The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical sex organs involved in sexual reproduction. Many non-living substances such as fluids, , and are also important accessories to the reproductive system.[ Introduction to the Reproductive System, Epidemiology and End Results (Seer) Program. ] Unlike most , the 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 genes fitness of the offspring.[ Reproductive System 2001 Body Guide powered by Adam]
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
(testicles and ovaries). Diseases of the human reproductive system are very common and widespread, particularly communicable sexually transmitted infections.
[ STD's Today National Prevention Network, Center for Disease Control, United States Government, retrieving 2007]
Most other have similar reproductive systems consisting of gonads, ducts, and openings. However, there is a great diversity of physical as well as Reproduction in every group of vertebrates.
Vertebrates
share key elements of their reproductive systems. They all have gamete-producing organs known as
. In females, these gonads are then connected by
to an opening to the outside of the body, typically the cloaca, but sometimes to a unique pore such as a
vagina.
Humans
The human reproductive system usually involves internal fertilization by sexual intercourse. During this process, the male inserts their
erect penis into the
female's
vagina and
semen, which contains
sperm. The sperm then travels through the vagina and cervix into the
uterus or
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
childbirth, delivery following
Childbirth. Labor consists of the
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
in the female
to
lactation the baby.
[ Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.]
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.
Male
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 , which are housed in the temperature regulating scrotum, immature sperm then travel to the epididymis for development and storage. The second category is 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 Human penis, urethra, vas deferens, and Cowper's gland.
Major secondary sex characteristics include larger, more muscular stature, deepened voice, facial hair 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.
Female
The human female reproductive system is a series of organs primarily located inside of the body and around the
pelvis 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
Ovary, which produce the female's ova. The
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 ova (singular ovum).
Approximately Menstrual cycle, 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. The ovum will move through her fallopian 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 the endometrium, and unfertilized ova are shed each cycle through the process of menstruation. If the ovum is fertilized by sperm, it will attach to the endometrium and embryonic development will begin.
Other mammals
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
mammal penis which is
Penile sheath, and most have a penis bone or
baculum.
[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.] Additionally, both males and females of most species do not remain continually
sexually fertile as humans do and the females of most mammalian species don't grow permanent
mammaries 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 their
Mammalian kidney.
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 Marsupial penis, which corresponds to the females' two vaginae.
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.[
]
In place of the uterus and vagina, non-mammal 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 ), 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.
Dogs
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.
Horses
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).
Even-toed ungulates
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 an intromittent organ which is known as a phallus that is
analogous to the
mammal penis. The female lays
amniote 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.
[Ritchison. BIO 554/754 Ornithology. Eastern Kentucky University.] 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
Hemipenis.
Amphibians
Most
exhibit external fertilization of eggs, typically within the water, though some amphibians such as
have internal fertilization.
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
that are modified into an intromittent organ analogous to the human penis.
[ Fish Reproduction] A small portion of fish species are either viviparous or
ovoviviparous, and are collectively known as
.
[ Science, Biology, and Terminology of Fish reproduction: Reproductive modes and strategies-part 1 . 2002. MARTIN MOE. THE BREEDER'S NET Online Magazine]
Fish gonads are typically pairs of either ovaries or testicles. Most fish are sexually dimorphic but some species are hermaphrodite or unisexual.[ Bony Fish Reproduction 2002. SeaWorld/Busch Gardens Animal Information Database.]
Invertebrates
have an extremely diverse array of reproductive systems, the only commonality may be that they all lay eggs. Also, aside from
and
, nearly all other invertebrates are
hermaphroditic and exhibit external fertilization.
Cephalopods
All
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
Ovum found in the female's single
ovary.
[ Cephalopods. The Living World of Molluscs. Robert Nordsieck.] Likewise, male cephalopods have only a single
testicle. In the female of most cephalopods the
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
reproduce
, i.e. by laying
. 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
. At the time of
fertilization, the eggs travel along
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
, 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.
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,
, which are the reproductive structures of
flowering plant, are the most varied physically and show a correspondingly great diversity in methods of reproduction.
Plants that are not flowering plants (
,
,
Marchantiophyta,
,
and
such as
) 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 component and
abiotic interactions.
Fungi
Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms.
[Alexopoulos et al., pp. 48–56.] 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.
[Kirk et al., p. 633.] 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
.
See also
Cited literature
External links
