This article is about the reproductive system of all types of organisms, including humans. For information specific to humans, seeHuman reproductive system.
Thereproductive system of an organism, also known as thegenital system, is the biological system made up of all the anatomicalorgans involved insexual reproduction. Many non-living substances such as fluids,hormones, andpheromones are also important accessories to the reproductive system.[1] Unlike mostorgan systems, thesexes ofdifferentiatedspecies often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greatergeneticfitness of theoffspring.[2]
In mammals, the major organs of the reproductive system include the externalgenitalia (penis andvulva) as well as a number of internal organs, including thegamete-producinggonads (testicles and ovaries). Diseases of the human reproductive system are very common and widespread, particularlycommunicablesexually transmitted infections.[3]
Most othervertebrates have similar reproductive systems consisting of gonads, ducts, and openings. However, there is a great diversity of physicaladaptations as well asreproductive strategies in every group of vertebrates.
Vertebrates share key elements of their reproductive systems. They all have gamete-producing organs known asgonads. In females, these gonads are then connected byoviducts to an opening to the outside of the body, typically the cloaca, but sometimes to a unique pore such as avagina.
The female reproductive system has two functions: The first is to produce egg cells, and the second is to protect and nourish the offspring until birth. The male reproductive system has one function, and it is to produce and deposit sperm. Humans have a high level ofsexual differentiation. In addition to differences in nearly every reproductive organ, numerous differences typically occur insecondary sexual characteristics.
The male reproductive system is a series of organs located outside of the body and around the pelvic region of amale that contribute towards the reproduction process. The primary direct function of the male reproductive system is to provide the male sperm for fertilization of the ovum.
The major reproductive organs of the male can be grouped into three categories. The first category is sperm production and storage. Production takes place in thetesticles, which are housed in the temperature regulatingscrotum, immature sperm then travel to theepididymides for development and storage. The second category is the ejaculatory fluid-producing glands which include theseminal vesicles,prostate, and thevasa deferentia. The final category are those used for copulation, and deposition of thespermatozoa (sperm) within the male, these include thepenis,urethra,vas deferens, andCowper's gland.
Major secondary sex characteristics include larger, more muscular stature, deepened voice,facial andbody hair, broad shoulders, and development of anAdam's apple. An important sexual hormone of males isandrogen, and particularlytestosterone.
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.
The human female reproductive system is a series of organs primarily located inside of the body and around thepelvic region of afemale that contribute towards thereproductive process. The human female reproductive system contains three main parts: thevulva, which leads to the vagina, 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.
The vagina meets the outside at thevulva, which also includes thelabia,clitoris andurethra; during intercourse, this area is lubricated by mucus secreted by theBartholin's glands. The vagina is attached to the uterus through thecervix, while the uterus is attached to the ovaries via thefallopian tubes. Each ovary contains hundreds of 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 ovum will move through herfallopian tubes and awaits the sperm for fertilization to occur. When this does not occur, i.e. no sperm for fertilization, the lining of the uterus, called theendometrium, and unfertilized ova are shed each cycle through the process ofmenstruation. If the ovum is fertilized by sperm, it will attach to the endometrium and embryonic development will begin.
Mostmammal reproductive systems are similar, however, there are some notable differences between the non-human mammals and humans. For instance, most male mammals havea penis which isstored internally until erect, and most have a penis bone orbaculum.[5] Additionally, both males and females of most species do not remain continuallysexually fertile as humans do and the females of most mammalian species don't grow permanentmammaries like human females do either. Like humans, most groups of mammals have descended testicles found within a scrotum, however, others have descended testicles that rest on the ventral body wall, and a few groups of mammals, such as elephants, have undescended testicles found deep within their body cavities near theirkidneys.[6]
Thereproductive system of marsupials is unique in that the female has two vaginae, both of which open externally through one orifice but lead to different compartments within the uterus; males usually have atwo-pronged penis, which corresponds to the females' two vaginae.[7][8] Marsupials typically develop their offspring in an externalpouch containingteats to which their newborn young (joeys) attach themselves for post uterine development. Also, marsupials have a unique prepenial scrotum.[9] The 15 mm (5⁄8 in) long newborn joey instinctively crawls and wriggles the 15 cm (6 in), while clinging to fur, on the way to its mother's pouch.
In regards to males, the mammalian penis has a similar structure in reptiles and a small percentage of birds while the scrotum is only present in mammals. Regarding females, the vulva is unique to mammals with no homologue in birds, reptiles, amphibians, or fish.[10][11][12] The clitoris, however, can be found in some reptiles and birds.[13] In place of the uterus and vagina, non-mammalvertebrate groups have an unmodified oviduct leading directly to acloaca, which is a shared exit-hole for gametes,urine, andfeces. Monotremes (i.e.platypus andechidnas), a group of egg-laying mammals, also lack a uterus, vagina, and vulva, and in that respect have a reproductive system resembling that of a reptile.
In domestic canines, sexual maturity (puberty) occurs between the ages of 6 and 12 months for both males and females, although this can be delayed until up to two years of age for some large breeds.
