Oogenesis

• Oogenesis is the formation of egg cells or ova
• The singular of ova is ovum
• Oogenesis takes place in numerous round structures called follicles in the ovaries
• The diploid primary oocyte undergoes two successive meiotic divisions and develops into a haploid ovum or egg
• Oogenesis is completed only when the secondary oocyte is fertilized upon entering the oviduct, where meiosis II takes place upon stimulation by the sperm
• When a follicle matures, its walls rupture, setting the ovum free; this is the process of ovulation
• It takes about 28 days for a follicle to reach maturity
• Ordinarily, only one follicle matures at a time
• Ovulation may take place alternately in both ovaries
• Ovulation may also take place in succession in the same ovary
• Following the release of the ovum, the wall of the follicle collapses
• The cells of the ruptured follicle undergo changes and form a yellow mass of cells called corpus luteum
• The corpus luteum secretes a hormone that is responsible for maintaining the lining of the uterus during pregnancy
• Breaking down of the uterus lining which is discharged as menstrual flow; the process is known as menstruation.