In girls of approximately 10-12 years, hormones of the anterior pituitary gland stimulate the development of ovaries. They produce female sex hormones, resulting in increased mammary glands, skeletal growth and body hair on the female type. At this time, the eggs begin to Mature and the first menstruation appears. She is a manifestation of the fact that a girl has become a girl. And although the egg can already be fertilized, but the body of a very young girl is not yet ready for full-fledged gestation of the fetus.

 

      The process of maturation of eggs has a cyclic nature and is called the menstrual cycle . Its duration is 24-30 (most often 28) days. Approximately in the middle of the cycle, ovulation occurs, that is, the output of the egg from the follicles. In place of the burst follicle, a yellow body is formed. It is a temporary gland of internal secretion that produces the pregnancy hormone (progesterone). Its function is to delay the maturation of other follicles, prepare the uterus to accept a fertilized egg (the thickness of its mucous membrane increases, it sprouts a large number of vessels filled with blood).