Human fertilization - wikipedia Human fertilization Part of a series on Human growth and development Stages Human embryogenesis Fetus Infant Toddler Early childhood Child Preadolescence Adolescence Adult Middle age Old age Biological milestones Fertilization Childbirth Walking Language acquisition Puberty Menopause Ageing Death Development and psychology Pre - and perinatal Infant and child Adolescent Youth Young adult Adult Maturity Developmental stage theories Attachment Ecological Psychosocial Psychosexual development Moral Cognitive Cultural - historical Evolutionary Human body portal The acrosome reaction for a sea urchin, a similar process. Note that the picture shows several stages of one and the same spermatozoon - only one penetrates the ovum Illustration depicting ovulation and fertilization. The sperm entering the ovum using the acrosome head to break down the zona pellucida. Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. The result of this union is the production of a zygote cell, or fertilized egg, initiating prenatal development. Scientists discovered the dynamics of human fertilization in the nineteenth century. The process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization. Various exceptions to this sequence are possible, including artificial insemination, in vitro fertilization, external ejaculation without copulation, or copulation shortly after ovulation. Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg. The sperm plasma then fuses with the egg 's plasma membrane, the sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus. In vitro fertilization ( IVF ) is a process by which egg cells are fertilized by sperm outside the womb, in vitro. Contents 1 Anatomy 1.1 Corona radiata 1.2 Cone of attraction and perivitelline membrane 1.3 Sperm preparation 1.4 Zona pellucida 1.4. 1 Cortical reaction 2 Fusion 2.1 Cell membranes 2.2 Transformations 2.3 Replication 2.4 Mitosis 3 Fertilization age 4 Diseases 5 See also 6 References 7 External links Anatomy Corona radiata The sperm binds through the corona radiata, a layer of follicle cells on the outside of the secondary oocyte. Fertilization occurs when the nucleus of both a sperm and an egg fuse to form a diploid cell, known as zygote. The successful fusion of gametes forms a new organism. Cone of attraction and perivitelline membrane Where the spermatozoon is about to pierce, the yolk ( ooplasm ) is drawn out into a conical elevation, termed the cone of attraction or reception cone. Once the spermatozoon has entered, the peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa. Sperm preparation Further information : Acrosome reaction At the beginning of the process, the sperm undergoes a series of changes, as freshly ejaculated sperm is unable or poorly able to fertilize. The sperm must undergo capacitation in the female 's reproductive tract over several hours, which increases its motility and destabilizes its membrane, preparing it for the acrosome reaction, the enzymatic penetration of the egg 's tough membrane, the zona pellucida, which surrounds the oocyte. Zona pellucida After binding to the corona radiata the sperm reaches the zona pellucida, which is an extra-cellular matrix of glycoproteins. A special complementary molecule on the surface of the sperm head binds to a ZP3 glycoprotein in the zona pellucida. This binding triggers the acrosome to burst, releasing enzymes that help the sperm get through the zona pellucida. Some sperm cells consume their acrosome prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, sperm cells have on average 50 % genome similarity so the premature acrosomal reactions aid fertilization by a member of the same cohort. It may be regarded as a mechanism of kin selection. Recent studies have shown that the egg is not passive during this process. Cortical reaction Once the sperm cells find their way past the zona pellucida, the cortical reaction occurs. Cortical granules inside the secondary oocyte fuse with the plasma membrane of the cell, causing enzymes inside these granules to be expelled by exocytosis to the zona pellucida. This in turn causes the glyco - proteins in the zona pellucida to cross-link with each other -- i.e. the enzymes cause the ZP2 to hydrolyse into ZP2f -- making the whole matrix hard and impermeable to sperm. This prevents fertilization of an egg by more than one sperm. The cortical reaction and acrosome reaction are both essential to ensure that only one sperm will fertilize an egg. Fusion Fertilization and