Human reproduction: Difference between revisions

'''Human reproduction''' is [[sexual reproduction]] that results in [[human fertilization]] to produce a human offspring. It typically<!-- NOTE: "Typically" is here because, as is clear from the rest of the lead and lower in the article, human reproduction can also be achieved via artificial insemination and assisted reproductive technology. Also, human cloning can theoretically be done, see [[animal cloning]].--> involves [[sexual intercourse]] between a [[sexual maturity|sexually mature]] human [[male]] and [[female]].<ref name=":1">{{Citation |last=Jones |first=Richard E. |title=The Male Reproductive System |date=1991 |work=Human Reproductive Biology |pages=72–93 |publisher=Elsevier |doi=10.1016/b978-0-12-389770-1.50008-1 |isbn=9780123897701 }}</ref> During sexual intercourse, the interaction between the [[male reproductive system|male]] and [[female reproductive system]]s results in [[fertilization]] of the [[ovum]] by the [[sperm]] to form a zygote.<ref name=":1" /> While normal cells contain 46 [[chromosome]]s (23 pairs), gamete cells only contain 23 single chromosomes, and it is when these two cells merge into one [[zygote]] cell that [[genetic recombination]] occurs and the new zygote contains 23 chromosomes from each parent, giving it 46 chromosomes (23 pairs).<ref name=":2">{{Cite web |title=Gametogenesis -– an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/medicine-and-dentistry/gametogenesis |access-date=2022-09-12 |website=www.sciencedirect.com}}</ref> The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 9-month [[gestation period]] that is followed by [[childbirth]]. The fertilization of the ovum may be achieved by [[artificial insemination]] methods, which do not involve sexual intercourse.<ref name=":3">{{Cite journal |last1=Ombelet |first1=W. |last2=Van Robays |first2=J. |date=2015 |title=Artificial insemination history: hurdles and milestones |journal=Facts, Views & Vision in ObGyn |volume=7 |issue=2 |pages=137–143 |issn=2032-0418 |pmc=4498171 |pmid=26175891 }}</ref> [[Assisted reproductive technology]] also exists.

Legal factors also play a vital role in the achievement of human reproduction: a [[Minor (law)|minor]] under the [[age of consent]] cannot give legal consent to sexual intercourse or artificial alternatives to reproduction, the former case of which is liable to have the older party charged with [[statutory rape]], depending on jurisdictions.<ref name="Cusack">{{cite book|author=Carmen M. Cusack|title=Laws Relating to Sex, Pregnancy, and Infancy: Issues in Criminal Justice|publisher=[[Springer Publishing|Springer]]|isbn=978-1137505194|year=2015|page=10|access-date=August 31, 2021|url=https://books.google.com/books?id=ZArACQAAQBAJ&pg=PT10|quote=Voluntary sexual intercourse with a post-pubescent minor who is younger than the legal age of consent is described as statutory rape. [...] In most states, age of consent is delimited between 16 years old and 18 years old. [...] In almost every jurisdiction, prepubescent children may not engage in any sexual contact. [...] Engaging in sexual contact with a prepubescent child is a serious criminal offense and a felony.|archive-date=May 9, 2021|archive-url=https://web.archive.org/web/20210509005922/https://books.google.com/books?id=ZArACQAAQBAJ&pg=PT10|url-status=live}}</ref><ref name=ojjdp>{{cite web |url=http://www.ncjrs.gov/pdffiles1/ojjdp/208803.pdf |title=Statutory Rape Known to Law Enforcement |access-date=2021-08-31 |publisher=U.S. Department of Justice - Office of Juvenile Justice and Delinquency Prevention |archive-date=2007-10-21 |archive-url=https://web.archive.org/web/20071021131957/http://www.ncjrs.gov/pdffiles1/ojjdp/208803.pdf |url-status=live }}</ref> Even for minors above the age of consent, [[comprehensive sex education]] advises both consenting parties to use [[contraception]] to avoid both [[sexually transmitted diseaseinfection]]s and [[Teenage pregnancy|early, unplanned/unwanted pregnancies]]. Pregnancy in girls under the age of 15 is especially discouraged due to their reproductive systems having yet to reach full maturity.<ref name=savethechildren>{{cite journal | author = Mayor S |title = Pregnancy and childbirth are leading causes of death in teenage girls in developing countries | journal = BMJ | volume = 328 | issue = 7449 | pages = 1152 | year = 2004 | pmid = 15142897 | pmc = 411126 | doi = 10.1136/bmj.328.7449.1152-a }}</ref>

