n.
The bodily system of gonads, associated ducts, and external genitals concerned with sexual reproduction.
reproductive system
| Dictionary: reproductive system |
n.
| Sci-Tech Encyclopedia: Reproductive system |
The structures concerned with the production of sex cells (gametes) and perpetuation of the species. The reproductive function constitutes the only vertebrate physiological function that necessitates the existence of two morphologically different kinds of individuals in eac animal species, the males and the females (sexual dimorphism). The purpose of the reproductive function is fertilization, that is, the fusion of a male and a female sex cell produced by twodistinct individuals.
Anatomy
Egg cells, or ova, and sperm cells, or spermatozoa, are formed in the primary reproductive organs, which are collectively known as gonads. Those of the male are called testes; those of the female are ovaries. The gonads are paired structures, although in some forms what appears to be an unpaired gonad is the result either of fusion of paired structures or of unilateral degeneration.
The reproductive elements formed in the gonads must be transported to the outside of the body. In most vertebrates, ducts are utilized for this purpose. These ducts, together with the structures that serve to bring the gametes of both sexes together, are known as accessory sex organs. The structures used to transport the reproductive cells in the male are known as deferent ducts and those of the female as oviducts. In a few forms no ducts are present in either sex, and eggs and sperm escape from the body cavity through genital or abdominal pores.
Oviducts, except in teleosts and a few other fishes, are modifications of Möllerian ducts formed during early embryonic development. In all mammals, each differentiates into an anterior, nondistensible Fallopian tube and a posterior, expanded uterus. In all mammals except monotremes the uterus leads to a terminal vagina which serves for the reception of the penis of the male during copulation. The lower part, or neck, of the uterus is usually telescoped into the vagina to a slight degree. This portion is referred to as the cervix.
In most vertebrates the reproductive ducts in both sexes open posteriorly into the cloaca. In some, modifications of the cloacal region occur and the ducts open separately to the outside or, in the male, join the excretory ducts to emerge by a common orifice. See also Copulatory organ; Ovary; Penis; Reproduction (animal).
Physiology
The physiological process by which a living being gives rise to another of its kind is considered one of the outstanding characteristics of plants and animals. It is one of the two great drives of all animals; self-preservation and racial perpetuation.
Estrous and menstrual cycles
The cyclic changes of reproductive activities in mammalian females are known as estrous or menstrual cycles.
Most mammalian females accept males only at estrus (heat). Estrus in mammals can occur several times in one breeding season; the mare, ewe, and rat come to estrus every 21, 16, and 5 days respectively if breeding does not take place. This condition is called poly estrus. The bitch is monestrous; she has only one heat, or estrus, to the breeding season and if not served then, she does not come into heat again for a prolonged interval, 4–6 months according to different breeds. In monestrous and seasonally polyestrous species the period of sexual quiescence between seasons is called anestrus. See also Estrus.
The reproductive cycle of the female in the primate and human is well marked by menstruation, the period of vaginal blood flow. Menstruation does not correspond to estrus but occurs between the periods of ovulation at the time the corpus luteum declines precipitously. See also Menstruation.
Mating
Mating, also called copulation or coitus, is the synchronized bodily activity of the two sexes which enables them to deposit their gametes in close contact. It is essential for successful fertilization because sperm and ovum have a very limited life span.
The logistics of sperm transport to the site of fertilization in the oviduct present many interesting features in mammals, but it is important to distinguish between passive transport of sperm cells in the female genital tract, and sperm migration, which clearly attributes significance to the intrinsic motility of the cell. Viable spermatozoa are actively motile, and although myometrial contractions play a major role in sperm transport through the uterus, progressive motility does contribute to migration into and within the oviducts. Even though a specific attractant substance for spermatozoa has not yet been demonstrated to be released from mammalian eggs or their investments, some form of chemotaxis may contribute to the final phase of sperm transport and orientation toward the egg surface.
Although in most mammalian species the oocyte is shed from the Graafian follicle in a condition suitable for fertilization, ejaculated spermatozoa must undergo some form of physiological change in the female reproductive tract before they can penetrate the egg membranes. The interval required for this change varies according to species, and the process is referred to as capacitation. The precise changes that constitute capacitation remain unknown, although there is strong evidence that they are—at least in part—membrane-associated phenomena, particularly in the region of the sperm head, that permit release of the lytic acrosomal enzymes with which the spermatozoon gains access to the vitelline surface of the egg.