implantation in humans. After the sperm enters the cytoplasm of the oocyte ( also called ovocyte ), the tail and the outer coating of the sperm disintegrate and the cortical reaction takes place, preventing other sperm from fertilizing the same egg. The oocyte now undergoes its second meiotic division producing the haploid ovum and releasing a polar body. The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material. Cell membranes The fusion of cell membranes of the secondary oocyte and sperm takes place. Transformations In preparation for the fusion of their genetic material both the oocyte and the sperm undergo transformations as a reaction to the fusion of cell membranes. The oocyte completes its second meiotic division. This results in a mature ovum. The nucleus of the oocyte is called a pronucleus in this process, to distinguish it from the nuclei that are the result of fertilization. The sperm 's tail and mitochondria degenerate with the formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin. Still, a considerable amount of RNA from the sperm is delivered to the resulting embryo and likely influences embryo development and the phenotype of the offspring. Replication The pronuclei migrate toward the center of the oocyte, rapidly replicating their DNA as they do so to prepare the zygote for its first mitotic division. Mitosis Usually 23 chromosomes from spermatozoon and 23 chromosomes from egg cell fuse ( half of spermatozoons carry X chromosome and the other half Y chromosome ). Their membranes dissolve, leaving no barriers between the male and female chromosomes. During this dissolution, a mitotic spindle forms between them. The spindle captures the chromosomes before they disperse in the egg cytoplasm. Upon subsequently undergoing mitosis ( which includes pulling of chromatids towards centrioles in anaphase ) the cell gathers genetic material from the male and female together. Thus, the first mitosis of the union of sperm and oocyte is the actual fusion of their chromosomes. Each of the two daughter cells resulting from that mitosis has one replica of each chromatid that was replicated in the previous stage. Thus, they are genetically identical. Fertilization age Fertilization is the event most commonly used to mark the zero point in descriptions of prenatal development of the embryo or fetus. The resultant age is known as fertilization age, fertilizational age, embryonic age, fetal age or ( intrauterine ) developmental ( IUD ) age. Gestational age, in contrast, takes the beginning of the last menstrual period ( LMP ) as the zero point. By convention, gestational age is calculated by adding 14 days to fertilization age and vice versa. In fact, however, fertilization usually occurs within a day of ovulation, which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation ( LMP ). There is also considerable variability in this interval, with a 95 % prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP - to - ovulation time of 14.6. In a reference group representing all women, the 95 % prediction interval of the LMP - to - ovulation is 8.2 to 20.5 days. The average time to birth has been estimated to be 268 days ( 38 weeks and two days ) from ovulation, with a standard deviation of 10 days or coefficient of variation of 3.7 %. Fertilization age is sometimes used postnatally ( after birth ) as well to estimate various risk factors. For example, it is a better predictor than postnatal age for risk of intraventricular hemorrhage in premature babies treated with extracorporeal membrane oxygenation. Diseases Various disorders can arise from defects in the fertilization process. Polyspermy results from multiple sperm fertilizing an egg. However, some researchers have found that in rare pairs of fraternal twins, their origin might have been from the fertilization of one egg cell from the mother and eight sperm cells from the father. This possibility has been investigated by computer simulations of the fertilization process. See also Spontaneous conception, the unassisted conception of a subsequent child after prior use of assisted reproductive technology References Jump up ^ Garrison, Fielding. An Introduction to the History of Medicine, pages 566 - 567 ( Saunders 1921 ). Jump up ^ `` Archived copy ''. Archived from the original on 2011 - 12 - 22. Retrieved 2016 - 01 - 24. Jump up ^ `` Can Pregnancy Occur - Pregnancy Myths on How Pregnancy Occurs ''. americanpregnancy.org. 23 April 2012. Archived from the original on 6 July 2014. Retrieved 