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sperm
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{{Other uses}}{{pp-semi-indef|small=yes}}(File:Complete diagram of a human spermatozoa en.svg|thumb|right|350px|Diagram of a human sperm cell)Sperm is the male reproductive cell. In the types of sexual reproduction known as anisogamy and its subtype oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. 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 new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell. In mammals, sperm develops in the testicles, is stored in the epididymis, and released from the penis.The word "sperm" is derived from the Greek word (σπέρμα) sperma (meaning "seed"). (File:Human sperm under microscope.webm|thumb|Video of human sperm cells under a microscope.)

Sperm in animals

{{Further|Spermatozoon}}

Function

The main sperm function is to reach the ovum and fuse with it to deliver two sub-cellular structures: (i) the male pronucleus that contains the genetic material and (ii) the centrioles that are structures that help organize the microtubule cytoskeleton.

Anatomy

(File:Sperm-egg.jpg|thumb|right|200px|Sperm and egg fusing)The mammalian sperm cell can be divided in 2 parts:
  • head: contains the nucleus with densely coiled chromatin fibers, surrounded anteriorly by a thin, flattened sac called the acrosome, which contains enzymes used for penetrating the female egg. It also contains vacuoles.JOURNAL, 4346294, 25780567, 10.1186/2051-4190-23-3, 23, The nature of human sperm head vacuoles: a systematic literature review, 2013, Basic Clin Androl, 3, Boitrelle, F, Guthauser, B, Alter, L, Bailly, M, Wainer, R, Vialard, F, Albert, M, Selva, J,
  • tail: also called the flagellum, is the longest part and capable of wave-like motion that propels sperm for swimming and aids in the penetration of the egg. Sperm motility depends on the 4 parts of the tail: connecting piece, midpiece, principal piece, and the end piece.Fawcett, D. W. (1981) Sperm Flagellum. In: The Cell. D. W. Fawcett. Philadelphia, W. B. Saunders Company. 14: pp. 604-640.Lehti, M. S. and A. Sironen (2017). "Formation and function of sperm tail structures in association with sperm motility defects." Bi
The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole like.JOURNAL, 10.1038/s41467-018-04678-8, 29880810, 5992222, A novel atypical sperm centriole is functional during human fertilization, Nature Communications, 9, 1, 2210, 2018, Fishman, Emily L, Jo, Kyoung, Nguyen, Quynh P. H, Kong, Dong, Royfman, Rachel, Cekic, Anthony R, Khanal, Sushil, Miller, Ann L, Simerly, Calvin, Schatten, Gerald, Loncarek, Jadranka, Mennella, Vito, Avidor-Reiss, Tomer, JOURNAL, 10.1534/genetics.109.101709, 19293139, 2674812, A Proximal Centriole-Like Structure is Present in Drosophila Spermatids and Can Serve as a Model to Study Centriole Duplication, Genetics, 182, 1, 133–44, 2009, Blachon, S, Cai, X, Roberts, K. A, Yang, K, Polyanovsky, A, Church, A, Avidor-Reiss, T, The midpiece has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus and uterine tubes.The tail or "flagellum"executes the lashing movements that propel the spermatocyte.JOURNAL, Ishijima, Sumio, Oshio, Shigeru, Mohri, Hideo, 1986, Flagellar movement of human spermatozoa, Gamete Research, 13, 3, 185–197, 10.1002/mrd.1120130302, During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centriole, which is responsible for forming the centrosome and microtubule system.BOOK, The biology of fertilization in humans, Patrizio, Pasquale, A color atlas for human assisted reproduction: laboratory and clinical insights, Lippincott Williams & Wilkins, 2003, 978-0-7817-3769-2, 3,weblink Hewitson, Laura, Schatten, Gerald P., yes, 2013-11-09, etal,

Origin

The spermatozoa of animals are produced through spermatogenesis inside the male gonads (testicles) via meiotic division. The initial spermatozoon process takes around 70 days to complete. In the spermatid stage, the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan.Semen and sperm qualitySperm cells are carried out of the male body in a fluid known as semen. Human sperm cells can survive within the female reproductive tract for more than 5 days post coitus.JOURNAL, Gould, JE, Overstreet, JW, Hanson, FW, 1984, Assessment of human sperm function after recovery from the female reproductive tract, Biology of Reproduction, 31, 5, 888–894, 10.1095/biolreprod31.5.888, 6518230, Semen is produced in the seminal vesicles, prostate gland and urethral glands.In 2016 scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids artificially from stem cells. They injected these spermatids into mouse eggs and produced pups.JOURNAL, 10.1038/nature.2016.19453, Researchers claim to have made artificial mouse sperm in a dish, Nature, 2016, Cyranoski, David,

