Reproductive system

The reproductive system or genital system is a system of sex organs within an organism which work together for the purpose of sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system.[1] Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.[2]

Reproductive system
Details
Identifiers
Latinsystema reproductionis
TAA09.0.00.000
FMA7160 75572, 7160
Anatomical terminology

Animals

In mammals, the major organs of the reproductive system include the external genitalia (penis and vulva) as well as a number of internal organs, including the gamete-producing gonads (testicles and ovaries). Diseases of the human reproductive system are very common and widespread, particularly communicable sexually transmitted diseases.[3]

Most other vertebrate animals have generally similar reproductive systems consisting of gonads, ducts, and openings. However, there is a great diversity of physical adaptations as well as reproductive strategies in every group of vertebrates.

Vertebrates

Vertebrate animals all share key elements of their reproductive systems. They all have gamete-producing organs or gonads. In females, these gonads are then connected by oviducts to an opening to the outside of the body, typically the cloaca, but sometimes to a unique pore such as a vagina or intromittent organ.

Humans

The human reproductive system usually involves internal fertilization by sexual intercourse. During this process, the male inserts his erect penis into the female's vagina and ejaculates semen, which contains sperm. The sperm then travels through the vagina and cervix into the uterus or fallopian tubes for fertilization of the ovum. Upon successful fertilization and implantation, gestation of the fetus then occurs within the female's uterus for approximately nine months, this process is known as pregnancy in humans. Gestation ends with birth, the process of birth is known as labor. Labor consists of the muscles of the uterus contracting, the cervix dilating, and the baby passing out the vagina (the female genital organ). Human's babies and children are nearly helpless and require high levels of parental care for many years. One important type of parental care is the use of the mammary glands in the female breasts to nurse the baby.[4]

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 of sexual differentiation. In addition to differences in nearly every reproductive organ, numerous differences typically occur in secondary sexual characteristics.

The male reproductive system is a series of organs located outside of the body and around the pelvic region of a male 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 the testes which are housed in the temperature regulating scrotum, immature sperm then travel to the epididymis for development and storage. The second category are the ejaculatory fluid producing glands which include the seminal vesicles, prostate, and the vas deferens. The final category are those used for copulation, and deposition of the spermatozoa (sperm) within the male, these include the penis, urethra, vas deferens, and Cowper's gland.

Major secondary sexual characteristics includes: larger, more muscular stature, deepened voice, facial and body hair, broad shoulders, and development of an adam's apple. An important sexual hormone of males is androgen, and particularly testosterone.

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 the pelvic region of a female that contribute towards the reproductive process. The human female reproductive system contains three main parts: the vulva, which leads to the vagina, the vaginal opening, to the uterus; the uterus, which holds the developing fetus; and the ovaries, which produce the female's ova. The breasts 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 the vulva, which also includes the labia, clitoris and urethra; during intercourse this area is lubricated by mucus secreted by the Bartholin's glands. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the fallopian tubes. Each ovary contains hundreds of egg cells or ova (singular ovum).

Approximately every 28 days, the pituitary gland releases a hormone 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. It sita her 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 the endometrium, and unfertilized ova are shed each cycle through the process of menstruation. If the ovum is fertilized by sperm, it attaches to the endometrium and the fetus develops.

Other mammals

Joey in pouch
A newborn joey suckles from a teat found within its mother's pouch
Didactic model of a mammal urogenital system-FMVZ USP-17.jpeg
Didactic model of a mammal urogenital system.

Most mammal reproductive systems are similar, however, there are some notable differences between the non-human mammals and humans. For instance, most male mammals have a penis which is stored internally until erect, and most have a penis bone or baculum.[5] Additionally, males of most species do not remain continually sexually fertile as humans do. 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 their kidneys.[6]

The reproductive 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 a two-pronged penis, which corresponds to the females' two vaginae.[7][8] Marsupials typically develop their offspring in an external pouch containing teats to which their newborn young (joeys) attach themselves for post uterine development. Also, marsupials have a unique prepenial scrotum.[9] The 15mm (5/8 in) long newborn joey instinctively crawls and wriggles the several inches (15 cm), while clinging to fur, on the way to its mother's pouch.

The uterus and vagina are unique to mammals with no homologue in birds, reptiles, amphibians, or fish. In place of the uterus the other vertebrate groups have an unmodified oviduct leading directly to a cloaca, which is a shared exit-hole for gametes, urine, and feces. Monotremes (i.e. platypus and echidnas), a group of egg-laying mammals, also lack a uterus and vagina, 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 to 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).

