mmpile/iStock/GettyImages
The process of reproduction in humans usually relies on sexual intercourse between a male and a female, although there are exceptions to this. Unlike many animals, humans mate throughout the year. Humans have sexual intercourse when sexual reproduction is not possible for reasons such as the use of birth control or female menopause. Practices and behaviors surrounding human reproduction vary widely across cultures, but in every case, it involves sperm, an ovum (egg), a uterus and a baby.
During meiosis, diploid cells divide into sperm in males and ova in females. During sexual intercourse, the male ejaculates semen, containing hundreds of millions of sperm into the vagina. If the female is ovulating, a sperm may encounter an ovum. When a sperm cell penetrates the ovum's barrier, its 23 chromosomes fuse with the ovum's 23, forming the zygote.
The zygote divides and multiplies many times. The growing embryo travels to the uterus, where it remains, and about 40 weeks after fertilization, a baby is born.
The process of reproduction in humans begins with meiosis. In human meiosis, diploid cells with the usual 46 chromosomes divide into four haploid daughter cells, each containing 23 chromosomes. Each of these daughter cells is called a gamete. In males, this meiotic process is called spermatogenesis, and the daughter cells are sperm. In females, the process is called oogenesis, and the daughter cells are called ova. Males begin spermatogenesis at puberty and continue throughout life. Healthy young adult males produce hundreds of millions of sperm each day. This number begins to decline by their mid-20s.
Unlike males, females begin to produce gametes before they even are even born. By the fifth month in the womb, female fetuses have begun oogenesis, but the process pauses after a phase called prophase I, suspending the ova in the primary oocyte stage until puberty. 99.9 percent of a females ova remain in the primary oocyte stage until they are eventually absorbed by the body. Millions are absorbed by the time a fetus is born, and by puberty, only 400,000 remain. For every ovulation, about 2,000 more ova are absorbed.
The four stages of the human sexual response cycle occur during partnered sex with people of any gender, as well as other sexual stimulation activities. The first stage is excitement, the beginning of arousal, in which blood flow increases and causes engorgement in the genitals and nipples, accompanied by an increase in heart rate, breathing rate, muscle tone and blood pressure. Next is the plateau stage, which is brief, and which involves an increase in arousal.
The third phase is orgasm, which involves waves of muscle spasms and pleasure that last several seconds. During this phase, the uterus has several contractions, and the penis has contractions at its base, causing semen, the fluid containing sperm, to ejaculate into the vagina. The last stage is resolution, during which the body relaxes to its original state.
The sperm take several minutes to travel through the vagina, cervix and uterus and reach the fallopian tubes. Out of hundreds of millions of sperm, one or two hundred make it that far. If the female is ovulating, the sperm can survive for up to 48 hours as the ovum travels down a fallopian tube from an ovary to meet the sperm. If the ovum is already in the fallopian tube, it can only survive 24 hours before the sperm reach it.
The ovum is encased in a protective coating called the zona pellucida. The sperm that reach the zona pellucida bind to it and then try to penetrate it. Eventually, one sperm succeeds, which causes chemical changes. This destroys the zona pellucidas sperm receptors so that no other sperm bind to it, and the zona pellucida hardens, blocking any remaining sperm attempting to cross the barrier. The sperm that made it through fuses with the ovum. The result is a zygote a one-celled diploid embryo.
The zygote undergoes a process called cleavage, in which it replicates itself by mitosis, and then continues to replicate, forming a multicelled blastocyst. The growing embryo travels from the fallopian tube to the uterus and attaches to the uterine lining, the endometrium, between days five and seven. Over the next few days, the embryo moves away from the endometrium and extends cells into it that become the umbilical cord and the placenta. The embryo receives nutrients and expels wastes via the umbilical cord.
By the eighth week, the embryo has become a fetus, with four limb buds and most of its major organ systems formed and external genitalia beginning to develop. During the second trimester, the fetus grows and develops its skeleton. Its movements become detectable by the parent. During the third trimester, the fetus continues to grow, and its respiratory and circulatory systems prepare for it to breathe air.
The process of birth typically happens after 40 weeks. It begins with the rupturing of the amniotic sac, which contained and protected the fetus, and the fluid inside spills out, which is known as water breaking. Hormones, especially oxytocin and prostaglandins, dilate the cervix and cause increasing uterine contractions to guide the fetus out through the birth canal. Over the course of minutes, hours or even days, the fetus is pushed out of the womb by uterine contractions followed by the placenta.