Fertilization takes place in the oviducts of mammals and the fertilized eggs or embryos do not descend to the uterus for some 3 to 4 days in most species. During this interval, the embryo undergoes a series of mitotic divisions until it comprises a sphere of 8 or 16 cells and is termed a morula. Formation of a blastocyst occurs when the cells of the morula rearrange themselves around a central, fluid-filled cavity, the blastocoele. As the blactocyst develops within the uterine environment, it sheds its protective coat and undergoes further differentiation before developing an intimate association with the endometrium, which represents the commencement of implantation or nidation.
Association of the embryo with the uterine epithelium, either by superficial attachment or specific embedding in or beneath the endometrium, leads in due course to the formation of a placenta and complete dependence of the differentiating embryo upon metabolic support from the mother. Implantation and placentation exhibit a variety of forms, but in all instances the hormonal status of the mother is of great importance in determining whether or not implantation can proceed. See also Pregnancy.
Endocrine function
The endocrine glands secrete certain substances (hormones) which are necessary for growth, metabolism, reproduction, response to stress, and various other physiological processes. The endocrine glands most concerned with the process of reproduction are the pituitary and the gonads.
The posterior lobe of the pituitary gland secretes two neuro-humoral agents, vasopressin and oxytocin. These are involved in reproduction only indirectly, through their effect on uterine contractility in labor and on the release of milk from the mammary gland when a suckling stimulus is applied. The anterior lobe secretes a variety of trophic hormones, including two gonadotrophic hormones, the follicle-stimulating hormone (FSH) and the luteinizing or interstitial-cell stimulating hormone (LH or ICSH). These hormones act directly on both ovaries and testes. See also Pituitary gland.
The gonadal (steroidal) hormones control the secretion of gonadotrophins by acting on the hypothalamus. It has been suggested that steroids act by means of a “negative feedback”; that is, high levels of circulating gonadal hormones stop further release of gonadotropins. However, although this is true for experiments involving pharmacological doses of such hormones, it may not be the case with endogenous physiological levels. It is certainly true that less steroid is required to inhibit pituitary function in the female than in the male. Under certain circumstances small doses of gonadal hormones can stimulate release of gonadotropic hormones from the pituitary. Estrogen can simulate the release of LH; hence the occurrence of ovulation in rats, rabbits, sheep, and women. Progesterone can also facilitate ovulation in persistently estrous rats, in chickens, and in estrous sheep and monkeys. See also Estrogen; Progesterone.
The formation of gametes (spermatogenesis and oogenesis) is controlled by anterior pituitary hormones. The differentiation of male and female reproductive tracts is influenced, and mating behavior and estrous cycles are controlled, by male or female hormones. The occurrence of the breeding season is mainly dependent upon the activity of the anterior lobe of the pituitary, which is influenced through the nervous system by external factors, such as light and temperature. The transportation of ova from the ovary to the Fallopian tube and their subsequent transportation, development, and implantation in the uterus are controlled by a balanced ratio between estrogen and progesterone. Furthermore, it is known that estrogens, androgens, and progesterone can all have the effect of inhibiting the production or the secretion, or both, of gonadotrophic hormones, permitting the cyclic changes of reproductive activity among different animals.
Mammary glands are essential for the nursing of young. Their growth, differentiation, and secretion of milk, and in fact the whole process of lactation, are controlled by pituitary hormones as well as by estrogen and progesterone. Other glands and physiological activities also influence lactation, although this is largely via the trophic support of other pituitary hormones.
| World of the Body: reproductive system |
The gonads, which produce the GERM CELLS, and all associated organs and tissues in either sex that provide the mechanisms for fertilization and development of an embryo: in the male, the testes, vasa deferentia, prostate, seminal vesicles, and penis; in the female, the ovaries, Fallopian tubes, uterus, vagina, and mammary glands (breasts). Also, in both sexes, the relevant sex hormones and the tissues that produce them.
— Stuart Judge
See urogenital system.
| Britannica Concise Encyclopedia: human reproductive system |
(click to enlarge)
Organs of the human reproductive system. In a male, the scrotum, a pouch of skin, is divided into (credit: © Merriam-Webster Inc.)
Organs of the human reproductive system. In a male, the scrotum, a pouch of skin, is divided into (credit: © Merriam-Webster Inc.)