Birds

Male and female birds have a cloaca, 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 intromittent organ which is known as a phallus that is analogous to the mammals' penis. The female lays amniotic 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 and oviduct.[10] As a group, birds, like mammals, are noted for their high level of parental care.

Reptiles

Reptiles are almost all sexually dimorphic, and exhibit internal fertilization through the cloaca. Some reptiles lay eggs 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 a pair of penis-like organs.

Frog in frogspawn
A male common frog in nuptial colors waiting for more females to come in a mass of spawn

Amphibians

Most amphibians exhibit external fertilization of eggs, typically within the water, though some amphibians such as caecilians have internal fertilization.[11] All have paired, internal gonads, connected by ducts to the cloaca.

Fish

Fish exhibit a wide range of different reproductive strategies. Most fish, however, are oviparous and exhibit external fertilization. In this process, females use their cloaca to release large quantities of their gametes, called spawn 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 anal fins that are modified into an intromittent organ analogous to the human penis.[12] A small portion of fish species are either viviparous or ovoviviparous, and are collectively known as livebearers.[13]

Fish gonads are typically pairs of either ovaries or testes. Most fish are sexually dimorphic but some species are hermaphroditic or unisexual.[14]

Invertebrates

Invertebrates have an extremely diverse array of reproductive systems, the only commonality may be that they all lay eggs. Also, aside from cephalopods and arthropods, nearly all other invertebrates are hermaphroditic and exhibit external fertilization.

Cephalopods

All cephalopods are sexually dimorphic and reproduce by laying eggs. Most cephalopods have semi-internal fertilization, in which the male places his gametes inside the female's mantle cavity or pallial cavity to fertilize the ova found in the female's single ovary.[15] Likewise, male cephalopods have only a single testicle. In the female of most cephalopods the nidamental 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 a hectocotylus. 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.

Insects

Most insects reproduce oviparously, i.e. by laying eggs. The eggs are produced by the female in a pair of ovaries. Sperm, produced by the male in one testis or more commonly two, is transmitted to the female during mating by means of external genitalia. The sperm is stored within the female in one or more spermathecae. At the time of fertilization, the eggs travel along oviducts to be fertilized by the sperm and are then expelled from the body ("laid"), in most cases via an ovipositor.

Arachnids

Arachnids may have one or two gonads, 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, or spermatophore. Complex courtship rituals have evolved in many arachnids to ensure the safe delivery of the sperm to the female.[16]

Arachnids usually lay yolky eggs, which hatch into immatures that resemble adults. Scorpions, however, are either ovoviviparous or viviparous, depending on species, and bear live young.

Plants

Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction.[17] Plants that are not flowering plants (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) 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 the pollination process involved both biotic and abiotic interactions.

Fungi

Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms.[18] 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 the life cycle of a species, the teleomorph and the anamorph.[19] 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-containing propagules.

See also

References

  1. ^ Introduction to the Reproductive System, Epidemiology and End Results (SEER) Program. Archived October 24, 2007, at the Wayback Machine.
  2. ^ Reproductive System 2001 Body Guide powered by Adam
  3. ^ STD's Today National Prevention Network, Center for Disease Control, United States Government, retrieving 2007
  4. ^ Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.
  5. ^ Schultz, Nicholas G., et al. "The baculum was gained and lost multiple times during mammalian evolution." Integrative and comparative biology 56.4 (2016): 644-656.
  6. ^ Werdelin L, Nilsonne A (January 1999). "The evolution of the scrotum and testicular descent in mammals: a phylogenetic view". J. Theor. Biol. 196 (1): 61–72. doi:10.1006/jtbi.1998.0821. PMID 9892556.
  7. ^ C. Hugh Tyndale-Biscoe (2005). Life of Marsupials. Csiro Publishing. ISBN 978-0-643-06257-3.
  8. ^ Don II Hunsaker (2 December 2012). The Biology of Marsupials. Elsevier Science. ISBN 978-0-323-14620-3.
  9. ^ Renfree, Marilyn; Tyndale-Biscoe, C. H. (1987). Reproductive physiology of marsupials. Cambridge, UK: Cambridge University Press. ISBN 0-521-33792-5.
  10. ^ Ritchison. BIO 554/754 Ornithology. Eastern Kentucky University.
  11. ^ Grzimek, B. (1974). Grzimek's Animal Life Encyclopedia: Volume 5 Fishes II & Amphibians. New York: Van Nostrand Reihnhold Co. pp. 301–302. ASIN B000HHFY52.
  12. ^ Fish Reproduction
  13. ^ Science, Biology, and Terminology of Fish reproduction: Reproductive modes and strategies-part 1. 2002. MARTIN MOE. THE BREEDER'S NET Online Magazine
  14. ^ Bony Fish Reproduction 2002. SeaWorld/Busch Gardens Animal Information Database.
  15. ^ Cephalopods. Archived 2007-10-20 at the Wayback Machine. The Living World of Molluscs. Robert Nordsieck.
  16. ^ Robert D. Barnes (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 596–604. ISBN 0-03-056747-5.
  17. ^ Barrett, S.C.H. (2002). "The evolution of plant sexual diversity" (PDF). Nature Reviews Genetics. 3 (4): 274–284. doi:10.1038/nrg776.
  18. ^ Alexopoulos et al., pp. 48–56.
  19. ^ Kirk et al., p. 633.

