Test Yourself Before You Continue

1. Compare the structure and contents of a primary follicle, secondary follicle, and graafian follicle.

2. Define ovulation and describe the changes that occur in the ovary following ovulation in a nonfertile cycle.

3. Describe oogenesis and explain why only one mature ovum is produced by this process.

4. Compare the hormonal secretions of the ovarian follicles with those of a corpus luteum.

First meiotic division

First polar body degenerates

Secondary oocyte (23 chromosomes)

Spermatozoon fertilizes oocyte

Second meiotic division

Second polar body degenerates


■ Figure 20.32 Oogenesis. During meiosis, each primary oocyte produces a single haploid gamete. If the secondary oocyte is fertilized, it forms a second polar body and its nucleus fuses with that of the sperm cell to become a zygote.

Since one releasing hormone can stimulate the secretion of both FSH and LH, one might expect always to see parallel changes in the secretion of these gonadotropins. This, however, is not the case. FSH secretion is slightly greater than LH secretion during an early phase of the menstrual cycle, whereas LH secretion greatly exceeds FSH secretion just prior to ovulation. These differences are believed to result from the feedback effects of ovarian sex steroids, which can change the amount of GnRH secreted, the pulse frequency of GnRH secretion, and the ability of the anterior pituitary cells to secrete FSH and LH. These complex interactions result in a pattern of hormone secretion that regulates the phases of the menstrual cycle.

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Essentials of Human Physiology

Essentials of Human Physiology

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  • mathew dunn
    Why only one mature ovum is produced by oogenesis process?
    8 years ago

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