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People have sex for pleasure, reproduction, or both. Pregnancy happens when an egg and sperm successfully meet through intercourse or in vitro fertilization. What do they look like, and how many do we all have?
This page has been archived and is no longer updated. Published online 25 March Nature doi Claire Ainsworth.
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Achieving a healthy pregnancy is a complicated, multi-stage process involving two people. Every month, the female ovulates one mature egg from one of her ovaries. Here, it will begin to move slowly down the tube towards the womb uterus.
Fig 1. The journey begins with millions of sperm cells that are released into the female reproductive tract during intercourse. The sperm cells gain their full ability to swim when they are ejaculated into the reproductive tract [ 1 ],[ 2 ].
To become pregnantsperm from a male has to meet an egg from a female. This can happen when a male and female have sexual intercourse, when the penis is in the vagina. If an egg has been released and is in the fallopian tube, one of these sperm may reach the membrane of the egg and get inside it.
The cytoplasm of the sperm contains NOS, which is activated along with the acrosome reaction by contact with egg jelly yellow ; above, the NOS turns green when activated and produces NO light green spray. Upon fusion with the egg, NOS is released into the egg, whereby the NO produced activates calcium release red spray. Calcium activates NOS already present in the egg, releasing more NO, which releases more calcium, and so on.
While you release only a single egg each month, your partner releases millions of sperm in a single ejaculation — all with their eye on that single prize. But only one of those sperm will be crowned the victor, and the odds are stacked against fertilization. Luckily, egg and sperm have developed some pretty nifty tricks to give themselves a fighting chance.
Fertilizationunion of a spermatozoal nucleusof paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo. In all organisms the essence of fertilization is, in fact, the fusion of the hereditary material of two different sex cellsor gameteseach of which carries half the number of chromosomes typical of the species. The most primitive form of fertilization, found in microorganisms and protozoans, consists of an exchange of genetic material between two cells.