The term sperm is derived from the Greek word (σπέρμα) "sperma" (meaning "seed") and refers to the male reproductive cells. In the types of
sexual reproductionknown as anisogamyand oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. The humansperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploidcell. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, whereas a non-motile sperm cell is referred to as a spermatium. Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a totipotent zygoteis formed with the potential to develop into a new organism. Mammalian sperm cells can live for up to 3 days inside the female reproductive system.fact|date=April 2008The spermatozoa of animals are produced through spermatogenesisinside the male gonads ( testicles) via meiotic division. Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) via mitotic division. In flowering plants, sperm nuclei are produced inside pollen.
The sperm cell consists of a head, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an
acrosome, which contains enzymes used for penetrating the female egg. The midpiece has a central filamentous core with many mitochondria spiralled around it, used for ATPproduction for the journey through the female cervix, uterusand uterine tubes. The tail or " flagellum" executes the lashing movements that propel the spermatocyte.
Motile sperm cells
Motile sperm cells typically move via flagella and require water in order to swim toward the egg for fertilization. The uniflagellated sperm cells (with one flagellum) produced in most
animals are referred to as spermatozoa, and are known to vary in size.
Motile sperm are also produced by many
protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes, they are multi-flagellated (carrying more than one flagellum).
nematodes, the sperm cells are amoeboidand crawl, rather than swim, towards the egg cell.cite journal |author=Bottino D, Mogilner A, Roberts T, Stewart M, Oster G |title=How nematode sperm crawl |journal=J. Cell. Sci. |volume=115 |issue=Pt 2 |pages=367–84 |year=2002 |pmid=11839788 |doi=]
In order to move towards the ova the sperm swim through the womans vaginal juices coating the walls of the womb and cervix.
Non-motile sperm cells
Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in a spermatangium.
Because spermatia cannot swim,they depend on their environment to carry them to the egg cell. Some
red algae, such as " Polysiphonia", produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphaefor fertilization in a mechanism similar to insect pollinationin flowering plants.cite book | last = Sumbali| first = Geeta | coauthors = | title = The Fungi | publisher = Alpha Science Int'l Ltd. | date = 2005 | location = | pages = | isbn = 1842651536]
Fungal spermatia (also called pycnidiospores) may be confused with conidia. Conidia are
spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as " Neurospora crassa", spermatia are identical with microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.cite journal |author=Maheshwari R |title=Microconidia of Neurospora crassa |journal=Fungal Genet. Biol. |volume=26 |issue=1 |pages=1–18 |year=1999 |pmid=10072316 |doi=10.1006/fgbi.1998.1103]
land plants, including most gymnosperms and all angiosperms, the male gametophytes (pollen grains) are the primary mode of dispersal, for example via wind or insect pollination, eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma of a receptive flower, it germinates and starts growing a pollen tubethrough the carpel. Before the tube reaches the ovule, the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei which are then discharged through the tube into the ovulefor fertilization.
protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridiumsurrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.
A study by the
University of Californiahas suggested that folatemay protect sperm cells from aneuploidy. [http://news.bbc.co.uk/2/hi/health/7303375.stm]
On the global market,
Denmarkhas a well developed system of sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple. [http://www.ncbio.org/NcBioBurrell.pdf Assisted Reproduction in the Nordic Countries] ncbio.org ] Furthermore, Nordic sperm donors tend to be tall and highly educated [http://www.newser.com/story/34788/fda-rules-block-import-of-prized-danish-sperm.html FDA Rules Block Import of Prized Danish Sperm] Posted Aug 13, 08 7:37 AM CDT in World, Science & Health] and have altruistic motives for their donations, partly due to the relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay, Canada, Kenya, and Hong Kong. However, the Food and Drug Administration(FDA) of the US has banned import of any sperm, motivated by a risk of mad cow disease, although such a risk is insignificant, since artificial insemination is very different from the route of transmission of mad cow disease. [http://www.laweekly.com/news/news/the-god-of-sperm/17290/ The God of Sperm] By Steven Kotler] The prevalence of mad cow disease is one in a million, probably less for donors. If prevalence was the case, the infectious proteins would then have to cross the blood-testis barrierand the sperm would have to be swallowed orally to make transmission possible.
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