اسپرم

از ویکی‌پدیا، دانشنامهٔ آزاد
پرش به ناوبری پرش به جستجو
فارسیEnglish
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اسپرم
Sperm-egg.jpg
Complete diagram of a human spermatozoa en.svg
بخش‌های اسپرم
جزئیات
لاتین spermatozoon
شناسه‌ها
فهرست گری p.۱۲۴۳
سرعنوان پزشکی A05.360.490.890
دورلندز
/السویر		 Spermatozoa
واژگان کالبدشناسی
بخش‌های اسپرم
فیلم حرکت سلول‌های اسپرم زیر میکروسکوپ

اِسپِرم یا نر یاخته یا زامه به یاخته‌های جنسی جانور نر می‌گویند که در غده‌های جنسی تولید می‌شود. اسپرم یا اسپرماتوزوآی بالغ یاختهٔ جنسی (گامت) جنس نر در بیشتر جاندارانی است که به روش جنسی بارور می‌شوند. اسپرم تک‌دسته است. اسپرم برای تحرک خود فروکتوز (نوعی قند) را که در منی وجود دارد در میتوکندری‌های خود می‌سوزاند و به انرژی تبدیل می‌کند.[۱]

در انسان اسپرم در بیضه آغاز به ساخته شدن می‌کند و پس از تکامل در برخایه، با منی از بدن خارج می‌شود. اشکال در ساخت یا آزادسازی اسپرم می‌تواند موجب ناباروری مردان شود. در واقع تولید اسپرم یکی از پیچیده‌ترین و طولانی‌ترین فرایندها در بدن است که با تخصصی شدن سلول‌های جنسی اولیه در دوران جنینی آغاز می‌شود و بعد با اسپرم‌سازی و تمایز اسپرم در بیضه‌ها در دوران بلوغ ادامه پیدا می‌کند.

بر پایهٔ برخی پژوهش‌ها تولید اسپرم در همهٔ جانداران به ۶۰۰ میلیون سال پیش برمی‌گردد. تولید اسپرم در همهٔ جانداران تحت تأثیر ژنی به نام بول (به انگلیسی:Boule) است. این ژن در طی تکامل انسان از آغاز تاکنون بی‌تغییر باقی مانده‌است و در همهٔ جانداران وجود دارد.[۲]

تولید اسپرم[ویرایش]

در انسان با فرا رسیدن زمان بلوغ، ساخت همیشگی اسپرم در بیضه‌ها با سرعت حدود ۱۲۵ میلیون اسپرم در روز آغاز می‌شود (در هر ثانیه حدود ۱۵۰۰ اسپرم). اسپرم‌ها در اطراف دیواره‌های لوله‌های سمینیفر تکامـل پیدا می‌کنند و دم‌های آن‌ها که آن‌ها را قادر به شنا کردن می‌کنند، به سمت مرکز لوله‌ها قرار می‌گیرند. اسپرم بالغ در یک لولهٔ پیچ در پیچ به نام اپیدیدیم که پشت هر بیضه جای دارد، نگهداری می‌شود. سرانجام اسپرم‌ها یا در طی فعالیت جنسی با انزال بیرون می‌روند یا به داخل بدن بازجذب می‌شوند.[۳]

کاهش تولید[ویرایش]

از دلایل کاهش تولید اسپرم در مردان می‌توان به کشیدن سیگار، اضافه وزن، تغذیه و هر چه باعث گرم شدن بیضه‌ها شود که می‌توان به نشستن طولانی مدت اشاره کرد. همچنین ورزش تأثیر بسیاری بر تولید اسپرم دارد به نحوی که مردانی که در طول روز بیش از ۱۵ ساعت تحرک دارند حدود ۷۳ درصد نسبت به مردان کم‌تحرک اسپرم تولید می‌کنند. کاهش تولید اسپرم در مردان لزوماً به ضعف قدرت باروری منجر نمی‌شود.[۴] اسپرم انسان در بدن زن چهار تا پنج روز زنده می‌ماند اما بیرون بدن مدت بسیار کوتاهی زنده می‌ماند.