Some reproduction does not require intercourse but is the result of artificial insemination when a couple has fertility problems or a single prospective parent or a same-sex couple choose a sperm donor. Also, while male and female are simple terms for the biological processes of reproduction in humans, this language excludes the sexuality of transgender and intersex people. For example, a cisgender man (a man whose gender matches his birth sex) and a transgender man (a man who was assigned female at birth) who has not undergone sex reassignment surgery can have sexual intercourse with each other, and the transgender man can become pregnant.
The rest is here:
Process of Reproduction in Humans | Sciencing
- World Health Organization reference values for human semen characteristics [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- Economic consequences of overweight and obesity in infertility: a framework for evaluating the costs and outcomes of fertility care [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- Maternal metabolism and obesity: modifiable determinants of pregnancy outcome [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- Brain imaging studies of appetite in the context of obesity and the menstrual cycle [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- The impact of body mass index on semen parameters and reproductive hormones in human males: a systematic review with meta-analysis [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- Options for fertility preservation in prepubertal boys [Last Updated On: August 17th, 2024] [Originally Added On: April 6th, 2010]
- Xenografting of testicular tissue from an infant human donor results in accelerated testicular maturation [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Karyotype of miscarriages in relation to maternal weight [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Endoglandular trophoblast, an alternative route of trophoblast invasion? Analysis with novel confrontation co-culture models [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Regulation of extravillous trophoblast invasion by uterine natural killer cells is dependent on gestational age [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Functional regulation of thymic stromal lymphopoietin on proliferation and invasion of trophoblasts in human first-trimester pregnancy [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Home self-administration of vaginal misoprostol for medical abortion at 50-63 days compared with gestation of below 50 days [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Prospective study of the forearm bone mineral density of long-term users of the levonorgestrel-releasing intrauterine system [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Functional attenuation of human sperm by novel, non-surfactant spermicides: precise targeting of membrane physiology without affecting structure [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Characteristics indicating adenomyosis coexisting with leiomyomas: a case-control study [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- The risk of post-molar gestational trophoblastic neoplasia is higher in heterozygous than in homozygous complete hydatidiform moles [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Cumulative ongoing pregnancy rate achieved with oocyte vitrification and cleavage stage transfer without embryo selection in a standard infertility program [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Pregnancy outcome in female childhood cancer survivors [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Offering excess oocyte aspiration and vitrification to patients undergoing stimulated artificial insemination cycles can reduce the multiple pregnancy risk and accumulate oocytes for later use [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Avoidance of weekend oocyte retrievals during GnRH antagonist treatment by simple advancement or delay of hCG administration does not adversely affect IVF live birth outcomes [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Who should pay for assisted reproductive techniques? Answers from patients, professionals and the general public in Germany [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Sperm donor limits that control for the 'relative' risk associated with the use of open-identity donors [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Long-term cryostorage of sperm in a human sperm bank does not damage progressive motility concentration [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Screening for biomarkers of spermatogonia within the human testis: a whole genome approach [Last Updated On: August 17th, 2024] [Originally Added On: April 14th, 2010]
- Avoiding transgenerational risks of mitochondrial DNA disorders: a morally acceptable reason for sex selection? [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Cross border reproductive care in six European countries [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Morphometric dimensions of the human sperm head depend on the staining method used [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- ESX1 gene expression as a robust marker of residual spermatogenesis in azoospermic men [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Innovative virtual reality measurements for embryonic growth and development [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Consecutive or non-consecutive recurrent miscarriage: is there any difference in carrier status? [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- A longitudinal study of contraception and pregnancies in the same women followed for a quarter of a century [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Predictors of bleeding and user satisfaction during consecutive use of the levonorgestrel-releasing intrauterine system [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Direct proportional relationship between endometrioma size and ovarian parenchyma inadvertently removed during cystectomy, and its implication on the management of enlarged endometriomas [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Large prospective, pregnancy and infant follow-up trial assures the health of 1000 fetuses conceived after treatment with the GnRH antagonist ganirelix during controlled ovarian stimulation [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Altered aquaporin expression in women with polycystic ovary syndrome: hyperandrogenism in follicular fluid inhibits aquaporin-9 in granulosa cells through the phosphatidylinositol 3-kinase pathway [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Fast-release orodispersible tramadol as analgesia in hysterosalpingography with a metal cannula or a balloon catheter [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Xenotransplantation of cryopreserved human ovarian tissue into murine back muscle [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Predictors of psychological distress in patients starting IVF treatment: infertility-specific versus general psychological characteristics [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Psychological adjustment, knowledge and unmet information needs in women undergoing PGD [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Mothers of IVF and spontaneously conceived twins: a comparison of prenatal maternal expectations, coping resources and maternal stress [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Psychological well-being and sexarche in women with polycystic ovary syndrome [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Is human fecundity declining in Western countries? [Last Updated On: August 17th, 2024] [Originally Added On: May 20th, 2010]