Cited literature

  • Alexopoulos CJ, Mims CW, Blackwell M (1996). Introductory Mycology. John Wiley and Sons. ISBN 0-471-52229-5.
  • Kirk PM, Cannon PF, Minter DW, Stalpers JA (2008). Dictionary of the Fungi (10th ed.). Wallingford, UK: CAB International. ISBN 0-85199-826-7.
Arachnid

Arachnids () are a class (Arachnida) of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Almost all adult arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ἀράχνη (aráchnē), from the myth of the hubristic human weaver Arachne who was turned into a spider. Spiders are the largest order in the class, which also includes scorpions, ticks, mites, harvestmen, and solifuges.Almost all extant arachnids are terrestrial, living mainly on land. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species.

Canine reproduction

Canine reproduction is the process of sexual reproduction in domestic dogs.

Egg cell

The egg cell, or ovum (plural ova), is the female reproductive cell (gamete) in oogamous organisms. The egg cell is typically not capable of active movement, and it is much larger (visible to the naked eye) than the motile sperm cells. When egg and sperm fuse, a diploid cell (the zygote) is formed, which rapidly grows into a new organism.

Equine anatomy

Equine anatomy refers to the gross and microscopic anatomy of horses and other equids, including donkeys, and zebras. While all anatomical features of equids are described in the same terms as for other animals by the International Committee on Veterinary Gross Anatomical Nomenclature in the book Nomina Anatomica Veterinaria, there are many horse-specific colloquial terms used by equestrians.

Female reproductive system

The female reproductive system is made up of the internal and external sex organs that function in reproduction of new offspring. In the human the female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a foetus to full term. The internal sex organs are the uterus, Fallopian tubes, and ovaries. The uterus or womb accommodates the embryo which develops into the foetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris, and vaginal opening. The vagina is connected to the uterus at the cervix.At certain intervals, the ovaries release an ovum, which passes through the Fallopian tube into the uterus. If, in this transit, it meets with sperm, a single sperm can enter and merge with the egg, fertilizing it.

Fertilization usually occurs in the Fallopian tubes and marks the beginning of embryogenesis. The zygote will then divide over enough generations of cells to form a blastocyst, which implants itself in the wall of the uterus. This begins the period of gestation and the embryo will continue to develop until full-term. When the foetus has developed enough to survive outside the uterus, the cervix dilates and contractions of the uterus propel the newborn through the birth canal (the vagina).

The corresponding equivalent among males is the male reproductive system.

Glans penis

The glans penis is a structure at the distal end of the penis in male mammals. It is the sensitive bulbous structure at the end of the human penis, and is anatomically homologous to the clitoral glans of the human female. The glans penis may be smooth, spiny, elongated, or divided in other mammals.

Typically, the glans is completely or partially covered by the foreskin in humans, except in men who have been circumcised. The foreskin can generally be retracted over and past the glans, and may automatically retract during an erection. The glans is more commonly known as the "head" or the "tip" of the penis. The medical name comes from the Latin words glans ('acorn') and penis ('of the penis') – the Latin genitive of this word has the same form as the nominative.

Gonad

A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes (sex cells) and sex hormones of an organism. In the female of the species the reproductive cells are the egg cells, and in the male the reproductive cells are the sperm. The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells. Both of these gametes, are haploid cells.

Male reproductive system

The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body and within the pelvis.

The main male sex organs are the penis and the testicles which produce semen and sperm, which, as part of sexual intercourse, fertilize an ovum in the female's body; the fertilized ovum (zygote) develops into a fetus, which is later born as an infant.

