Reproductive biology includes both

sexual Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...

and asexual reproduction. Reproductive biology includes a wide number of fields: *

Reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...

s *

Endocrinology Endocrinology (from '' endocrine'' + '' -ology'') is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental event ...

Sexual development Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. I ...

(Puberty) *

Sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...

Reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...

Fertility Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified demographically. Fertili ...

Human reproductive biology

Endocrinology

Human reproductive biology is primarily controlled through

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s, which send signals to the human reproductive structures to influence growth and maturation. These hormones are secreted by

endocrine gland Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid ...

s, and spread to different tissues in the human body. In humans, the

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...

synthesizes hormones used to control the activity of endocrine glands.

Reproductive systems

Internal and external organs are included in the reproductive system. There are two reproductive systems including the male and female, which contain different organs from one another. These systems work together in order to produce offspring.

Female reproductive system

The

female reproductive system The female reproductive system is made up of the internal and external sex organs that function in the reproduction of new offspring. In humans, the female reproductive system is immature at birth and develops to maturity at puberty to be ...

includes the structures involved in ovulation, fertilization, development of an embryo, and birth. Blausen_0400_FemaleReproSystem_02b

These structures include: Male_anatomy_en

Ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

Oviduct The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, o ...

s *

Uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

Vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

Mammary Glands A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in prima ...

Estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

is one of the sexual reproductive hormones that aid in the sexual reproductive system of the female.

Male reproductive system

The

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 tes ...

includes testes, rete testis, efferent ductules, epididymis, sex accessory glands, sex accessory ducts and external genitalia.

Testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

, an androgen, although present in both males and females, is relatively more abundant in males. Testosterone serves as one of the major sexual reproductive

s in the male reproductive system However, the enzyme aromatase is present in testes and capable of synthesizing estrogens from androgens. Estrogens are present in high concentrations in luminal fluids of the male reproductive tract. Androgen and estrogen receptors are abundant in epithelial cells of the male reproductive tract.Zhou, Q., R. Nie, G. S. Prins, P. T. Saunders, B. S. Katzenellenbogen and R. A. Hess (2002). "Localization of androgen and estrogen receptors in adult male mouse reproductive tract." J Androl 23(6): 870-881.

Animal Reproductive Biology

Animal reproduction Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

occurs by two modes of action, including both sexual and asexual reproduction. In

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

the generation of new organisms does not require the fusion sperm with an egg. However, in

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

new organisms are formed by the fusion of haploid sperm and eggs resulting in what is known as the

zygote A zygote (, ) 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 of a new individual organism. In multicellula ...

. Although animals exhibit both sexual and asexual reproduction the vast majority of animals reproduce by sexual reproduction. In many species, relatively little is known about the conditions needed for successful breeding. Such information may be critical to preventing widespread extinction as species are increasingly affected by

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

and other threats. In the case of some species of frogs, such as the Mallorcan midwife toad and the

Kihansi spray toad The Kihansi spray toad (''Nectophrynoides asperginis'') is a small toad endemic to Tanzania.Channing and Howell. (2006). ''Amphibians of East Africa.'' Pp. 106-107. The species is live-bearing and insectivorous. The Kihansi spray toad is curre ...

, it has been possible to repopulate areas where wild populations had been lost.

Gametogenesis

Gametogenesis is the formation of

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s, or reproductive cells.

Spermatogenesis

Spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubule ...

is the production of sperm cells in the testis. In mature testes primordial germ cells divide mitotically to form the spermatogonia, which in turn generate spermatocytes by mitosis. Then each spermatocyte gives rise to four spermatids through meiosis. Spermatids are now haploid and undergo differentiation into sperm cells. Later in reproduction the

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

will fuse with a female

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

to form the zygote.

Oogenesis

Oogenesis Oogenesis, ovogenesis, or oögenesis is the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated in the embryonic stage. O ...

is the formation of a cell who will produce one

ovum The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is ...

and three

polar bodies A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized. It is named from its polar position in the egg. When certain diploid cells in animals ...

. Oogenesis begins in the female embryo with the production of oogonia from primordial germ cells. Like spermatogenesis, the primordial germ cell undergo mitotic division to form the cells that will later undergo meiosis, but will be halted at the prophase I stage. This is known as the primary oocyte. Human females are born with all the primary oocytes they will ever have. Starting at puberty the process of meiosis can complete resulting in the secondary oocyte and the first polar body. The secondary oocyte can later be fertilized with the male sperm.

References

Bibliography

* Lombardi, Julian (1998). ''Comparative Vertebrate Reproduction''. Kluwer Academic Publishers, Boston
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{{Branches of biology Reproduction