The sperm path, in humans and animals, is the short but complex story of the beginnings of life. Beyond the basics of mating, creation, and conception, scientists have closely studied the exact means of sperm transport to facilitate artificial insemination, infertility treatment, and contraception. This includes not only an understanding of what happens to the sperm before it leaves the man, but also after it enters the woman.
The common knowledge is that sperm transport begins when sperm cells are produced in the male testes, but that is the scope of knowledge for many people. In each of the testicles, small coils called siminiferous tubules make approximately 12,000,000,000 sperm cells each month in the average mature man. Before maturity, these cells are stored just above the tubules in the epididymis, where they remain until maturity.
When the penis is stimulated, the sperm transport moves from the epididymis, through the vas deferens tube to the ejaculatory ducts. At this point, the cells unite with seminal fluid produced in nearby seminal vesicles. This liquid contains food for the cells in the form of glucose and protection against the acidic climate of the vagina in the form of alkalines. Upon ejaculation, seminal fluid is propelled through the prostate gland, adding a thick milky prostate fluid to increase speed by swimming through the urethra to propel it into the vagina.
Sperm transport can last up to 48 hours. That is the time that the sperm have to find and fertilize the egg inside the uterus before perishing. According to the University of Pennsylvania School of Medicine, only about 200 of the roughly 300,000,000 sperm in each ejaculation will reach the egg. Only one, and occasionally a few more, will have access to start a new life.
Once deposited at the cervical entrance, the seminal fluid will begin to release the sperm cells from its grip. This starts the training process, or final maturation and hyperarousal. The cells mix with acidic cervical mucus, which removes weak cells and allows strong cells to enter the cervix.
When sperm transport reaches the fallopian tubes, the uterus actually stores thousands of sperm cells in suspended fertility until the egg reaches the midsection of the fallopian tubes, called the ampullary-isthmic junction. This is where most of human fertilization takes place, as sperm, induced by hormonal and thermal impulses, can reach the egg or immature ovum. Here, the outer membrane of the egg, called the zona pellucida, allows one sperm to enter and then blocks all the others. A single-celled zygote forms between the egg and the sperm, which in the next nine months will divide several times to produce offspring.