Sperm quality

(File:Sperm stained.JPG|thumb|left|200px|Human sperm stained for semen quality testing.)Sperm quantity and quality are the main parameters in semen quality, which is a measure of the ability of semen to accomplish fertilization. Thus, in humans, it is a measure of fertility in a man. The genetic quality of sperm, as well as its volume and motility, all typically decrease with age.WEB,weblink Does Age Affect Male Fertility?, Gurevich, Rachel, 2008-06-10, About.com, 14 February 2010, (See paternal age effect.)DNA damages present in sperm cells in the period after meiosis but before fertilization may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo. Human sperm cells are particularly vulnerable to free radical attack and the generation of oxidative DNA damage.JOURNAL, Gavriliouk D, Aitken RJ, Damage to Sperm DNA Mediated by Reactive Oxygen Species: Its Impact on Human Reproduction and the Health Trajectory of Offspring, 868, 23–47, 2015, 26178844, 10.1007/978-3-319-18881-2_2, Advances in Experimental Medicine and Biology, 978-3-319-18880-5, (see e.g. 8-Oxo-2'-deoxyguanosine)The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage.JOURNAL, Marchetti F, Wyrobek AJ, DNA repair decline during mouse spermiogenesis results in the accumulation of heritable DNA damage, DNA Repair, 7, 4, 572–81, 2008, 18282746, 10.1016/j.dnarep.2007.12.011,weblink Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in the fertilizing sperm cells, and disruption of maternal DNA double-strand break repair pathways increases sperm cell-derived chromosomal aberrations.JOURNAL, Marchetti F, Essers J, Kanaar R, Wyrobek AJ, Disruption of maternal DNA repair increases sperm-derived chromosomal aberrations, Proceedings of the National Academy of Sciences of the United States of America, 104, 45, 17725–9, 2007, 17978187, 2077046, 10.1073/pnas.0705257104, Treatment of male mice with melphalan, a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress though DNA repair-competent phases of spermatogenic development.JOURNAL, Marchetti F, Bishop J, Gingerich J, Wyrobek AJ, Meiotic interstrand DNA damage escapes paternal repair and causes chromosomal aberrations in the zygote by maternal misrepair, Scientific Reports, 5, 7689, 2015, 25567288, 4286742, 10.1038/srep07689, Such unrepaired DNA damages in sperm cells, after fertilization, can lead to offspring with various abnormalities.

Sperm size

Related to sperm quality is sperm size, at least in some animals. For instance, the sperm of some species of fruit fly (Drosophila) are up to 5.8 cm long — about 20 times as long as the fly itself. Longer sperm cells are better than their shorter counterparts at displacing competitors from the female’s seminal receptacle. The benefit to females is that only healthy males carry ‘good’ genes that can produce long sperm in sufficient quantities to outcompete their competitors.JOURNAL, 10.1038/nature18005, 27225128, How sexual selection can drive the evolution of costly sperm ornamentation, Nature, 533, 7604, 535–8, 2016, Lüpold, Stefan, Manier, Mollie K, Puniamoorthy, Nalini, Schoff, Christopher, Starmer, William T, Luepold, Shannon H. Buckley, Belote, John M, Pitnick, Scott,weblink JOURNAL, 10.1038/533476a, 27225117, The bigger, the better, Nature, 533, 7604, 476, 2016, Gardiner, Jennifer R,

Market for human sperm

{{Further|Sperm donation}}Some sperm banks hold up to {{convert|170|l}} of sperm.NEWS, Sarfraz Manzoor, 2 November 2012,weblink Come inside: the world's biggest sperm bank, The Guardian, 4 August 2013, In addition to ejaculation, it is possible to extract sperm through TESE.On the global market, Denmark has a well-developed system of human 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.Assisted Reproduction in the Nordic Countries ncbio.org Furthermore, Nordic sperm donors tend to be tall and highly educatedFDA 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 transmission of Creutzfeldt–Jakob disease, although such a risk is insignificant, since artificial insemination is very different from the route of transmission of Creutzfeldt–Jakob disease.NEWS, Steven Kotler, 26 September 2007,weblink The God of Sperm, The prevalence of Creutzfeldt–Jakob disease for donors is at most one in a million, and if the donor was a carrier, the infectious proteins would still have to cross the blood-testis barrier to make transmission possible.

