As Spermiogenesis The transformation phase of the spermatids created by spermatogenesis into mature and fertile sperm is called. During spermiogenesis, the spermatids lose a large part of their cytoplasm and the flagellum forms, which is used for active locomotion. On the head with the nuclear DNA, opposite the point of attachment of the flagella, the acrosome forms, which contains enzymes that enable it to penetrate the egg cell.
What is spermogenesis?
In contrast to spermatogenesis, in the course of which the germ cells each go through a mitosis and a meiosis I and II and are then referred to as spermatids, spermatogenesis only affects the conversion of the spermatids into mature and fertile sperm.
Spermiogenesis of a spermatid takes about 24 days. The spermatids, which only have one set of haploid chromosomes due to the previous meiosis, are converted into a specialized cell that serves the sole purpose of penetrating a fertile female egg.
The transformation of a spermatid into a sperm is associated with serious internal and external changes. The spermatid loses almost all of its cytoplasm, so that essentially only the nucleus, which contains the DNA, remains. The greatly reduced cell is converted into the head of the future sperm. Where the centriole is located, there is a flagellum, also called the tail, which is used to actively move the sperm.
On the side opposite the flagellum, a cap forms, the acrosome, which contains enzymes that allow it to penetrate the female egg. The mitochondria, which, including their mitochondrial DNA and RNA, were originally located in the cytosol of the spermatid, attach to the central part of the flagellum and provide the necessary energy for locomotion.
Function & task
The spermatid, which is still recognizable as a haploid cell at the beginning of spermiogenesis, transforms into an externally and internally strongly changed sperm. The haploid chromosome set is no longer changed. The mitochondria are simply relocated together with the mitochondrial DNA and RNA in order to give the flagella the necessary energy for their movements. The only genetic difference between the sperm within an ejaculate is that 50 percent contain an X chromosome and the other 50 percent contain a Y chromosome.
A special feature is that the sperm sheds the flagellum when it penetrates the female egg and thus the mitochondrial DNA from the male sperm cell no longer plays a role. The mitochondrial DNA of the fertilized egg, later the zygote, comes exclusively from the mother's mitochondria.
Spermiogenesis is used to convert the spermatids into dedicated, optimized sperm cells. Strong sperm, which can move as quickly as possible towards the fertilizable egg after ejaculation, have the greatest chance of passing on their chromosome set.
After docking with the egg's membrane, a physiological process is triggered that prevents further sperm from docking. The ability to move and the energy reserves of the individual sperm can make a decisive contribution to "winning the race".
It is less about the competition between the genetically identical sperm cells within an ejaculate, but more about competition with sperm from a “foreign” ejaculate, since people do not generally live monogamous. The possibilities to win the competition against "foreign sperm" are not exhausted in "purely sporting competition", but a part of the sperm within an ejaculate are unable to move and can virtually block the path of foreign sperm. Inside an ejaculate there are also “killer sperm”, which recognize foreign sperm and can kill them with chemical agents.
Illnesses & ailments
Disorders, diseases, genetic abnormalities, excessive consumption of alcohol or other drugs and much more can lead to impaired spermiogenesis, so that reversible or permanent infertility can set in. In most cases, disorders of spermogenesis should not be viewed in isolation as they are usually the result of impaired spermatogenesis.
In principle, impaired spermiogenesis can be caused by diseases or lesions in the organs that produce sperm, the testes, or by malfunctions in hormone production. A wide variety of testicular abnormalities such as undescended testicles, testicular hypoplasia and infections of the prostate as well as mumps-related testicular inflammation (mumps orchitis) are typical causes of disorders in spermiogenesis and spermatogenesis, which usually lead to reduced fertility or even to complete infertility.
Diseases of the testes such as varicoceles, spermatoceles, hydroceles or prostate tumors can have similar effects. Radiation therapy for cancer treatment, which can damage the testes, also falls within the range of disorders of spermiogenesis by the producing organs.
Diseases that can affect spermatogenesis and spermiogenesis are considered extragenital causes. It is primarily febrile infections that can temporarily impair the formation of sperm cells as a result of an increase in temperature in the testes. Environmental toxins and work-related handling of toxic substances such as bisphenol A, organic solvents, pesticides, herbicides, heavy metals, plasticizers in plastics and much more pose risks for impaired spermiogenesis.
The hypothalamus and pituitary gland, the main control center for controlling hormonal processes in the body, also deserve special attention. If the pituitary gland is unable to provide control hormones such as FSH (follicle-stimulating hormone) and LH (luteinizing hormone) and a few others in the necessary concentration, the result is an altered - usually reduced - production of sex hormones and thus to a disruption of spermiogenesis.
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