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Reproductive processes in men

The male body produces millions of sperm cells every day that can fertilize a female egg. Those who are well informed about these processes can increase the chances of getting pregnant or protect themselves better against an unwanted pregnancy.

At the onset of puberty, the men’s pituitary gland produces hormones that control the function of the testicles. Hormones are messenger substances that are formed in the body's glands and released into the blood. They are not only important for fertility and sexuality, in addition to many other bodily functions, they also influence the immune system and mental well-being.

The so-called follicle-stimulating hormone (FSH) regulates the formation of sperm cells in the testes. The luteinizing hormone (LH) controls the production of the sex hormone testosterone. The formation and release of and are dependent on the gonadotropin-releasing hormone (GnRH), which is formed in the diencephalon (hypothalamus). The release of this so-called release hormone is regulated by the cerebral cortex.

External stimuli and emotional signals that are processed in the brain also have an effect on the hormonal control system and can have a positive or negative effect on the production of sperm cells.

The formation of sperm cells (spermiogenesis)

Sperm develop in the seminiferous tubules of the testicles. From there they go to the epididymis. There the sperm cells finally mature. Sperm measure around 0.06 mm and are among the smallest cells in the body. Every single sperm contains the man's entire genetic make-up.

The entire development and maturation process of the sperm takes about three months. A constant body temperature of around 35 degrees Celsius is required for sperm formation. To ensure this, the testicles draw closer to the (warm) body at low temperatures. At higher temperatures, the skin of the scrotum expands so that the testicles hang a little lower. This means that they are further away from the body and can “cool down” better.

The mature sperm cells are stored in both the epididymis and the vas deferens. They cannot yet move on their own, but are transported to the prostate by contractions of the spermatic ducts.

During an orgasm, not only the prostate but also the vas deferens contract strongly, causing ejaculation. The sperm get into the urethra and out through the penis. If there is no ejaculation for a long time, the sperm are broken down again by the body's immune cells or transported outside through an involuntary ejaculation (usually during sleep).

The seminal fluid (semen)

When a man orgasms, 2 to 6 milliliters of semen (ejaculate) are generally expelled from the urethra. It serves as a means of transporting the sperm to the egg cell and has a transparent, milky appearance. In every milliliter of ejaculate in a fertile man there are on average between 20 and 60 million sperm cells. Forty to a few hundred million sperm leave the body with each ejaculation.

The sperm cells themselves only make up about five percent of the amount in the sperm. Before ejaculation they mix with secretions from other glands, especially the prostate and the vesicle glands. These secretions are very important for the fertilization ability of the sperm cells. Among other things, they ensure the mobility of the sperm cells and provide them with energy.

The sperm of a man who wants to father a child should contain at least 15 million sperm per milliliter, because not all of them are capable of fertilization. Often around half of them are not fully developed and not sufficiently mobile. This and some obstacles on the way to the egg cell mean that in the end only a few hundred sperm cells reach their destination.

After ejaculation

Immediately after the ejaculation, the sperm are still immovably enclosed in the viscous seminal fluid. After 15 to 30 minutes, the secretion of the prostate causes the sperm to liquefy significantly and the sperm to move towards the fallopian tubes. It takes one to three hours to travel 12 to 15 centimeters through the uterus into the fallopian tubes. The uterus supports them with targeted but imperceptible muscle contractions. In this way, however, immune cells in the uterus attack the (foreign) sperm cells, so that only a few hundred of the original millions get into the correct fallopian tube and the egg.

The egg and sperm are brought together by the movement of fine cilia and contractions of the fallopian tube. The sperm now jointly dissolve the outer shell of the egg, but only one sperm finally succeeds in penetrating the inside of the egg and fertilizing it. As soon as this has happened, a mechanism is triggered in the egg cell that makes fertilization by further sperm impossible. The female body breaks down the remaining sperm cells.

The fertilized egg cell eventually migrates down the fallopian tube and nests in the lining of the uterus to develop further.