A sperm , spermatozoon or spermatozoid (also called seminal filament or sperm cell ) is a form of gametes (germ cells), namely a mature male germ cell that is capable of independent movement and which, when united with the female germ cell, the egg cell (ovum), become the latter Fertilization leads. Sperm are usually produced by an individual in large numbers in the seminiferous tubules of the testes and are essential because they are smaller than about fertilizing the egg, as opposed to the egg no major quantities of plasma and yolk containing nutrients contained.
Male germ cells that are not able to move independently are called spermatia (singular spermatium ).
Different cell types, including spermatocytes, have a form of immune privilege .
Sperm with flagella
The human sperm is a flagellated cell that has a head part with a haploid chromosome set in a cell nucleus (either with X or Y chromosome), a middle part (“neck” with centrosome and surrounding mitochondria packages) and a flagellum (also referred to as the "tail"). The head, which is responsible for penetrating the egg cell , is on the side of the head opposite the scourge, the front side when swimming . At the front of the sperm head is the head cap ( acrosome ), which is filled with enzymes that make it easier to penetrate the egg membrane.
Special forms of sperm
In the case of lower crustaceans and a number of arachnids , the sperm can be spherical overall. The roundworm has nail-shaped sperm with a shiny body made of specific proteins . Other roundworms and mites have amoeboid motile sperm. In the decapods ( Decapoda ) a kind of "explosion device" occurs a spring mechanism in the form that propels the sperm into the ovum.
The size of the sperm varies greatly between species. While the giant sperm of ostracods (mussel crabs) are 7 mm long and can thus be up to ten times as long as the mussel crabs themselves, human sperm are only about 60 µm in length: the head is about 5 µm long and 3 µm wide, while the scourge including the “neck” is around 50 µm long. The size of the sperm can vary even within the same species , depending on whether or not a male has multiple rivals. It has been found in frogs that the size of the sperm and thus the length of the flagella increases when the male concerned has to deal with other males to fertilize the eggs of a female frog. The sperm with the longest flagella, which can swim the fastest, have the greatest chance of being the first to reach the frog eggs released by the female into the water.
Giant sperm are found not only in freshwater mussel crabs , but also in some other species in the animal kingdom. Some of these are many times longer than their producer. They are found in some types of worms, butterflies, and water bugs. The fruit fly Drosophila bifurca holds the size record . Their sperm cells measure up to 58 millimeters in length, more than ten times their body length.
Human sperm can be observed with a normal light microscope at a magnification of 100, but better 400 times, without coloring.
In Galenos (2nd century AD) the idea of male formed in the testes and female "sperm" or semen formed in the "female testes", the ovaries, still prevailed.
Spermatozoa were discovered microscopically in 1677 by the medical student Johan Ham , his teacher Antoni van Leeuwenhoek carried out further examinations. Leeuwenhoek named the newly discovered "particles" as he had previously discovered bacteria as animalcula , i.e. (seed) animals, and assigned them to the infusoria ; he already correctly recognized that they must be formed in the testes. According to his idea as one of the founders of the preformation theory, it was something like human larvae. The entire human being would therefore already be pre-formed in the sperm as “ homunculus ” and only need to grow up; he denied any significance of the mother and the maternal eggs (the egg cell was only discovered in 1827); however, his competitor Jan Swammerdam took the opposite view. In the research of the following centuries a bitter dispute raged between the "ovists", who located the germ of the future human being in the egg, and the "animal culists", who located it in the sperm. Both believed in a preformation of the human being in the respective germ, possibly even nested smaller and smaller, and thus going back to the first humans Adam or Eve.
The expression spermatozoon (Greek for seed animals) was first used in 1826 by the embryologist Karl Ernst von Baer , who rightly considered the fertile function of these "living beings in the sperm" to be unproven.
In 1842 the Swiss biologist Albert von Kölliker published his studies on sperm in the work Investigations on the meaning of the seminal threads .
The fact that sperm penetrate the ovum was first observed and reported microscopically in 1843 by Martin Barry .