The male reproductive system contains two main divisions: the [[testicle]]s where [[sperm]] are produced, and the [[human penis|penis]] which discharges the sperm aswhere [[semen]] (this is known[[ejaculated]] asthrough anthe [[ejaculationurethra]]). In humans, both of these organs are outside the [[abdominal cavity]]. Having the testicles outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3&nbsp;°C less than the normal body temperature i.e. 37&nbsp;°C. In particular, the extraperitoneal location of the testicles may result in a 2-fold reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissues compared to tissues at 37&nbsp;°C.<ref>{{cite journal | author = Baltz RH, Bingham PM, Drake JW | year = 1976 | title = Heat mutagenesis in bacteriophage T4: The transition pathway | journal = Proc. Natl. Acad. Sci. USA | volume = 73 | issue = 4| pages = 1269–1273 | pmid = 4797 | pmc = 430244 | doi = 10.1073/pnas.73.4.1269 | bibcode = 1976PNAS...73.1269B | doi-access = free }}</ref> If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external [[scrotum]] rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production.

The female reproductive system likewise contains two main divisions: the external genitalia (the [[Human vulva|vulva]]) and the internal genitalia.

[[File:Biological life cycle of humans 2.pngsvg|thumb|Basic processes involved: <br>1. [[sexual maturity|maturity]]; 2. [[spermatogenesis]] and [[oogenesis]]; 3. [[vaginal intercourse]] with [[internal fertilization]]; <br>4. [[zygote]]; 5. [[Human embryonic development|embryonic development]]; <br>6. [[childbirth]]; 7. [[adolescence]].]]

Human reproduction naturally takes place as [[internal fertilization]] by sexual intercourse. During this process, the man inserts his erect [[Human penis|penis]] into the woman's [[Human vagina|vagina]] and then either partner initiates rhythmic [[pelvic thrust]]s until the man achieves [[orgasm]], which leads to [[ejaculation]] of [[semen]] containing sperm into the vaginal canal. The sperm and the ovum are known as the [[gametes]] (each containing half the genetic information of the parent, created through [[meiosis]]).<ref name=":2" /> The sperm (being one of approximately 250 million sperm in a typical ejaculation) travels through the vagina and cervix into the uterus or fallopian tubes. Only 1 in 14 million of the ejaculated sperm will reach the fallopian tube. The egg simultaneously moves through the fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a [[zygote]]. Upon [[Human fertilization|fertilization]] and [[Implantation (human embryo)|implantation]], gestation of the fetus then occurs within the uterus.<ref>{{cite journal |author=Ghazal, S, Kulp Makarov, J |url=http://www.glowm.com/section_view/heading/Egg%20Transport%20and%20Fertilization/item/316 |title=Egg Transport and Fertilization |journal=The Global Library of Women's Medicine |year=2014 |issn=1756-2228 |doi=10.3843/GLOWM.10317 |access-date=May 8, 2016 |display-authors=etal |archive-date=May 13, 2016 |archive-url=https://web.archive.org/web/20160513065553/http://www.glowm.com/section_view/heading/Egg%20Transport%20and%20Fertilization/item/316 |url-status=live }}</ref><ref>{{cite web |url=https://www.ucsfhealth.org/education/conception_how_it_works/ |title=Conception: How It Works |publisher=The Regents of The University of California |year=2002 |access-date=May 8, 2016 |archive-date=March 15, 2016 |archive-url=https://web.archive.org/web/20160315083424/https://www.ucsfhealth.org/education/conception_how_it_works/ |url-status=live }}</ref><ref>{{cite web |url=http://www.completefertility.co.uk/fertility_basics.php |title=Fertility Basics |work=Complete Fertility Centre Southampton |publisher=Complete Fertility Ltd |year=2015 |access-date=May 8, 2016 |archive-date=May 8, 2016 |archive-url=https://web.archive.org/web/20160508060750/http://www.completefertility.co.uk/fertility_basics.php |url-status=live }}</ref><ref>{{cite web |url=http://www.webmd.com/baby/guide/understanding-conception |title=Conception & Pregnancy: Ovulation, Fertilization, and More |publisher=WebMD, LLC |year=2016 |access-date=May 8, 2016 |archive-date=May 8, 2016 |archive-url=https://web.archive.org/web/20160508202313/http://www.webmd.com/baby/guide/understanding-conception |url-status=live }}</ref>

