Question

Explain the development of a secondary oocyte (ovum)  in a human female from the embryonic stage upto its ovulation. Name the hormones involved in this process.

Answer 1

Oogenesis

• The ovum (egg) is formed by the process of oogenesis.

• It starts during embryonic growth with millions of gamete mother cells (oogonia) forming in the foetal ovary.

• These cells undergo meiosis, but get temporarily arrested at the prophase and are called primary oocytes.

• Before reaching puberty, a large number of primary oocytes degenerate and the remaining ones get surrounded by layers of granulosa cells and new theca and are called secondary follicles.

• The secondary follicles are then converted into tertiary follicles that have a fluid-filled cavity called the antrum. At this stage, the primary oocyte present within the tertiary follicle completes meiosis, which results in the formation of haploid secondary oocyte and a tiny polar body.

• This tertiary follicle further changes into the Graafian follicle. The secondary oocyte is surrounded by the zona pellucida.

• Then the Graafian follicle ruptures to release the ovum by ovulation.