For more information on human reproductive system, visit Britannica.com.
| Columbia Encyclopedia: reproductive system |
reproductive system, in animals, the anatomical organs concerned with production of offspring. In humans and other mammals the female reproductive system produces the female reproductive cells (the eggs, or ova) and contains an organ in which development of the fetus takes place; the male reproductive system produces the male reproductive cells, the sperm, and contains an organ that deposits the sperm within the female.
In the Human Female
In the human female reproductive system, ova are produced in the ovaries, two small organs set in the pelvic cavity below and to either side of the navel. The ovaries also secrete, in cyclic fashion, the hormones estrogen and progesterone (see menstruation). After an ovum matures, it passes into the uterine tube, or fallopian tube. If sperm are present as a result of sexual intercourse or artificial insemination, fertilization occurs within the tube. The ovum, either fertilized or unfertilized, then passes down the fallopian tube, aided by cilia in the tube, and into the womb, or uterus, a pear-shaped organ specialized for development of a fertilized egg.
An inner uterine layer of tissue, the endometrium, undergoes cyclic changes as a result of the changing levels of the hormones secreted by the ovaries. The endometrium is thickest during the part of the menstrual cycle in which a fertilized ovum would be expected to enter the uterus and is thinnest just after menstruation. If no fertilized egg is present toward the end of the cycle, the thickened endometrium degenerates and sloughs off and menstruation occurs; if a fertilized egg is present it becomes embedded in the endometrium about a week after fertilization. The developing embryo produces trophoblastic cells and these, along with cells from the endometrium, form the placenta, the organ in which gas, food, and waste exchange between mother and embryo takes place. The embryo also forms the amniotic sac within which it develops.
The lower end of the uterus is called the cervix. The vagina, a passage connecting the uterus with the external genitals, receives the penis and the sperm ejaculated from it during sexual intercourse. It also serves as an exit passageway for menstrual blood and for the baby during birth. The external genitals, or vulva, include the clitoris, erectile tissue that responds to sexual stimulation, and the labia, which are composed of elongated folds of skin. After birth the infant is fed with milk from the breasts, or mammary glands, which are also sometimes considered part of the reproductive system.
In the Human Male
In the male reproductive system sperm are produced in the seminiferous tubules of the testes, two organs contained in the scrotum, an external sac in the groin. The testes also produce the male hormone testosterone and a portion of the seminal fluid, the liquid in which sperm are carried. The external location of the scrotum ensures the relatively low temperature that is necessary for the normal development of sperm. After formation, the sperm pass from the testes into the tubular epididymis, and from there into another passage, the vas deferens. The seminal vesicle, which produces nutrient seminal fluid, and the prostate gland, which produces alkaline prostatic fluid, are both connected to the ejaculatory duct leading into the urethra.
The first stage of the male sexual act, erection, results from nerve impulses from the autonomic nervous system that dilate the arteries of the penis, thus allowing arterial blood to flow into erectile tissues of the organ. During intercourse, contractions in the ducts of the testes, epididymis, and ductus deferens cause expulsion of sperm into the urethra and their mixture with the seminal and prostatic fluids. These substances, together with mucus secreted by accessory glands known as Cowper's glands, form the semen, which is discharged from the penile urethra during ejaculation.
Human Reproductive Disorders
Disorders that may affect the proper functioning of the reproductive system include abnormal hormone secretion, sexually transmitted diseases, and the presence of cancerous tissue in the region. Such problems frequently affect fertility and may complicate pregnancy.
See infertility. See also fertility drug; in vitro fertilization.
| Health Dictionary: reproductive systems |
The organs and glands in the body that aid in the production of new individuals (reproduction). (See illustrations below and next page.)
In the male, sperm are produced in the testes and conveyed to the female in a fluid called semen, which passes out of the body through the penis. Other parts of the male reproductive system include the prostate gland, the scrotum, and the urethra.
In the female, the eggs, or ova are produced in the ovaries and released during ovulation into the fallopian tubes about halfway through the menstrual cycle. If fertilization occurs, the resulting zygote travels down the fallopian tube to the uterus, where it implants and continues development. If the ovum is not fertilized, it continues its journey toward the uterus, where it degenerates and is released in the menstrual flow through the vagina during menstruation.
| Wikipedia: Reproductive system |
This article is about sexual reproductive systems. For the reproductive systems of asexual organisms, see Asexual reproduction.
The reproductive system is a system of organs within an organism which work together for the purpose of 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]
The major organs of the human 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.
