Q--. Identify the wrong statement from the following:a. High levels of estrogen triggers the ovulatory surge.b. Orgonial cells start to proliferate and give rise to functional ova inregular cycles from puberty onwards.c. Sperms released from seminiferous tubules are poorly motile /non-motile.d. Progesterone level is high during the post ovulatory phase ofmenstrual cycle.also explain...........
Oogonia do not proliferate at puberty instead during embryonic development. It is the primary oocyte that undergo development puberty onwards. Let us study about it in details.
Oogenesis is the process of formation of ovum. It starts during embryonic growth and millions of gamete mother cells (oogonia) are formed in the foetal ovary. By the time the foetus is 25 weeks old, all the oogonia produced by female are formed by mitosis.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 characteristic fluid-filled cavity called 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 zone pellucida. The secondary oocyte receives large amount of cytoplasm and proceeds as far as the metaphase stage of meiosis II and awaits the arrival of spermatozoa for the completion of 2nd meiotic division.
Then the Graafian follicle ruptures to release the secondary oocyte (ovum) by ovulation.