Pregnancy, its course and intrauterine development of the fetus

At sexual intercourse in the vagina of a woman, a male seminal fluid enters, in which there is a large number of male sex cells - spermatozoa. The number of spermatozoa in the seminal fluid is determined by millions, in one cubic millimeter there are 60 to 200 million. Spermatozoa have a threadlike form and consist of a head and a tail. The tail part of the spermatozoon has the ability to vibrate, which provides mobility. The speed of advancement of the spermatozoon reaches several millimeters per minute.

From the vagina, spermatozoa penetrate into the cavity of the cervix and then into the fallopian tubes. If, up to this time, an egg cell is thrown out of the ovary and enters the uterine tube, and then moves towards the uterus, then its movement and the spermatozoa will meet one another. One of the spermatozoa approaches the egg cell;on its surface a tubercle is formed, protruding towards the spermatozoon. The sperm melt the shell of the egg and penetrate into its protoplasm. This meeting usually occurs in the wide part of the pipe. The head of the spermatozoon merges with the core of the egg. The remaining spermatozoa are no longer able to penetrate the egg cell.

The process of the fusion of two male and female sex cells is called conception, or fertilization.

After the fusion of the seed and egg cells begins the process of crushing the egg. Simultaneously, the fertilized egg moves from the uterine tube to the uterine cavity, mainly due to contractions in the musculature of the tube and the ciliary movement of the hairs( cilia) located on its mucous membrane.

In the process of this advancement, a number of changes take place in the fertilized egg. By the time she gets into the uterine cavity, she becomes able to penetrate into her mucous membrane. In turn, the mucous membrane of the uterus to this period is prepared for the perception of a fertilized egg.

Once in the uterus, the egg is immersed in the thickness of the mucous membrane and, attaching to one of the walls of the uterus, gets the opportunity to get from the mother's body all that is necessary for its further development.

Introduction of the fertilized egg and the mucous membrane of the uterus( outline).

1 - the ovum, 2 - the thickened mucous membrane of the uterus, 3 - the wall of the uterus.