The corresponding system in females is the female reproductive system.

Marsupial

Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, possums, opossums, wombats, and Tasmanian devils. Some lesser-known marsupials are the potoroo and the quokka.

Marsupials represent the clade originating from the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they give birth to relatively undeveloped young that often reside in a pouch located on their mothers’ abdomen for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent (the mainland, Tasmania, New Guinea and nearby islands). The remaining 100 are found in the Americas — primarily in South America, but thirteen in Central America, and one in North America, north of Mexico.

The word marsupial comes from marsupium, the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and ultimately from the ancient Greek μάρσιππος mársippos, meaning "pouch".

Ovary

The ovary is an organ found in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilised by a sperm. There is an ovary (from Latin ovarium, meaning 'egg, nut') found on the left and right sides of the body. The ovaries also secrete hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause. It is also an endocrine gland because of the various hormones that it secretes.

Oviparity

Oviparous animals are animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, reptiles, all birds, and the monotremes.

In traditional usage, most insects, molluscs, and arachnids are also described as oviparous.

Reproductive system disease

A reproductive system disease is any disease of the reproductive system.

Scrotum

The scrotum is an anatomical male reproductive structure that consists of a suspended dual-chambered sack of skin and smooth muscle that is present in most terrestrial male mammals and located under the penis. One testis is typically lower than the other to avoid compression in the event of impact. The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which is found the scrotal septum. It appears as a thin longitudinal line that runs front to back over the entire scrotum. The scrotum contains the external spermatic fascia, testes, epididymis, and ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus. In humans and some other mammals, the scrotum becomes covered with pubic hair at puberty. The scrotum will usually tighten during penile erection and when exposed to cold temperature.

The scrotum is biologically homologous to the labia majora in females. Although present in most mammals, the external scrotum is absent in streamlined marine mammals, such as whales and seals, as well as in some lineages of land mammals, such as the afrotherians, xenarthrans, and numerous families of bats, rodents, and insectivores.

Seminal vesicle

The seminal vesicles (Latin: glandulae vesiculosae), vesicular glands, or seminal glands, are a pair of simple tubular glands posteroinferior to the urinary bladder of some male mammals. Seminal vesicles are located within the pelvis. They secrete fluid that partly composes the semen.

Smegma

Smegma (Greek smēgma) is a combination of shed skin cells, skin oils, and moisture. It occurs in both male and female mammalian genitalia. In female bodies, it collects around the clitoris and in the folds of the labia minora; in males, smegma collects under the foreskin.

Sperm

Sperm is the male reproductive cell and is derived from the Greek word (σπέρμα) sperma (meaning "seed"). In the types of sexual reproduction known as anisogamy and its subtype oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, whereas a non-motile sperm cell is referred to as a spermatium. Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell. In mammals, sperm develops in the testicles, is stored in the epididymis, and released from the penis.

Urethra

In anatomy, the urethra (from Greek οὐρήθρα – ourḗthrā) is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body. In males, the urethra travels through the penis and also carries semen. In human females (and in other primates), the urethra connects to the urinary meatus above the vagina, whereas in non-primates, the female's urethra empties into the urogenital sinus.Females use their urethra only for urinating, but males use their urethra for both urination and ejaculation. The external urethral sphincter is a striated muscle that allows voluntary control over urination. The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, is innervated by the sympathetic division of the autonomic nervous system. The internal sphincter is present both in males and females.

Uterus

The uterus (from Latin "uterus", plural uteri) or womb is a major female hormone-responsive secondary sex organ of the reproductive system in humans and most other mammals. In the human, the lower end of the uterus, the cervix, opens into the vagina, while the upper end, the fundus, is connected to the fallopian tubes. It is within the uterus that the fetus develops during gestation. In the human embryo, the uterus develops from the paramesonephric ducts which fuse into the single organ known as a simplex uterus. The uterus has different forms in many other animals and in some it exists as two separate uteri known as a duplex uterus.

In English, the term uterus is used consistently within the medical and related professions, while the Germanic-derived term womb is also commonly used in everyday contexts.

Zygote

A zygote (from Greek ζυγωτός zygōtos "joined" or "yoked", from ζυγοῦν zygoun "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information necessary to form a new individual. In multicellular organisms, the zygote is the earliest developmental stage. In single-celled organisms, the zygote can divide asexually by mitosis to produce identical offspring.

Oscar Hertwig and Richard Hertwig made some of the first discoveries on animal zygote formation.

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