Construction and function
The man's sperm is made up of
- a head part that contains the haploid set of chromosomes and between 2682 and 2886 different mRNA molecules in the cell nucleus ,
- a middle piece with a multitude of mitochondria that provide the energy in the form of ATP molecules for locomotion,
- a movable tail part with a longitudinal fibril system of microtubules for locomotion.
Human sperm serve - like the spermatozoa of other organisms - to fertilize a female egg . After their completion ( spermatogenesis ), they are initially stored in the male epididymis , from where they are expelled via the vas deferens and the urethra during ejaculation during the male orgasm . Around 300 million of them end up in the female vagina . From the vagina only a small part of the sperm, which are intended for fertilization, reaches the egg cell via the fallopian tube , the far larger part does not succeed in the obstacle-rich path to this region, or it is intended for other functions (see sperm competition ).
On the way to the egg cell, the sperm are likely chemotactically guided by progesterone or scent-like substances, the pH value and temperature differences. The stimuli are picked up on the one hand by molecules of the large family of G-protein-coupled receptors in the membrane of the initial part of the sperm tail. Some are identical to those in the olfactory cells of our nose (olfactory receptors), on the other hand through the CatSper ion channel, which can also be activated by many low-molecular substances. Experimentally it could be shown: If the fragrance bourgeonal (lily of the valley fragrance) binds to the OR1D2 , the calcium concentration rises inside the sperm . According to current knowledge, the same applies to binding and activating the CatSper channel. As a result, the sperm changes its swimming direction and at the same time doubles its swimming speed. The changes in calcium concentrations, not their absolute levels, are responsible for the direction of movement. However, it is highly unlikely that the natural binding partner of the Bourgeonal receptor is the only “guide” to the egg cell; rather, several factors can be assumed.
Because of the many obstacles, under normal conditions only about 300 sperm reach the point at the end of the fallopian tube where the egg cell is waiting to be fertilized. However, the egg can only be fertilized by a single sperm. During fertilization , the contents of the sperm head penetrate the egg cell, which becomes diploid and is now called a zygote . According to recent findings, the male mRNA molecules that have penetrated the egg cell together with the nucleus of the sperm cell influence the development of the embryo emerging from the zygote .
Human sperm have a mobile flagellum . In the 17th century, the Dutch naturalist Antoni van Leeuwenhoek was the first to describe human sperm cells and, under the light microscope, also recognized the elongated flagella with which they move. According to this researcher, when sperm swim, they whip their flagella in a snake-like fashion like eels in water. That is why it has been in textbooks for over 300 years that the two points marked on the flagellum move up (left point) and down (right point). This speed is divided into the part that runs parallel (V [par]) to the section of the flagellum and the part that runs perpendicular (V [perpendicular]) to it. The resulting force F is in turn divided into two parts, namely the part of the force that acts parallel to the direction of movement of the sperm (F [horiz]) and the part that acts vertically to the direction of movement (F [vert]). The sum of the two forces, which are directed parallel to the direction of movement of the sperm, form the driving force. However, according to a new study, when moving, the flagella always rotate in one direction, more like a corkscrew . The research team led by Hermes Gadêlha has now made high-resolution 3-D images of sperm and were able to observe the actual type of movement. Accordingly, the scourge is crooked and only snakes to one side. In order not only to move around in a circle and thus miss the path to the egg cell, the sperm rotate as a whole like a corkscrew or top , compensate for the one-sided whipping movement of the flagellum, and move forward. With the normal microscope used by van Leeuwenhoek and still often used today, this was not and is not recognizable, because the fast and synchronized rotary movements look as if the tail were moving symmetrically from side to side. According to the researchers, the new findings from observations with the 3-D microscope can also have practical consequences. With more than half of all cases of infertility in men, it is very important and fundamental to understand exactly how the tail of sperm actually moves and functions in order to identify unhealthy specimens in the future.
