Gametogenesis: Stages of Oogenesis

Introduction to Experiment

The simulation “Gametogenesis: Stages of Oogenesis” aims to investigate the process through which female gametes are formed in the ovaries of humans. Oogenesis is a key component of sexual reproduction, involving distinct stages of development that lead to the production of a mature and functional ovum.

Procedure

• Clean the objective lens and eyepiece of the compound microscope.
• Next, take a permanent slide of the T.S. of the ovary and place it on the stage of the compound microscope.
• Observe the slide first under a lower magnification of 10X and then under a higher magnification of 40X.
• Observe and study the various stages of female gamete development.

Observation

This simulation explains the concepts of the T.S. of the ovary and the process of oogenesis. The ovary is covered by the ovarian wall, made of cuboidal germinal epithelium cells. The inner part of the ovary is the stroma, which is divided into two parts: the outer peripheral cortex and the inner medulla. The cortex consists of ovarian follicles and the medulla consists of connective tissues, blood vessels, and nerves. 

Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary. These cells start division, enter prophase-I of the meiotic division, and get temporarily arrested at that stage. They are called primary oocytes.

Each primary oocyte is surrounded by a layer of granulosa cells and is called the primary follicle. The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles, which soon transform into a tertiary follicle with a fluid-filled cavity called the antrum. The theca layer is organised into theca interna and theca external.

Now, the primary oocyte within the tertiary follicle completes its first meiotic division, forming a haploid secondary oocyte and a first polar body. The tertiary follicle further changes into the graafian follicle. The secondary oocyte develops a membrane called the zona pellucida around it. The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary through a process called ovulation. 

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