Reproductive system

Reproductive system

Reproductive system
Details
Latin systema reproductionis
Anatomical terminology

The reproductive system or genital system is a system of 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]

Contents

  • Plants 1
  • Fungi 2
  • Animals 3
    • Vertebrates 3.1
      • Humans 3.1.1
        • Male 3.1.1.1
        • Female 3.1.1.2
      • Other mammals 3.1.2
        • Dogs 3.1.2.1
        • Horses 3.1.2.2
      • Birds 3.1.3
      • Reptiles 3.1.4
      • Amphibians 3.1.5
      • Fish 3.1.6
    • Invertebrates 3.2
      • Cephalopods 3.2.1
      • Insects 3.2.2
      • Arachnids 3.2.3
  • See also 4
  • References 5
  • External links 6

Plants

Fungi

Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms.[3]

Animals

In mammals, the major organs of the reproductive system include the external gamete producing gonads (testicles and ovaries). Diseases of the human reproductive system are very common and widespread, particularly communicable sexually transmitted diseases.[4]

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

intromittent organ.

Humans

The 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.[5]

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 secondary sexual characteristics.

Male

The male reproductive system is a series of organs located outside of the body and around the pelvis 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.

Female

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 leads from the vulva, 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. 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

A newborn joey suckles from a teat found within its mother's pouch

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.[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. 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.[7] 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.

Dogs

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.

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).

Birds

Male and female birds have a 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.[8] 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.

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.[9] All have paired, internal gonads, connected by ducts to the cloaca.

Fish

External links

  1. ^ Introduction to the Reproductive System. , Epidemiology and End Results (SEER) Program.
  2. ^ Reproductive System 2001 Body Guide powered by Adam
  3. ^ Alexopoulos et al., pp. 48–56.
  4. ^ STD's Today National Prevention Network, Center for Disease Control, United States Government, retrieving 2007
  5. ^ Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.
  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.  
  7. ^ Renfree, Marilyn; Tyndale-Biscoe, C. H. (1987). Reproductive physiology of marsupials. Cambridge, UK: Cambridge University Press.  
  8. ^ Ritchison. BIO 554/754 Ornithology. Eastern Kentucky University.
  9. ^ Grzimek, B. (1974). Grzimek's Animal Life Encyclopedia: Volume 5 Fishes II & Amphibians. New York: Van Nostrand Reihnhold Co. pp. 301–302.  
  10. ^ Fish Reproduction
  11. ^ Science, Biology, and Terminology of Fish reproduction: Reproductive modes and strategies-part 1. 2002. MARTIN MOE. THE BREEDER'S NET Online Magazine
  12. ^ Bony Fish Reproduction 2002. SeaWorld/Busch Gardens Animal Information Database.
  13. ^ Cephalopods. The Living World of Molluscs. Robert Nordsieck.

References

See also

Arachnids

Insects

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.

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.[13] Likewise, male cephalopods have only a single testicle. In the female of most cephalopods the nidamental glands aid in development of the egg.

Cephalopods

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.

Invertebrates

Fish gonads are typically pairs of either ovaries or testes. Most fish are sexually dimorphic but some species are hermaphroditic or unisexual.[12]

[11].livebearers, and are collectively known as ovoviviparous A small portion of fish species are either viviparous or [10]