explain the steps in the formation of an ovum from an Ooganium in humans
Answers
Oogenesis is initiated in embryonic ovaries of the female fetus.
The cell starts division (oogonia) and enter into prophase 1 of the meiotic cycle and get temporarily arrested at that stage, called primary oocyte.
Each primary oocyte gets surrounded by a layer of granulosa cell and then called primary follicle. Many of these degenerate, hence by puberty only 60000 - 80000 primary follicle remain.
Further, it gets surrounded by more layers of granulosa and a new theca and form secondary follicle.
Soon these transform into the tertiary follicle, characterized by the presence of fluid-filled cavity called Antrum. At this stage, the primary oocyte grows and completes it's first meiotic division.
The division is unequal and leads to the formation of a large secondary oocyte and a tiny polar body.
The tertiary follicle further mature into Graafian follicle, the secondary oocyte forms a new layer called Zona pellucida surrounding itself.
During ovulation, this follicle ruptures to release secondary oocyte/ovum (which completes 2nd meiotic division just prior to fertilization)