[[Pregnancy rate#Pregnancy rate for sexual intercourse|Pregnancy rates for sexual intercourse]] are highest during the [[menstrual cycle]] time from some 5 days before until 1 to 2 days after ovulation.<ref>Pages.242,374 in: {{cite book|title=Taking Charge of Your Fertility|url=https://archive.org/details/takingchargeofyo00toni|url-access=registration|last=Weschler|first=Toni|publisher=HarperCollins|year=2002|isbn=0-06-093764-5|edition=Revised|location=New York|pages=[https://archive.org/details/takingchargeofyo00toni/page/359 359–361]}}</ref> For optimal pregnancy chance, there are recommendations of sexual intercourse every 1 or 2 days,<ref>{{cite web|url=https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/how-to-get-pregnant/art-20047611|title=How to get pregnant|website=[[Mayo Clinic]]|date=2016-11-02|access-date=2018-02-16|archive-date=2020-05-18|archive-url=https://web.archive.org/web/20200518223708/https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/how-to-get-pregnant/art-20047611|url-status=live}}</ref> or every 2 or 3 days.<ref>{{cite web|url=https://www.nice.org.uk/guidance/cg156/ifp/chapter/trying-for-a-baby|title=Fertility problems: assessment and treatment, Clinical guideline [CG156]|website=[[National Institute for Health and Care Excellence]]|access-date=2018-02-16|archive-date=2018-02-17|archive-url=https://web.archive.org/web/20180217082533/https://www.nice.org.uk/guidance/cg156/ifp/chapter/trying-for-a-baby|url-status=live}} Published date: February 2013. Last updated: September 2017</ref> Studies have shown no significant difference between different [[sex positions]] and pregnancy rate, as long as it results in [[ejaculation]] into the [[vagina]].<ref name=americanpregnancy>{{cite web|url=http://americanpregnancy.org/getting-pregnant-ebook/p7M7O0q1c71703C/gettingpregnant.pdf|title=The Essential Guide to Getting Pregnant|website=American Pregnancy Association|author=Dr. Philip B. Imler & David Wilbanks|access-date=2018-02-16|archive-url=https://web.archive.org/web/20180601033115/http://americanpregnancy.org/getting-pregnant-ebook/p7M7O0q1c71703C/gettingpregnant.pdf|archive-date=2018-06-01|url-status=dead}}</ref>

* Hopwood, Nick, [[Rebecca Flemming]], Lauren Kassell, eds. ''Reproduction: Antiquity to the Present Day'' (Cambridge UP, 2018). Illustrations. xxxv + 730 pp. {{ISBN|978-1-107-06802-5}} [https://www.amazon.com/Reproduction-Antiquity-Present-Nick-Hopwood/dp/1107068029/ excerpt] also [http://www.h-net.org/reviews/showpdf.php?id=53889 online review] 44 scholarly essays by historians.