reproduction.txt

From Bangerter 2000
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§1: Sperm or Ovum in subject or object position
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Fertilization typically takes place in the fallopian tube between the ovary and uterus. The ovum, which develops in the ovary, is transported to the fallopian tube. The walls of the fallopian tube are covered with ciliae. The movement of these ciliae creates a current of liquid, which transports the ovum to the place of fertilization.

During fertilization, muscle contractions of the walls of the fallopian tube contribute largely to the transport of the ovum. Both the intensity of the ciliae movement and the strength of the contractions is dependent on the equilibrium between the sex hormones, oestrogen and progesterone. In this way, the ovum reaches the place of fertilization.

§2: Sperm or Ovum actively travelling or being transported
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During copulation, the semen is deposited directly in the vagina. Contractions of the female genital tract play an especially important role in transporting the spermatozoa to the place of fertilization. Here as well, ciliae in the fallopian tube cause a current which facilitates the transport of the spermatozoa.

After copulation, the spermatozoa are mainly passively transported to the place of fertilization. On the way to the fallopian tube, most of the spermatozoa die off. Even though several hundred million spermatozoa are brought into the vagina, only several thousand reach the place of fertilization.

§3: Sperm or Ovum actively travelling or being transported
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The meeting of sperm and ovum apparently takes place randomly. It is thus not the case that the spermatozoa have a sense of direction, or that the ovum somehow chemically attract the spermatozoa. The first contact takes place through an attachment reaction that is caused by substances on the surface of the egg and sperm.

One sperm must penetrate through the membrane layers into the ovum. This is made possible by a local dissolution of the membrane layers by so-called lysines, which probably come from the head of the sperm. Only then does the fusion of the ovum and sperm take place.

Immediately after the fusion of sper, and ovum, other processes take place, which lead, among other things, to a hardening of the ovum membrane. The modified membrane prevents further attachment of sperm.