The mare's reproductive system is responsible for controlling gestation, birth, and lactation, as well as her estrous cycle and mating behavior. The stallion's reproductive system is responsible for his sexual behavior and secondary sex characteristics (such as a large crest).
The penises of even-toed ungulates have an S-shape at rest and lie in a pocket under the skin on the belly.[14] Thecorpora cavernosa are only slightly developed; and anerection mainly causes this curvature to extend, which leads to an extension, but not a thickening, of thepenis. Cetaceans have similar penises.[15] In some even-toed ungulates, the penis contains a structure called theurethral process[16][17][18] orpenile vermiform appendix.[19]
Male and female birds have acloaca, an opening through which eggs, sperm, and wastes pass. Intercourse is performed by pressing the lips of the cloacae together, which is sometimes known as anintromittent organ which is known as a phallus that isanalogous to themammals' penis. The female laysamniotic eggs in which the young fetus continues to develop after it leaves the female's body. Unlike most vertebrates, female birds typically have only one functional ovary andoviduct.[20] As a group, birds, like mammals, are noted for their high level of parental care.
Reptiles are almost allsexually dimorphic, and exhibit internal fertilization through the cloaca. Some reptiles layeggs while others are ovoviviparous (animals that deliver live young). Reproductive organs are found within the cloaca of reptiles. Most male reptiles have copulatory organs, which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median penis-like organ, while male snakes and lizards each possess apair of penis-like organs.
A malecommon frog in nuptial colors waiting for more females to come in a mass ofspawn
Mostamphibians exhibit external fertilization of eggs, typically within the water, though some amphibians such ascaecilians have internal fertilization.[21] All have paired, internal gonads, connected by ducts to the cloaca.
Fish exhibit a wide range of different reproductive strategies. Most fish, however, areoviparous and exhibit external fertilization. In this process, females use their cloaca to release large quantities of their gametes, calledspawn into the water and one or more males release "milt", a white fluid containing many sperm over the unfertilized eggs. Other species of fish are oviparous and have internal fertilization aided by pelvic or analfins that are modified into anintromittent organ analogous to the human penis.[22] A small portion of fish species are either viviparous orovoviviparous, and are collectively known aslivebearers.[23]
Fish gonads are typically pairs of either ovaries or testicles. Most fish are sexually dimorphic but some species arehermaphroditic orunisexual.[24]
Invertebrates have an extremely diverse array of reproductive systems, the only commonality may be that they all lay eggs. Also, aside fromcephalopods andarthropods, nearly all other invertebrates exhibitexternal fertilization.
Allcephalopods aresexually dimorphic and reproduce by layingeggs. Most cephalopods have semi-internal fertilization, in which the male places his gametes inside the female's mantle cavity orpallial cavity to fertilize theova found in the female's singleovary.[25] Likewise, male cephalopods have only a singletesticle. In the female of most cephalopods thenidamental glands aid in development of the egg.
The "penis" in most unshelled male cephalopods (Coleoidea) is a long and muscular end of the gonoduct used to transfer spermatophores to a modified arm called ahectocotylus. That in turn is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the "penis" is long and able to extend beyond the mantle cavity and transfer the spermatophores directly to the female.
Mostinsects reproduceoviparously, i.e. by layingeggs. The eggs are produced by the female in a pair ofovaries.Sperm, produced by the male in onetestis or more commonly two, is transmitted to the female duringmating by means of externalgenitalia. The sperm is stored within the female in one or morespermathecae. At the time offertilization, the eggs travel alongoviducts to be fertilized by the sperm and are then expelled from the body ("laid"), in most cases via anovipositor.
Arachnids may have one or twogonads, which are located in the abdomen. The genital opening is usually located on the underside of the second abdominal segment. In most species, the male transfers sperm to the female in a package, orspermatophore. Complex courtship rituals have evolved in many arachnids to ensure the safe delivery of the sperm to the female.[26]
Arachnids usually lay yolkyeggs, which hatch into immatures that resemble adults. Scorpions, however, are eitherovoviviparous orviviparous, depending on species, and bear live young.
Among all living organisms,flowers, which are the reproductive structures ofangiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction.[27] Plants that are not flowering plants (green algae,mosses,liverworts,hornworts,ferns andgymnosperms such asconifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations.Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time it was understood that thepollination process involved bothbiotic andabiotic interactions.
Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms.[28] It is estimated that a third of all fungi reproduce using more than one method of propagation; for example, reproduction may occur in two well-differentiated stages within thelife cycle of a species, theteleomorph and theanamorph.[29] Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containingpropagules.
^STD's TodayArchived 2014-10-25 at theWayback Machine National Prevention Network, Center for Disease Control, United States Government, retrieving 2007
^abUwe Gille (2008).urinary and sexual apparatus, urogenital Apparatus. In: F.-V. Salomon and others (eds.): Anatomy for veterinary medicine. pp. 368–403.ISBN978-3-8304-1075-1.
^Ritchison. BIO 554/754 Ornithology. Eastern Kentucky University.
^Grzimek, B. (1974).Grzimek's Animal Life Encyclopedia: Volume 5 Fishes II & Amphibians. New York: Van Nostrand Reihnhold Co. pp. 301–302.ASINB000HHFY52.
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