کیفیت اسپرم[ویرایش]

سال‌هاست که پژوهش‌گران در تلاش‌اند ارتباط میان جذابیت ظاهری و قدرت باروری مردان را مشخص کنند. اما همواره نتایج درهم و متغیر بوده‌است. اخیراً پژوهشی از ژورنال زیست‌شناسی تکاملی گام مهمی در این زمینه برداشته و به دو یافتهٔ مهم دست‌یافته‌است: ۱- بله، به‌طورکلی مردانِ جذاب‌تر و ظریفتر اسپرم سالم‌تری دارند، ۲- هرچه فرد چهرهٔ مردانه‌تر داشته باشد اسپرم جنب و جوش کمتری دارد. دستاورد اصلی بررسی فوق در این نهفته بود که توانستند به مقایسه ایی بین توانایی اسپرم و مردانه بودن چهره‌ها دست یابند. به عبارت دقیقتر هر چه قدر صورت و گونه مردان برجسته تر و پهن‌تر باشد اسپرم‌های تنبل و بی رمق تری دارند.

پژوهش هیچ دلیل روشن و دقیقی برای این ارتباط ذکر نکرده است ولی اشاره به این فرضیه شد که افراد دارای چهره‌های مردانه سکس بیشتری داشته‌اند و به همین دلیل نیازی به اسپرم‌های سریع و پر انرژی برای حامله‌کردن شریک جنسی‌شان نبود. درحالی‌که افراد فاقد چهره و هیبت مردانه (و بدن غیرعضلانی تر) شانس کمتری برای رابطهٔ جنسی داشتند و نیاز تطبیقی شان طوری تنظیم شده‌است که بیشترین بهره را از این شانس کم ببرند. بنابر این شرط بقا، امکان برای شان فراهم شده‌است که اسپرمی با شانس باروری زیاد (حجم، تعداد و سرعت) تولید کنند.[۵]

اسپرم آزمایشگاهی[ویرایش]

در فوریه ۲۰۱۶ پژوهشگران چینی موفق شدند با تولید اسپرم در آزمایشگاه، بچه موش‌های سالم تولید کنند. بچه موش‌هایی که از این اسپرم‌های آزمایشگاهی به دنیا آمدند نه فقط سالم بودند بلکه خود نیز صاحب بچه‌هایی سالم شدند. در واقع آن‌ها فرایند میوز آزمایشگاهی را تکمیل کردند و برای تولید اسپرم در آزمایشگاه از سلول‌های بنیادی جنینی استفاده کردند. پژوهشگران چینی با استفاده از محیط کشت سه بعدی، هورمون‌ها، مواد شیمیایی و بافت بیضه این سلول‌های چند قابلیتی (multipotent) را به سوی اسپرم شدن سوق دادند. البته آنچه پژوهشگران تولید کردند یک مرحله پیش از تکامل نهایی اسپرم است، مرحله‌ای که به آن اسپرماتید می‌گویند.[۶]

جستارهای وابسته[ویرایش]

منابع[ویرایش]

  • ویکی‌پدیای انگلیسی
  1. ↑ از اسپرم آزمایشگاهی بچه‌موش‌های 'سالم و بارور به دنیا آمدند' بی‌بی‌سی فارسی
  2. ↑ Sperm in All Animals Originated 600 Million Years Ago «ancient-sperm-gene». بازبینی‌شده در ۰۹/۱۰/۲۰۱۱. 
  3. ↑ «آلت تناسلی مرد وزن». www.pezeshkan.org. بازبینی‌شده در ۰۹/۱۰/۲۰۱۱. 
  4. ↑ «تماشای بیش از حد تلویزیون و کاهش اسپرم‌های مردان». دویچه وله فارسی، ۲۴ فوریه ۲۰۱۳. بازبینی‌شده در ۲۴ فوریه ۲۰۱۳. 
  5. ↑ «یال و کوپال مردانه بیشتر، اسپرم ضعیفتر». مرد روز، ۱۰ سپتامبر ۲۰۱۴. 
  6. ↑ http://www.cell.com/cell-stem-cell/fulltext/S1934-5909(16)00018-7
در ویکی‌انبار پرونده‌هایی دربارهٔ اسپرم موجود است.
For other uses, see Sperm (disambiguation).
Diagram of a human sperm cell

Sperm is the male reproductive cell and is derived from the Greek word (σπέρμα) sperma (meaning "seed"). 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, stored in the epididymis, and is released from the penis.

Video of human sperm cells recorded by an affordable home microscope.

