstrual, proliferative, and secretory. The endometrial changes correlate with hormonal and ovarian changes.

Figure 10.24

Figure 10.25

Menstrual stage (menses): Approximately days 1 to 5. Sloughing off of the thick functional layer of the endometrial lining of the uterus, accompanied by bleeding.

Proliferative stage: Approximately days 6 to 14. Under the influence of estrogens produced by the growing follicle of the ovary, the endometrium is repaired, glands and blood vessels proliferate, and the endometrium thickens. Ovulation occurs at the end of this stage.

Secretory stage: Approximately days 15 to 28. Under the influence of progesterone produced by the corpus luteum, the vascular supply to the endometrium increases further. The glands increase in size and begin to secrete nutrient substances to sustain a developing embryo, if present, until implantation can occur. If fertilization has occurred, the embryo will produce a hormone much like LH, which will maintain the function of the corpus luteum. Otherwise, as the corpus luteum begins to deteriorate, lack of ovarian hormones in the blood causes blood vessels supplying the endometrium to kink and become spastic, setting the stage for menses to begin by the 28th day.

Although the foregoing explanation assumes a classic 28-day cycle, the length of the menstrual cycle is highly variable, sometimes as short as 21 days or as long as 38. Only one interval is relatively constant in all females: the time from ovulation to the onset of menstruation is almost always 14 days.

Figure 10.26 Endometrial Changes

H) Questions (Female)

1. What is the gonad in the female reproductive system?

2. What is the inner layer of the uterus called?

3. What happens to estrogen and progesterone levels just prior to menstruation?

4. The uterus is connected to the ovaries by what structure?

5. What three hormones are at elevated levels just prior to ovulation?

6. What is the name for the expulsion of the secondary oocyte from the ovary?

7. What is the deepest layer of the endometrium called?

8. What are the milk producing glands of the breast called?

9. Trace the pathway of milk from the mammary glands to expulsion.

10. Ectopic pregnancies are those that occur outside of the endometrial layer of the uterus. Provide an explanation for how pregnancies may occur in the uterine tube or in the abdominopelvic cavity.