History

{{see also|Homunculus#Homunculus of spermists}}Sperm were first observed in 1677 by Antonie van LeeuwenhoekNEWS,weblink Timeline: Assisted reproduction and birth control, 2006-04-06, CBC News, using a microscope. He described them as being animalcules (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human.{{citation needed|date=January 2011}}

Forensic analysis

Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface.JOURNAL, 10.2174/1874402800801010012, Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source, The Open Forensic Science Journal, 1, 12–15, 2008, Fiedler, Anja, Rehdorf, Jessica, Hilbers, Florian, Johrdan, Lena, Stribl, Carola, Benecke, Mark, Sperm heads, e.g. from vaginal swabs, are still detected by microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining.JOURNAL, 11305439, 2001, Allery, J. P, Cytological detection of spermatozoa: Comparison of three staining methods, Journal of Forensic Sciences, 46, 2, 349–51, Telmon, N, Mieusset, R, Blanc, A, Rougé, D, 10.1520/JFS14970J, WEB,weblink The Presidents's DNA Initiative: Semen Stain Identification: Kernechtrot, Illinois State Police/President's DNA Initiative, 2009-12-10,

Sperm in plants

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.{{citation needed|date=January 2011}}

Motile sperm cells

(File:Plant sperm.png|thumb|Motile sperm cells of algae and seedless plants.BOOK, Raven, Peter H., Ray F. Evert, Susan E. Eichhorn, Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, 2005, New York, 0-7167-1007-2, )Motile sperm cells typically move via flagella and require a water medium in order to swim toward the egg for fertilization. In animals most of the energy for sperm motility is derived from the metabolism of fructose carried in the seminal fluid. This takes place in the mitochondria located in the sperm's midpiece (at the base of the sperm head). These cells cannot swim backwards due to the nature of their propulsion. The uniflagellated sperm cells (with one flagellum) of animals are referred to as spermatozoa, and are known to vary in size.{{citation needed|date=January 2011}}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).In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.JOURNAL, Bottino D, Alex Mogilner, Mogilner A, Roberts T, Stewart M, Oster G, How nematode sperm crawl, Journal of Cell Science, 115, Pt 2, 367–84, 2002, 11839788,

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 hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.BOOK, Sumbali, Geeta, The Fungi, Alpha Science Int'l Ltd., 2005, 1-84265-153-6, Fungal spermatia (also called pycniospores, especially in the Uredinales) 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 to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.JOURNAL, Maheshwari R, Microconidia of Neurospora crassa, Fungal Genetics and Biology, 26, 1, 1–18, 1999, 10072316, 10.1006/fgbi.1998.1103,

Sperm nuclei

In almost all embryophytes, 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 tube through 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 ovule for fertilization.In some 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 antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.

Sperm centrioles

Most sperm cells have centrioles in the sperm neck.JOURNAL, 4381714, 25883936, 10.3389/fcell.2015.00021, 3, Atypical centrioles during sexual reproduction, 2015, Front Cell Dev Biol, 21, Avidor-Reiss, T, Khire, A, Fishman, EL, Jo, KH, Sperm of many animals has 2 typical centrioles known as the proximal centriole and distal centriole. Some animals like human and bovine have a single typical centriole, known as the proximal centriole, and a second centriole with atypical structure. Mice and rats have no recognizable sperm centrioles. The fruit fly Drosophila melanogaster has a single centriole and an atypical centriole named the Proximal Centriole-Like (PCL).JOURNAL, May 2009, A Proximal Centriole-Like Structure Is Present in Drosophila Spermatids and Can Serve as a Model to Study Centriole Duplication, Genetics, 182, 1, 133–44, 10.1534/genetics.109.101709, 19293139, Blachon, S., Cai, X., Roberts, K. A., Yang, K., Polyanovsky, A., Church, A., Avidor-Reiss, T., 2674812,

Sperm tail formation

The sperm tail is a specialized type of cilium (aka flagella). In many animals the sperm tail is formed in a unique way, which is named Cytosolic ciliogenesis, since all or part of axoneme of the sperm tail is formed in the cytoplasm or get exposed to the cytoplasm.JOURNAL, 10.1016/j.cub.2015.11.001, 26654377, 5857621, Shared and Distinct Mechanisms of Compartmentalized and Cytosolic Ciliogenesis, Current Biology, 25, 23, R1143–50, 2015, Avidor-Reiss, Tomer, Leroux, Michel R,

See also

References

{{Reflist|2}}Fawcett, D. W. (1981) Sperm Flagellum. In: The Cell. D. W. Fawcett. Philadelphia, W. B. Saunders Company. 14: pp. 604-640.Lehti, M. S. and A. Sironen (2017). "Formation and function of sperm tail structures in association with sperm motility defects." Biol Reprod 97(4): 522-536.

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