Contents |
Human reproductive system
Further information: Human reproduction
Human reproduction takes place as internal fertilization by sexual intercourse. During this process, the erect penis of the male is inserted into the female's vagina until the male ejaculates semen, which contains sperm, into the female's vagina. 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 foetus 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. 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]
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.
Male reproductive system
Main article: Male reproductive system (human)
The human 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 reproductive process. The primary direct function of the male reproductive system is to provide the male gamete or spermatozoa 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 female, these include the penis, urethra, vas deferens, and Cowper's gland.
Major secondary sexual characteristics include: 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.[5]
Female reproductive system
Main article: Female reproductive system (human)
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 vagina, which acts as the receptacle for the male's sperm, the uterus, which holds the developing fetus, and the ovaries, which produce the female's ova. The breasts are also an important reproductive organ during the parenting stage of reproduction.
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. At certain intervals, typically approximately every 28 days, the ovaries release an ovum, which passes through the fallopian tube into the uterus. The lining of the uterus, called the endometrium, and unfertilized ova are shed each cycle through a process known as menstruation.
Major secondary sexual characteristics include: a smaller stature, a high percentage of body fat, wider hips, development of mammary glands, and enlargement of breasts. Important sexual hormones of females include estrogen and progesterone.[5]
Production of gametes
Main articles: Spermatogenesis and Oogenesis
The production of gametes takes place within the gonads through a process known as gametogenesis. Gametogenesis occurs when certain types of germ cells undergo meiosis to split the normal diploid number of chromosomes in humans (n=46) into haploids cells containing only 23 chromosomes.[6]
In males this process is known as spermatogenesis and takes place only after puberty in the seminiferous tubules of the testes. The immature spermatozoon or sperm are then sent to the epididymis where they gain a tail and motility. Each of the original diploid germs cells or primary spermatocytes forms four functional gametes which is each capable of fertilization.
In females gametogenesis is known as oogenesis which occurs in the ovarian 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 primary oocytes will form only one mature ovum, and three polar bodies which are not capable of fertilization.
It has long been understood that in females, unlike males, all of 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.[6] However, recent scientific data has challenged that hypothesis.[7] This new data indicates that in at least some species of mammal oocytes continue to be replenished in females well after birth. [8]
Development of the reproductive system
Main article: Development of the urinary and reproductive organs
The development of the reproductive system and urinary systems are closely tied in the development of the human fetus. Despite the differences between the adult male and female reproductive system, there are a number of homologous structures shared between them due to their common origins within the fetus. Both organ systems are derived from the intermediate mesoderm. The three main fetal precursors of the reproductive organs are the Wolffian duct, Müllerian ducts, and the gonad. Endocrine hormones are a well known and critical controlling factor in the normal differentiation of the reproductive system.[9]
The Wolffian duct forms the epididymis, vas deferns, ductus deferens, ejaculatory duct, and seminal vesicle in the male reproductive system and essentially disappears in the female reproductive system. For the Müllerian Duct this process is reversed 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 gonad goes on to form the testes and ovaries, because they are derived from the same undeveloped structure they are considered homologous 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 rather analogous structures as they arise from different fetal structures.
| Male organ | Female organ | Shared function |
|---|---|---|
| Cowper's gland | Bartholin's glands | Lubrication secretions |
| Penis | Clitoris | Erectile tissue and sensation |
| Testes | Ovary | Gamete production |
| Prostate gland | Skene's gland | Ejaculatory fluid and sensation |
Diseases of the human reproductive system
Main article: Reproductive system disease
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: 1) genetic or congenital abnormalities, 2) cancers, 3) infections which are often sexually transmitted diseases, and 4) functional problems cause by environmental factors, physical damage, psychological issues, autoimmune disorders, or other causes. The best known type of functional problems include sexual dysfunction and infertility which are both broad terms relating to many disorders with many causes.
Specific reproductive diseases are often symptoms of other diseases and disorders, or have multiple, or unknown causes making them difficult to classify. Examples of unclassifiable disorders include Peyronie's disease in males and endometriosis in females. Many congenial conditions cause reproductive abnormalities but are better known for their other symptoms, these include: Turner syndrome, Klinefelter syndrome, Cystic fibrosis, and Bloom syndrome.[10]
It is also known that disruption of the endocrine system by certain chemical adversely affects the development of the reproductive system and can cause vaginal cancer.[11] Many other reproductive diseases have also been link to exposure to synthetic and environmental chemicals. Common chemicals with known links to reproductive disorders include: lead, dioxin, styrene, toluene, and pesticides.[12]
Examples of congenital abnormalities
- Kallmann syndrome - Genetic disorder causing decreased functioning of the sex hormone-producing glands caused by a deficiency of a hormone.