30 April 2018. Jump up ^ Lawyers Guide to Forensic Medicine SBN 978 - 1 - 85941 - 159 - 9 By Bernard Knight - Page 188 `` Pregnancy is well known to occur from such external ejaculation... '' Jump up ^ `` Fertilization of the Ovum ''. Gray 's Anatomy. Archived from the original on 2010 - 12 - 02. Retrieved 2010 - 10 - 16. Jump up ^ `` Fertilization ''. Archived from the original on 24 June 2010. Retrieved 28 July 2010. Jump up ^ Angier, Natalie ( 2007 - 06 - 12 ). `` Sleek, Fast and Focused : The Cells That Make Dad Dad ''. The New York Times. Archived from the original on 2017 - 04 - 29. Jump up ^ Suzanne Wymelenberg, Science and Babies, National Academy Press, page 17 Jump up ^ Richard E. Jones and Kristin H. Lopez, Human Reproductive Biology, Third Edition, Elsevier, 2006, page 238 Jump up ^ `` Fertilization : The Cortical Reaction ''. Boundless. Boundless. Retrieved 14 March 2013. Jump up ^ Jodar, M. ; Selvaraju, S. ; Sendler, E. ; Diamond, M.P. ; Krawetz, S.A. ; for the Reproductive Medicine Networks ( 2013 ). `` The presence, role and clinical use of spermatozoal RNAs ''. Human Reproduction Update. 19 ( 6 ) : 604 -- 624. doi : 10.1093 / humupd / dmt031. PMC 3796946. PMID 23856356. ^ Jump up to : Marieb, Elaine M. Human Anatomy and Physiology, 5th ed. pp. 1119 - 1122 ( 2001 ). ISBN 0 - 8053 - 4989 - 8 Jump up ^ `` Archived copy ''. Archived from the original on 2016 - 10 - 06. Retrieved 2016 - 07 - 31. Jump up ^ Wagner F, Erdösová B, Kylarová D ( December 2004 ). `` Degradation phase of apoptosis during the early stages of human metanephros development ''. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 148 ( 2 ) : 255 -- 6. doi : 10.5507 / bp. 2004.054. PMID 15744391. Jump up ^ Robinson, H.P. ; Fleming, J.E.E. ( 1975 ). `` A Critical Evaluation of Sonar `` crown - Rump Length '' Measurements ``. BJOG : an International Journal of Obstetrics and Gynaecology. 82 ( 9 ) : 702 -- 710. doi : 10.1111 / j. 1471 - 0528.1975. tb00710. x. ^ Jump up to : Geirsson RT ( May 1991 ). `` Ultrasound instead of last menstrual period as the basis of gestational age assignment ''. Ultrasound Obstet Gynecol. 1 ( 3 ) : 212 -- 9. doi : 10.1046 / j. 1469 - 0705.1991. 01030212. x. PMID 12797075. Jump up ^ Derived from a standard deviation in this interval of 2.6, as given in : Fehring RJ, Schneider M, Raviele K ( 2006 ). `` Variability in the phases of the menstrual cycle ''. J Obstet Gynecol Neonatal Nurs. 35 ( 3 ) : 376 -- 84. doi : 10.1111 / j. 1552 - 6909.2006. 00051. x. PMID 16700687. Jump up ^ Jukic AM, Baird DD, Weinberg CR, McConnaughey DR, Wilcox AJ ( 2013 ). `` Length of human pregnancy and contributors to its natural variation ''. Hum. Reprod. 28 ( 10 ) : 2848 -- 55. doi : 10.1093 / humrep / det297. PMC 3777570. PMID 23922246. Jump up ^ Jobe, Alan H ( 2004 ). `` Post-conceptional age and IVH in ECMO patients ''. The Journal of Pediatrics. 145 ( 2 ) : A2. doi : 10.1016 / j. jpeds. 2004.07. 010. External links Fertilization ( Conception ) Human physiology of sexual reproduction Menstrual cycle Menarche Menstruation Follicular phase Ovulation Luteal phase Gametogenesis Spermatogenesis spermatogonium spermatocyte spermatid sperm ) Oogenesis ( oogonium oocyte ootid ovum ) Germ cell gonocyte gamete ) Human sexual activity Sexual arousal Sexual intercourse Masturbation Erection Orgasm Ejaculation Insemination Fertilization / Fertility Implantation Pregnancy Postpartum period Mechanics of sex Development of the reproductive system Sexual differentiation Sexual dimorphism Feminization Virilization ) Puberty Gonadarche Tanner scale Pubarche Menarche Spermarche Adrenarche ) Maternal age / Paternal age Menopause Egg Ovum Oviposition Oviparity Ovoviviparity Vivipary Reproductive endocrinology and infertility Hypothalamic -- pituitary -- gonadal axis Hypothalamic -- pituitary -- prolactin axis Andrology Hormone Breast Thelarche Development Lactation Breastfeeding Retrieved from `` https://en.wikipedia.org/w/index.php?title=Human_fertilization&oldid=848347329 '' Categories : Fertility Hidden categories : All articles with unsourced statements Articles with unsourced statements from June 2014 Talk Contents About Wikipedia Bosanski Čeština Deutsch فارسی Français Hrvatski Italiano Latviešu नेपाली Polski Português Русский Slovenčina Slovenščina 6 more Edit links This page was last edited on 1 July 2018, at 10 : 52 ( UTC ). 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Question: what do we call the moment when the sperm and ovum join
Answer: Human fertilization