Sperm in animals

Further information: 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

Sperm and egg fusing

The mammalian sperm cell can be divided in 4 parts:

  • head: it contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. It also contains vacuoles.[1]
  • midpiece: it 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.
  • tail or "flagellum": it executes the lashing movements that propel the spermatocyte.[4]

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.[5]

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. The spermatid stage is where the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan.[6] Sperm 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.[7] 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.[8]

Sperm quality

Human sperm stained for semen quality testing.
Main article: Semen quality

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.[9] (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.[10] (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.[11] 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.[12] 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.[13] 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.[14][15]

Market for human sperm

Further information: Sperm donation

Some sperm banks hold up to 170 litres (37 imp gal; 45 US gal) of sperm.[16]

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[17] 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.[17] Furthermore, Nordic sperm donors tend to be tall and highly educated[18] and have altruistic motives for their donations,[18] 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.[17] 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.[19] 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.[19]

History

See also: Homunculus § Homunculus of spermists

Sperm were first observed in 1677 by Antonie van Leeuwenhoek[20] 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]

Forensic analysis

Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface.[21] Sperm heads, e.g. from vaginal swabs, are still detected by microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining.[22][23]

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]

Motile sperm cells

Motile sperm cells of algae and seedless plants.[24]

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]

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).[24]

In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.[25]

Non-motile sperm cells

Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in a spermatangium.[24]

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.[24] 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.[26]

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.[27]

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.[24]

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.[24]

Sperm centrioles

Most sperm cells have centrioles in the sperm neck [28]. 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.[2] Mice and rat have no recognizable sperm centrioles. The fruit fly Drosophila melanogaster has a single centriole and an atypical centriole named the Proximal Centriole-Like (PCL) [29].

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.[30]

See also

References

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  2. ^ a b 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 (2018). "A novel atypical sperm centriole is functional during human fertilization". Nature Communications. 9 (1): 2210. doi:10.1038/s41467-018-04678-8. PMID 29880810. 
  3. ^ Blachon, S; Cai, X; Roberts, K. A; Yang, K; Polyanovsky, A; Church, A; Avidor-Reiss, T (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. doi:10.1534/genetics.109.101709. PMC 2674812 Freely accessible. PMID 19293139. 
  4. ^ Ishijima, Sumio; Oshio, Shigeru; Mohri, Hideo (1986). "Flagellar movement of human spermatozoa". Gamete Research. 13 (3): 185–197. doi:10.1002/mrd.1120130302. 
  5. ^ Hewitson, Laura & Schatten, Gerald P. (2003). "The biology of fertilization in humans". In Patrizio, Pasquale et al. A color atlas for human assisted reproduction: laboratory and clinical insights. Lippincott Williams & Wilkins. p. 3. ISBN 978-0-7817-3769-2. Retrieved 2013-11-09. 
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  7. ^ 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. doi:10.1095/biolreprod31.5.888. 
  8. ^ Cyranoski, David (2016). "Researchers claim to have made artificial mouse sperm in a dish". Nature. doi:10.1038/nature.2016.19453. 
  9. ^ Gurevich, Rachel (2008-06-10). "Does Age Affect Male Fertility?". About.com. Retrieved 14 February 2010. 
  10. ^ Gavriliouk D, Aitken RJ (2015). "Damage to Sperm DNA Mediated by Reactive Oxygen Species: Its Impact on Human Reproduction and the Health Trajectory of Offspring". Advances in Experimental Medicine and Biology. Advances in Experimental Medicine and Biology. 868: 23–47. doi:10.1007/978-3-319-18881-2_2. ISBN 978-3-319-18880-5. PMID 26178844. 
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  13. ^ Marchetti F, Bishop J, Gingerich J, Wyrobek AJ (2015). "Meiotic interstrand DNA damage escapes paternal repair and causes chromosomal aberrations in the zygote by maternal misrepair". Scientific Reports. 5: 7689. doi:10.1038/srep07689. PMC 4286742 Freely accessible. PMID 25567288. 
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  15. ^ Gardiner, Jennifer R (2016). "The bigger, the better". Nature. 533 (7604): 476. doi:10.1038/533476a. PMID 27225117. 
  16. ^ Sarfraz Manzoor (2 November 2012). "Come inside: the world's biggest sperm bank". The Guardian. Retrieved 4 August 2013. 
  17. ^ a b c Assisted Reproduction in the Nordic Countries ncbio.org
  18. ^ a b FDA Rules Block Import of Prized Danish Sperm Posted Aug 13, 08 7:37 AM CDT in World, Science & Health
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External links

Preceded by
None		 Stages of human development
Sperm + Oocyte		 Succeeded by
Zygote
برگرفته از «https://fa.wikipedia.org/w/index.php?title=اسپرم&oldid=22180133»