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How does human reproduce?
Humans reproduce sexually when two cells (gametes), an egg (ovum) and a sperm, come together. Each gamete contributes half of the genetic material contained in the foetus. The hormones which control the production of sperm and eggs are called gonadotrophins. There are two types of gonadotrophins: Follicle Stimulating Hormones (FSH) and Luteinizing Hormone (LH). These two hormones are produced in a tiny, pea-size gland at the base of the brain called the pituitary gland. In men, they stimulate the testicles to produce sperm and testosterone. In women they act on the ovaries, where the eggs develop, producing the female sex hormones oestrogen and progesterone.

The mature egg survives only 24-48 hours, while sperm remain viable longer. In natural conception sperm is placed inside the vagina at the time of intercourse. The mucus in the cervix (the neck of the uterus) is slippery around the time of ovulation, which enables the sperm to swim into the uterus. The uterus then contracts in such a way as to help the sperm move up into the fallopian tube to reach the egg.

Once a sperm has penetrated the shell surrounding the egg (zona pellucida) it sets up a barrier stopping other sperm from penetrating. When the head of the sperm has released its contents into the egg, the egg is fertilised. The egg then starts to divide and becomes an embryo. Few days after fertilisation the embryo implants in the endometrium and starts to produce Human Chorionic Gonadotrophins (HCG), the hormone that causes a "Positive" pregnancy test.


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