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PinkMonkey Online Study Guide-Biology

The ovum released in the ovulatory phase may or may not be fertilized. If the ovum is fertilized, it becomes embedded in the endometrium (implantation). In this case the corpus luteum remains to secrete progesterone which help the embryo to grow within the uterus. If the ovum is not fertilized, the corpus luteum disintegrates and the progesterone level falls sharply. Fourteen days after ovulation, unless fertilization occurs, menstruation begins again.


The cyclic changes in the female reproductive system of non-primate mammals is called estrous cycle. It differs from the menstrual cycle in two respects: (1) there is no menstruation or blood flow at the end of estrous cycle; (2) there is a strong sex urge in the female animal, and the animal is said to be in ’heat’ and ready to receive the male only during the short period of estrous or heat. This part of the season is called breeding period, the rest part of the cycle forms the non-breeding period. The estrous period may extend from few hours to few days in different animals. The animals may be monoestrous (e.g., deer, sheep) or polyestrous (e.g., cat, dog). The hormonal regulation of the estrous cycle is similar to that of the menstrual cycle.

Hormonal Control of Menstrual Cycle

The following hormones regulate the menstrual cycle. (Figure 24.7)These hormones have profound effects on the ovaries and the uterus.

(1) The anterior pituitary gland produces two gonadotrophic hormones: the follicle stimulating hormone (FSH) and the luteinizing hormone (LH). FSH stimulates the ovarian follicle to mature and secondly, it stimulates the follicle to produce estrogen. The estrogen brings about healing and repair of uterine wall (endometrium) following menstruation.

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Figure 24.7 Hormonal Control of menstrual cycle

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Table of Contents

24.0 Introduction
24.1 Human reproduction
24.2 Female reproductive cycle
24.3 Embryonic Development

Chapter 25


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