- Impaired glucose tolerance, type 2 diabetes and metabolic syndrome in polycystic ovary syndrome: a systematic review and meta-analysis [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Current achievements and future research directions in ovarian tissue culture, in vitro follicle development and transplantation: implications for fertility preservation [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Human studies on genetics of the age at natural menopause: a systematic review [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Beyond oxygen: complex regulation and activity of hypoxia inducible factors in pregnancy [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Current knowledge of the aetiology of human tubal ectopic pregnancy [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Economic contraction and birth outcomes: an integrative review [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Teratogenic mechanisms of medical drugs [Last Updated On: August 17th, 2024] [Originally Added On: June 5th, 2010]
- Levels of semenogelin in human spermatozoa decrease during capacitation: involvement of reactive oxygen species and zinc [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Apoptosis and meiotic segregation in ejaculated sperm from Robertsonian translocation carrier patients [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- In humans, zona pellucida glycoprotein-1 binds to spermatozoa and induces acrosomal exocytosis [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Variants of the EPPIN gene affect the risk of idiopathic male infertility in the Han-Chinese population [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Epidermal clitoral inclusion cysts: not a rare complication of female genital mutilation [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- PCOSMIC: a multi-centre randomized trial in women with PolyCystic Ovary Syndrome evaluating Metformin for Infertility with Clomiphene [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Single versus double intrauterine insemination in multi-follicular ovarian hyperstimulation cycles: a randomized trial [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Soluble HLA-G is an independent factor for the prediction of pregnancy outcome after ART: a German multi-centre study [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Obstetric outcomes after transfer of vitrified blastocysts [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Occasional involvement of the ovary in Ewing sarcoma [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Y chromosome microdeletions, sperm DNA fragmentation and sperm oxidative stress as causes of recurrent spontaneous abortion of unknown etiology [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Development and preliminary validation of the fertility status awareness tool: FertiSTAT [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Xenotransplantation of human ovarian tissue to nude mice: comparison between four grafting sites [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Involvement of CFTR in oviductal HCO3- secretion and its effect on soluble adenylate cyclase-dependent early embryo development [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Effect of endometriosis on the protein expression pattern of follicular fluid from patients submitted to controlled ovarian hyperstimulation for in vitro fertilization [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Activin A regulates trophoblast cell adhesive properties: implications for implantation failure in women with endometriosis-associated infertility [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Clinical significance of sperm DNA damage in assisted reproduction outcome [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Fall in implantation rates following ICSI with sperm with high DNA fragmentation [Last Updated On: August 17th, 2024] [Originally Added On: June 17th, 2010]
- Prevalence of unsuspected uterine cavity abnormalities diagnosed by office hysteroscopy prior to in vitro fertilization [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Ultra-conservative fertility-sparing strategy for bilateral borderline ovarian tumours: an 11-year follow-up [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Fertility after autologous ovine uterine-tubal-ovarian transplantation by vascular anastomosis to the external iliac vessels [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Uterus transplantation in the baboon: methodology and long-term function after auto-transplantation [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Prestimulation parameters predicting live birth in anovulatory WHO Group II patients undergoing ovulation induction with gonadotrophins [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Transfer of a selected single blastocyst optimizes the chance of a healthy term baby: a retrospective population based study in Australia 2004-2007 [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Disclosure patterns of mode of conception among mothers and fathers-5-year follow-up of the Copenhagen Multi-centre Psychosocial Infertility (COMPI) cohort [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Assisted reproductive technology in Europe, 2006: results generated from European registers by ESHRE [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- A decade of sperm washing: clinical correlates of successful insemination outcome [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Sperm DNA integrity in cancer patients before and after cytotoxic treatment [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- Speriolin is a novel human and mouse sperm centrosome protein [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- No influence of body mass index on first trimester fetal growth [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]
- HLA sharing among couples appears unrelated to idiopathic recurrent fetal loss in Saudi Arabia [Last Updated On: August 17th, 2024] [Originally Added On: July 21st, 2010]