After a maturation period of around 10 weeks from spermatogony to spermatozoa (mature sperm), a sperm can survive in the man's sperm depot for up to a month. Depending on the environmental conditions (light, temperature, humidity), sperm can survive in the air for up to 24 hours. As soon as the ejaculate with the sperm dries, they die. So there can be no fertilization by means of dried sperm. This is because sperm need the fluid that surrounds them to survive: seminal plasma. As long as the sperm cells' ability to move is ensured, they are viable. By balancing the pH values of the vagina (pH 4–5) and cervical mucus and sperm (pH 6–8), it is possible for the sperm to survive in what is in itself a "hostile" environment. Under optimal conditions in the bays of the cervical mucosa, sperm can survive there for up to seven days. Of the average 250 million sperm per ejaculation, only about 500 to 800 reach the fallopian tubes. One reason for this is the cervical mucus, through which the non-buoyant sperm are filtered. A deviation from the optimal, slightly basic pH value (7.2–7.8) leads to the death of the sperm. Most spermicides used in mechanical and chemical contraception methods work on this basis. The pH-neutral care products often used in the genital area are not spermicidal and are unsuitable for contraceptive aftercare.
The sperm quality in industrialized countries has been declining worldwide for years. In 60% of the examined Swiss between 18 and 22 years of age, at least one parameter is below the limit value of the World Health Organization (WHO) for good fertility.
The term sperm competition describes the competition of sperm from one or more males for the chance to fertilize an egg cell . Sperm competition arises because the males of all animal species much more sperm than females produce its kind capable of fertilization oocytes.
Another variant, which was first observed in insects and is also said to occur in mammals, is that the males not only ejaculate fertilizable sperm, but also immobile sperm and those that kill sperm that compete with cell surface molecules. The immobile sperm block the path of any foreign sperm, so that it is more difficult for them to migrate along the female mucosal surfaces to the egg cell. So-called "killer sperm" look specifically for foreign sperm whose surface structure does not correspond to your own, and kill them chemically.
A defensive strategy is to mate a female as often as possible. As a result, there is always a greater amount of her own sperm in the female's body. This means that a competitor's sperm are less likely to be fertilized.
Use of the term "seeds"
Sperm and semen are often referred to as semen . This can be misleading, because a seed is an organ of dissemination (often embedded in the pulp) of the higher plants, which consists of a dormant plant embryo surrounded by nutrient tissue and a seed coat.
The use of the term seed or semen for the sperm is derived from the Bible , where it does not claim to be scientifically correct, but rather emphasizes kinship, and this in a way that was understandable for the circumstances at the time. The Hebrew word for seed ( זרע zera ) is used there indiscriminately for plants, animals and humans. So on the one hand the woman receives the male seed (Num 5, 28) or wakes him up during erotic play (Gen 19, 32 and 34), on the other hand the land is sown with the seeds of the field crops (Deut 29, 22; Ez 36, 9) .
In addition, in ancient and medieval ideas, the presence of a “seed” as a germ cell was not limited to the male sex.
From ancient Egypt comes the wrong notion that the male seed is already the human being in nuce , who only needs to mature in the womb, as it were in a nutrient solution. Finally, the term seed also stands for the offspring themselves. When the Bible speaks of the seed of Abraham , it means the offspring that emerged from Abraham (Isa. 41: 8; Jer. 33, 26). All of these meanings are not meant here. Newer school books no longer speak of the sperm duct , but explicitly of the sperm duct .
In fact, the Greek word σπέρμα (sperm) means nothing other than "semen". This can also be found in botanical names such as angiosperms for "bedecktsamer". So the ambiguity exists in several languages.
More word formations
- Spermatophores (packets of seeds) are used to transmit sperm in some animal species.
- A spermiogram is created by analyzing the ejaculate and is used to assess the man's fertility.
Popular science books
- Britta Hähnel: ReproTier-Kompetenzverbund presents: The small sperm primer : Size measurement on sperm from different animal species . carried out and documented in the Institute for Reproduction of Agricultural Animals Schönow eV, Mensch & Buch, Hähnel 2007, ISBN 978-3-86664-186-0 .
- Robie H. Harris: What comes next is ... just crazy! A book about eggs and sperm, childbirth, babies and living together . Beltz & Gelberg, Weinheim 2002. ISBN 3-407-75319-5 .