- Cryptorchidism - Absence of one or both testes from the scrotum.
- Androgen insensitivity syndrome - A genetic disorder causing people who are genetically male (i.e. XY chromosome pair) to develop sexually as a female due to an inability to utilize androgen.
- Intersexuality - A person who has genitalia and/or other sexual traits which are not clearly male or female.
Examples of cancers
- Prostate cancer - Cancer of the prostate gland.
- Breast cancer - Cancer of the mammary gland.
- Ovarian cancer - Cancer of the ovary.
- Penile cancer - Cancer of penis.
- Uterine cancer - Cancer of the uterus.
- Testicular cancer - Cancer of the testicles.
- Cervical Cancer - Cancer of the cervix.
Examples of infections
- HIV - Infection by the retrovirus known as human immunodeficiency virus.
- Genital warts - Sexually transmitted infection caused by some sub-types of human papillomavirus (HPV).
- Herpes simplex - Sexually transmitted infection caused by a virus called herpes simplex virus (HSV) type 2
- Gonorrhea - Common sexually transmitted disease caused by the Gram-negative bacterium Neisseria gonorrheae
- Yeast infection - Infection of the vagina by any species of the fungus genus Candida.
- Pelvic inflammatory disease - Painful infection of the female uterus, fallopian tubes, and/or ovaries with associated scar formation and adhesions to nearby tissues and organs.
- Syphilis - Sexually transmitted infection caused by the bacterium Treponema pallidum.
- Pubic lice - Infection of the pubic hair by crab lice, Phthirius pubis.
- Trichomoniasis - Sexually transmitted infection by the single-celled protozoan parasite Trichomonas vaginalis.
Examples of functional problems
- Impotence - The inability of a male to produce or maintain an erection.
- Hypogonadism - A lack of function of the gonads, in regards to either hormones or gamete production.
- Ectopic pregnancy - When a fertilized ovum is implanted in any tissue other than the uterine wall.
- Hypoactive sexual desire disorder - A low level of sexual desire and interest.
- Female sexual arousal disorder - A condition of decreased, insufficient, or absent lubrication in females during sexual activity
- Premature ejaculation - A lack of voluntary control over ejaculation.
Other vertebrates
See also: Sexual reproduction
Vertebrate animals all share key elements of their reproductive systems. They all have gamete producing organs or gonads. These gonads are then connected by oviducts to an opening to the outside of the body, typically the cloaca, but sometime to a unique pore such as a vagina or intromittent organ.
Mammals
Most mammal reproductive systems are similar, however, there are some notable differences between the "normal" mammal and humans. For instance, most mammalian males have a penis which is stored internally until erect, and most have a penis bone or baculum. 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.[13][14]
Marsupials are 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. 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.[15]
The uterus and vagina are unique to mammals with no homologue in birds, reptiles, amphibians, or fish.[16] 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.
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 the "cloacal kiss", during which time the male transfers his sperm to the female. A few species of birds (e.g. most waterfowl) have a intromittent organ which is known as a phallus that is analogous to the mammals' penis. The female lays amniotic eggs in which the young gestate. Unlike most vertebrates female birds typically have only one functional ovary and oviduct.[17] 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 viviparous (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.
Amphibians
Most amphibians exhibit external fertilization of eggs, typically within the water, though some amphibians such as caecilians have internal fertilization.[18] All have paired, internal gonads, connected by ducts to the cloaca.
Fish
Main article: Fish#Reproductive_method
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 a large quantities 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.[19] A small portion of fish species are either viviparous or ovoviviparous, and are collectively known as livebearers.[20]
Fish gonads are typically pairs of either ovaries or testes. Most fish are sexually dimorphic but some species are hermaphroditic or unisexual.[21]
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.[22] Likewise, male cephalopods have only a single teste. 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 transfers the spermatophores directly to the female.
Many cephalopods shed their gonads during reproduction, and thus only reproduce once. Most cephalopods die after reproducing. Females nautilus however, have the ability to regenerate their gonads, making them the only cephalopods to spawn once per year. The females in many cephalopod species exhibit some level of parental protection for their eggs.
See also
- Major systems of the human body
- Reproductive system disease
- Sexual reproduction
- Human sexuality
- Human sexual behavior
- Sex organ
- Plant sexuality
References
- ^ Introduction to the Reproductive System. SEER's Training Website. U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program.
