Of all the cells in the human body there is only one that can be seen with the naked eye. This is the ova, or oocyte that is produced by the female. They are considerably larger than the male counterpart, the sperm, or spermatozoa.
Human spermatozoa are about 55 microns long, but most of that is tail. The head measures only 5 microns. In comparison the human oocyte is roughly 100 microns in diameter, or about the same as a small grain of salt.
Female fetuses have more than 7 million potential eggs, called primary oocytes, while they are still in the womb. At birth that number drops to 1 or 2 million and by the time a woman reaches puberty only about 300,000 primary oocytes are left in her ovaries.
Roughly 300 to 400 primary oocytes mature to become eggs. If the oocyte is not fertilized within a day of leaving the ovary, it dies.
Oocytes are transported from the ovary to the uterus through the Fallopian tubes by means of tiny cilia that push them along.
While the male spermatozoa contain either X or Y chromosomes, all oocytes contain X chromosomes. This means that the male determines the sex. Both spermatozoa and oocytes have 23 chromosomes.
- Photo Credit Image by Flickr.com, courtesy of Leonardo Aguiar
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