- Vivien Marx: The semen book, everything about sperm, sex and fertility (= Fischer-Taschenbuch. Volume 14140). Fischer, Frankfurt am Main 1999, ISBN 3-596-14140-0 .
Special scientific literature
- 1938: Walther Schönfeld : About the discovery of human seminal threads (Ludwig von Hammen from Danzig - Johan Ham from Arnheim [Holland] - Antony van Leeuwenhoek from Delft). In: Archives for Dermatology and Syphilis . Volume 178, Number 3, 1938, pp. 358-372, .
- 1950: Olaf W. Dietz: The number of sperm in the ejaculate of the billy goat in relation to the sexual pause . Dissertation University of Leipzig, Faculty of Veterinary Medicine, December 15, 1950, .
- 1971: Charles A. Joël: Historical survey of research on spermatozoa from antiquity to the present. In: Fertility disturbances in men and women. Basel 1971, pp. 3–43.
- 1974: Stephan Schulte-Wrede: Scanning electron microscopy of sperm from the domestic sheep "Ovis ammon aries L." Dissertation University of Munich 1974, (From: Journal for Cell Research and Microscopic Anatomy , No. 134, 1972, , p 105–127, together with Rudolf Wetzstein).
- 1983: Ulrich Wirth: Sperm and spermatogenesis in nematodes and the importance of sperm for the phylogenetics of the metazoa . Dissertation University of Freiburg im Breisgau 1983, .
- 1990: Heike Rauhaus: Investigations into the morphology and live-dead coloration of sperm from some domestic animals . Dissertation University of Munich 1990, .
- 1995: Dirk Schulze Bertelsbeck: The importance of sperm antibodies in serum and on sperm for the diagnosis of immunologically induced infertility . Dissertation University of Münster (Westphalia) 1995, .
- 1996: Manuela Quandt: Inhibition and stimulation of sperm migration in the in vitro sperm-mucus interaction model. Dissertation University of Heidelberg 1996, .
- 1996: Stefan Hans Uhlich: Comparison of sperm after preparation with glass wool filtration or Percoll density gradient centrifugation: an electron microscopic examination . Dissertation University of Ulm 1996, .
- 1999: World Health Organization (ed.): WHO Laboratory Manual for the Examination of Human Ejaculate and Sperm-Cervical Mucus Interaction (Original title: WHO Laboratory Manual for the Examination of Human Semen and Sperm Cervical Mucus Interaction , translated by Eberhard Nieschlag and Susan Nieschlag in collaboration with Monika Bals-Pratsch). Springer, Berlin / Heidelberg / New York et al. 1999, ISBN 3-540-66335-5 .
- 2001: Andrea Wagner: The functional sperm reservoir in mammals. Characterization of the carbohydrate-mediated processes of sperm-oviduct binding in pigs . Dissertation at the University of Veterinary Medicine Hannover 2001, online PDF, free of charge, 113 pages, 1.3 MB). (
- 2002: Brigitte Reimesch: Studies on the influence of coenzyme Q10 and a mixture of coenzyme Q10 and vitamin C, in vitro, on the mobility of sperm ( microfiche ). Dissertation University Erlangen-Nuremberg 2002, .
- 2002: Steffen Klaus Meurer: Molecular biological and immunological characterization of chemoreceptors in mammalian sperm (= reports from Forschungszentrum Jülich ). Research Center Jülich, Central Library, Jülich 2002 (Dissertation University of Cologne 2002).
- 2003: Johannes Solzin: Chemotaxis of sea urchin sperm, kinetic measurements of intracellular messenger substances (= Jülich Research Center: Reports of the Jülich Research Center , Volume 4030). Dissertation University of Cologne 2003, .
- 2010: Britta Verena Behr: The biotechnological potential for manipulating offspring sex in the rhinoceros and the elephant , Freie Universität, Berlin 2010, ISBN 978-3-86664-702-2 (Dissertation FU Berlin 2009, journal number 3291 online PDF, free of charge, 126 Pages, 3.8 MB (English)).
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