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. 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.

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.

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.

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.

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 characteristic of a male genitalia. 1. Testicles, 2. Epididymis, 3. Corpus cavernosa, 4. Foreskin, 5. Frenulum, 6. Urethral opening , 7. Glans penis, 8. Corpus spongiosum, 9. Penis, 10. Scrotum.

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.

Female reproductive system[]

Main article: Female reproductive system (human) The characteristics of the vulva. 1. Pubic hair (shaved), 2.Clitoral hood, 3. Clitoris, 4. Labia majora, 5. Labia minora (enclosing the Vaginal Opening), 6. Perineum.

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.

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.

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. However, recent scientific data has challenged that hypothesis. This new data indicates that in at least some species of mammal oocytes continue to be replenished in females well after birth.

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.

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.