- ^ Reproductive System 2001 Body Guide powered by Adam
- ^ STD's Today National Prevention Network, Center for Disease Control, United States Government, retrieving 2007
- ^ Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.
- ^ a b Hormones of the Reproductive System 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.
- ^ a b Development of sex cells in Reproductive system, Body Guide. Adam.
- ^ Tilly JL, Niikura Y, Rueda BR (August 2008). "The Current Status of Evidence for and Against Postnatal Oogenesis in Mammals: A Case of Ovarian Optimism Versus Pessimism?". Biol. Reprod. 80: 2. doi:. PMID 18753611.
- ^ Johnson J, Canning J, Kaneko T, Pru JK, Tilly JL (March 2004). "Germline stem cells and follicular renewal in the postnatal mammalian ovary". Nature 428 (6979): 145–50. doi:. PMID 15014492.
- ^ [http://www.epa.gov/endocrine/inventory/RTD-KELC.html EDRI Federal Project Inventory: Cellular and Molecular Mechanisms of Abnormal Reproductive Development] US EPA. Dr. William R. Kelce. 2006.
- ^ Genetic Conditions > Reproductive system. 2007. Genetics Home Reference. U.S. National Library of Medicine.
- ^ "Endocrine Disruptors" (PDF). National Institute of Environmental Health Sciences. 2006. http://www.niehs.nih.gov/health/topics/agents/endocrine/docs/endocrine.pdf. Retrieved 2007-11-29.
- ^ Infertility and Related Reproductive Disorders. 2003. Ted Schettler, MD. The collaborative on health and the environment.
- ^ 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:. PMID 9892556.
- ^ Descent of the testicles. P.Z. Myers. Pharyngula blog. 2004.
- ^ Renfree, Marilyn; Tyndale-Biscoe, C. H. (1987). Reproductive physiology of marsupials. Cambridge, UK: Cambridge University Press. ISBN 0-521-33792-5. http://books.google.com/books?id=HpjovN0vXW4C&pg=PA129&lpg=PA129&dq=marsupial+scrotum&source=web&ots=9mQ7K3OvQC&sig=pz9pr4gKpbeJ4eSRjHjejwF_Sdo.
- ^ Evolution of the mammalian vagina. P.Z. Myers. Pharyngula blog. Tuesday, November 01, 2005.
- ^ Avian Reproduction: Anatomy & the Bird Egg Gary 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. p. 301–302.
- ^ Fish Reproduction
- ^ Science, Biology, and Terminology of Fish reproduction: Reproductive modes and strategies-part 1. 2002. MARTIN MOE. THE BREEDER'S NET Online Magazine
- ^ Bony Fish Reproduction 2002. SeaWorld/Busch Gardens Animal Information Database.
- ^ Cephalopods. The Living World of Molluscs. Robert Nordsieck.
|
|||||
|
||||||||||||||||||||||||||||
|
||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Learn More
 | urogenital system |
| Mehlis gland |
| genital tract (anatomy) |
 | Are the Human reproductive system same as the Mammal reproductive system? Read answer... |
| How do the circulatory and reproductive systems work in conjuction in reproductive system? Read answer... |
| Does a bisexual flower have one reproductive system or both reproductive systems? Read answer... |
Help us answer these
 | Which system is related to the reproductive system? |
| What does the reproduction system do? |
| Immune system and reproductive system? |
Post a question - any question - to the WikiAnswers community:
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
 |
| World of the Body. The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved. Read more |
 |
| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
 |
| Health Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
 |
| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Reproductive system". Read more |
Related answers
- What is the reproductive system?
- What systems work with the reproduction system?
- What is the job of the reproductive system?
Answer these
- What is the reproduction system?
- What does the reproductive system?
- What does the reproductive system do?
Mentioned in
- Mehlis gland
- genital tract (anatomy)
- Prostate gland (in medicine)
- What is the function of the reproductive system? (anatomy)
- Is the reproductive system essential for life? (anatomy)
- Which branch of medicine specializes in the reproductive system? (anatomy)
- dart sac (invertebrate zoology)
- pyosalpinx (medicine)
- Gynecologist (in medicine)
- Somatization disorder (in medicine)
- Testicles (in medicine)
- What are the organs of the reproductive system and their general function? (anatomy)
- nongonococcal urethritis
- uterus (Health)
