Sperm – male germ cells , which is necessary for fertilization . Human Sperm consists of a head, middle section and tail ( flagellum ) , through which a male germ cell performs motion. When moving spermatozoon rotates on its axis , and the average speed is 30 inches per hour. Approximately 1-2 hours after intercourse sperm reach the fallopian tubes, where fertilization occurs .
If women limited set of germ cells ( oocytes ) is present from birth , then all men differently. At puberty ( about 12 years) boys started the development of sperm , which is under control of the hormonal system . Education of male germ cells is called spermatogenesis .
As mentioned above , spermatogenesis begins during puberty and lasts throughout the life of men . Entire life cycle of sperm ( from the beginning of its development , and before his death ) lasts an average of 90-100 days. The male gonads ( testes ) every hour is formed about 100 million sperm ! As is known , the temperature of the testicles to be 2-3 degrees below normal body temperature , so the most active process of male germ cells of the testes at a temperature passes about 34 degrees Celsius. High body temperature , tight clothing and heated seats adversely affect spermatogenesis and can significantly affect the results of semen .
Spermatogenesis takes place in three phases: the proliferation of spermatogonia , meiosis and spermatogenesis .
proliferation of spermatogonia
Spermatogonial cells ( spermatogonia or ) – this stem cells found in the membrane of tubules of the testes izvivistyh . One egg contains about one billion spermatogonia . There are three types of spermatogonial cells : dark spermatogonia A bright spermatogonia A and type B spermatogonia
Under normal conditions, the dark type A spermatogonia do not divide, and are a kind of pool of stem cells , which can be useful when a sharp decrease in the number of spermatogonia . Are continuously dividing light type A spermatogonia that through mitosis ( division ) give 2 cells . It may be two type B spermatogonial cell or one type light spermatogonia A and one type B
Type B spermatogonia undergo the stage of several divisions , eventually differentiating into spermatocytes of the first order . Recent double their number of chromosomes and are subject to stage of meiosis , which produces a 2 spermatocytes of the second order . Subsequently, a second-order spermatocytes undergo meiosis again , which leads to the formation of 4 haploid spermatids ( half ) set of chromosomes .
This final stage of spermatogenesis , which resulted in spermatids found in Sertoli cells turn into sperm. At the stage of spermatogenesis with spermatids undergoing structural changes. Originally spermatids becomes rounded, and then pulled out , it formed acrosomal granules and acrosomal cap on the head of the sperm of the future . Most of the cytoplasm of cells detached , resulting in the formation of the sperm tail .
By the time the entire spermatogenesis is approximately 64 days . Already mature sperm lives in the male about one month . In the ejaculate sperm can be stored up to 24 hours depending on external factors ( the humidity , temperature, light). In the vagina male sex cells live for several hours, and in the uterus , cervix and fallopian tubes – up to 3 days.