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| Human reproductive system | |
|---|---|
 Internalgenitalia of a human female (left) and male (right). | |
 External genitalia of an adult female (left) and male (right). | |
| Details | |
| Identifiers | |
| Latin | systemata genitalia |
| TA98 | A09.0.00.000 |
| TA2 | 3467 |
| FMA | 7160 75572, 7160 |
| Anatomical terminology | |
Thehuman reproductive system includes themale reproductive system, which functions to produce and depositsperm, and thefemale reproductive system, which functions to produceegg cells and to protect and nourish thefetus untilbirth. Humans have a high level ofsexual differentiation. In addition to differences in nearly every reproductive organ, there are numerous differences in typicalsecondary sex characteristics.
Human reproduction usually involvesinternal fertilization bysexual intercourse. In this process, themale inserts hiserectpenis into thefemale'svagina andejaculatessemen, which containssperm. A small proportion of the sperm pass through the cervix into the uterus and then into thefallopian tubes for fertilization of theovum. Only one sperm is required to fertilize the ovum. Upon successfulfertilization, the fertilized ovum, orzygote, travels out of the fallopian tube and into theuterus, where it implants in the uterine wall. This marks the beginning of gestation, better known aspregnancy, which continues for around nine months as the fetus develops. When the fetus has developed to a certain point, pregnancy is concluded withchildbirth, involving labor. During labor, the uterine muscles contract, and thecervix dilates typically over a period of hours, allowing the infant to pass from the uterus through the vagina.[1] Human infants are entirely dependent on their caregivers and requireparental care. Infants rely on their caregivers for comfort, cleanliness, and food. Food may be provided bybreastfeeding orformula feeding.[2]
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The human female reproductive system is a series of organs primarily located inside the body and around thepelvic region of afemale that contribute towards thereproductive process. The human female reproductive system contains three main parts: the vagina, which leads from thevulva, the vaginal opening, to the uterus; theuterus, which holds the developing fetus; and theovaries, which produce the female's ova. Thebreasts are involved during the parenting stage of reproduction, but in most classifications they are not considered to be part of the female reproductive system.[3]
The vagina meets the outside at thevulva, which is made up of thelabia,clitoris andvestibule;[4] during intercourse this area is lubricated by mucus secreted by theBartholin's glands. Thevagina is attached to the uterus through thecervix, while the uterus is attached to the ovaries via thefallopian tubes. Each ovary contains hundreds of egg cells or ova (singularovum).
Approximatelyevery 28 days, thepituitary gland releases ahormone that stimulates some of the ova to develop and grow. One ovum is released and it passes through the fallopian tube into the uterus. Hormones produced by the ovaries prepare the uterus to receive the ovum. The lining of the uterus, called theendometrium, and unfertilized ova are shed each cycle through the process ofmenstruation. If the ova is fertilized by sperm, it attaches to the endometrium and the fetus develops.[3]
The male reproductive system is a series of organs located outside the body and around thepelvis region of amale that contribute towards the reproduction process. The primary direct function of the male reproductive system is to provide the malesperm for fertilization of the ovum.[3]
The major reproductive organs of the male can be grouped into three categories. The first category produces and stores sperm (spermatozoa). These are produced in thetesticles, which are housed in the temperature-regulatingscrotum; immature sperm then travel to theepididymides for development and storage. The second category are the ejaculatory fluid producing glands which include theCowper's gland (also called bulbourethral gland),seminal vesicles,prostate, andvas deferens. The final category are those used forcopulation and deposition of the sperm within the female; these include thepenis,urethra, andvas deferens.[3]
Major secondary sexual characteristics include a larger, more muscular stature, deepened voice,facial andbody hair, broad shoulders, and the development of anAdam's apple.[5] An important sexual hormone of males isandrogen, particularlytestosterone.[6]
The testes release a hormone that controls the development of sperm. This hormone is also responsible for the development of physical characteristics in men, such as facial hair and a deep voice.
Thedevelopment of the reproductive system and thedevelopment of the urinary system are closely tied to thedevelopment of the human fetus. Despite the differences between them, theadultmale andfemale aredetermined in early development in the 6th week. The gonads and external genitals are derived from theintermediate mesoderm.[7] The three main fetal precursors of the reproductive organs are theWolffian duct, theMüllerian ducts, and thegonads.Endocrine hormones are a well-known and critical controlling factor in the normal differentiation of the reproductive system.[8]
The Wolffian duct forms theepididymis,vas deferens,ejaculatory duct, andseminal vesicle in the male reproductive system, but essentially disappears in the female reproductive system.[9] The reverse is true for the Müllerian duct, as it essentially disappears in the male reproductive system and forms the fallopian tubes, uterus, and vagina in the female system. In both sexes, the gonads go on to form the testes and ovaries; because they are derived from the same undeveloped structure, they are consideredhomologous organs. There are a number of other homologous structures shared between male and female reproductive systems. However, despite the similarity in function of the female fallopian tubes and the male epididymis and vas deferens, they are not homologous but ratheranalogous structures as they arise from different fetal structures.
Gametes are produced within the gonads through a process known asgametogenesis. This occurs when certain types ofgerm cells undergomeiosis to split the normaldiploid number ofchromosomes (n=46) intohaploid cells containing only 23 chromosomes.[10]
In males, this process is known asspermatogenesis and occurs only afterpuberty in theseminiferous tubules of the testes. The immaturespermatozoa or sperm are then sent to theepididymis, where they gain a tail, enablingmotility. Each of the original diploid germ cells or primaryspermatocytes forms four functional gametes, each forever young.[clarification needed] The production and survival of sperms require a temperature below the normal core body temperature. Since the scrotum, where the testes is present, is situated outside the body cavity, it provides a temperature about 3 °C below normal body temperature.
In females, gametogenesis is known asoogenesis; this occurs in theovarian follicles of the ovaries. This process does not produce mature ovum until puberty. In contrast with males, each of the original diploid germ cells or primaryoocytes will form only one mature ovum, and threepolar bodies which are not capable of fertilization. It has long been understood that in females, unlike males, all the primary oocytes ever found in a female will be created prior to birth, and that the final stages of ova production will then not resume until puberty.[10] However, recent scientific research has challenged that hypothesis.[11] This new research indicates that in at least some species of mammal, oocytes continue to be replenished in females well after birth.[12]
In malegerm cells andspermatozoa, and also in femaleoocytes, specialDNA repair mechanism are present that function to maintain the integrity of thegenomes that are to be passed on to progeny.[13] These DNA repair pathways includehomologous recombinational repair,non-homologous end joining,base excision repair andDNA mismatch repair.[13]
Like all complex organ systems, the human reproductive system is affected by many diseases. There are four main categories of reproductive diseases in humans. They are:
Specific reproductive diseases are oftensymptoms of other diseases anddisorders, or have multiple, or unknown causes making them difficult to classify. Examples of unclassifiable disorders arePeyronie's disease in males andendometriosis in females. Many congenital conditions cause reproductive abnormalities, but are better known for their other symptoms. These include:Turner syndrome,Klinefelter's syndrome,cystic fibrosis, andBloom syndrome.[15]
