M9 V2

Summary

This presentation delves into the ovarian cycle, explaining its four major functions: gamete production, ovulation, hormone secretion, and follicle maturation. It describes the two main phases of the ovarian cycle—the follicular phase (Days 1-14) and luteal phase (Days 15-28)—with emphasis on the development of follicles and the role of hormones. Ovulation occurs around day 14, releasing a secondary oocyte. The presentation also covers the life cycle of follicles, the formation of the corpus luteum, and its role in pregnancy or menstruation. The session concludes by hinting at the next topic: hormonal control of ovarian function.

Takeaways

• 😀 The ovary has four major functions: production of gametes (oogenesis), maturation and expulsion of oocytes (ovulation), and secretion of hormones like estrogen, progesterone, and inhibin.
• 😀 The ovarian cycle consists of two phases: the follicular phase (days 1-14) and the luteal phase (days 15-28), during which follicles mature, ovulation occurs, and the corpus luteum develops.
• 😀 Only 10-15% of women have a 28-day cycle; the length of the follicular phase can vary, but the luteal phase generally stays constant at 14 days.
• 😀 At birth, a female has 1-2 million eggs, which decrease to about 300,000 by puberty and less than 1,000 by menopause. Only about 400 eggs are released during a woman's lifetime.
• 😀 Oocytes exist within follicles, starting as primordial follicles before birth, and progress through primary, secondary, and antral stages as they mature.
• 😀 The primary follicle forms when granulosa cells surround the oocyte, and the zona pellucida forms around the oocyte.
• 😀 Granulosa cells communicate with the oocyte through gap junctions, allowing mutual guidance during follicle development.
• 😀 At the secondary and preantral stages, granulosa cells produce estrogen through collaboration with the surrounding theca cells, which synthesize androgens.
• 😀 The antrum (fluid-filled cavity) forms in the follicle as it matures. 10-25 follicles begin to develop at the start of each menstrual cycle, but only one becomes dominant.
• 😀 Atresia, or apoptosis, affects most follicles at every stage of development, with 99.99% of ovarian follicles undergoing atresia before reaching maturity.
• 😀 Ovulation occurs when the dominant follicle bursts, releasing the secondary oocyte into the peritoneal cavity, assisted by follicular fluid, which provides protection and nourishment.

Q & A

What are the four major functions of the ovary?

The four major functions of the ovary are the production of gametes (oogenesis), maturation and expulsion of the oocyte (ovulation), secretion of hormones (including estrogen, progesterone, and inhibin), and the development of the corpus luteum.

What phases make up the ovarian cycle?

The ovarian cycle consists of two phases: the follicular phase (days 1 to 14) during which follicles grow and ovulation occurs, and the luteal phase (days 15 to 28) during which the corpus luteum is active.

What is the typical length of the follicular phase and luteal phase?

The follicular phase can vary in length, but the luteal phase typically stays constant at 14 days.

How many oocytes are released during a woman's lifetime?

Approximately 400 oocytes are released during a woman's lifetime.

What is a primordial follicle?

A primordial follicle is an early stage of follicle development that contains a primary oocyte arrested in prophase I, surrounded by a single layer of granulosa cells.

How does the process of atresia affect ovarian follicles?

Atresia is a form of apoptosis where many ovarian follicles, including non-dominant ones, undergo degeneration at various stages of development. Around 99.99% of the follicles present at birth undergo atresia.

What happens to the granulosa cells during follicle development?

During follicle development, granulosa cells proliferate to form a stratified epithelium around the oocyte. They work together with the theca cells to synthesize estrogen, converting androgens into estrogen.

What is the role of the cumulus oophorus during ovulation?

The cumulus oophorus is a mound of granulosa cells that projects into the antrum of the mature follicle and surrounds the oocyte. It helps the oocyte move during ovulation and is involved in the processes leading to the expulsion of the oocyte into the peritoneal cavity.

What triggers the process of ovulation?

Ovulation is triggered by luteinizing hormone (LH), which initiates a series of processes leading to the rupture of the follicle and the release of the secondary oocyte.

What happens to the corpus luteum after ovulation if the oocyte is not fertilized?

If the oocyte is not fertilized, the corpus luteum degenerates after approximately 10 days, and its hormonal output stops. It eventually forms a scar called the corpus albicans.