Reproductive system is one of the vital organs of body which is associated with the continuance of species. Many non-living fluids, hormones and pheromones are responsible for the success of activity of the reproductive system. Like different organs the sexes of different species are also an important part of reproductive system. The sexes of different species are identified by different characters that make them unique. This sexual dimorphism is responsible for the new genetic combinations as the genetic material of the two individuals is different which results in the offspring’s fitness in the environment. The major human reproductive organs include the external genitalia which comprise the penis and the vulva along with internal organs which include the gamete producing gonads which include testis and ovaries. The diseases of human reproductive system are wide spread and the very common ones are communicable sexually transmitted diseases.
Human reproduction is a very complex process which commences by internal fertilization by sexual intercourse. During the act of sexual intercourse the erect penis of male is inserted into the vagina of the female until male ejaculates semen which contains sperms into the vagina. The sperms introduced into the vagina travel through vagina and cervix and enter the fallopian tube or uterus where they fertilize the ovum. When fertilization is successful then implantation occurs where the foetus gets implanted inside the protective bed of uterus and this duration is termed as pregnancy and its duration is about nine months in human beings. Pregnancy terminates with the birth of the child which occurs by the commencement of labour pains. The process of child birth is called as parturition. During the process of parturition the muscles of uterus and cervix dilate resulting in the coming out of the baby out of the womb of the mother. The human babies are cared by the mother and the father for many years or we can say that parental care reaches zenith in case of humans. One important feature of parental care is presence of mammary glands in females which produce milk for nursing the young ones. Humans have higher level of sexual differentiation. The secondary sexual characteristics also play an important in sexual reproduction in humans.
The male reproductive system in humans consists of a number of organs located externally as well as internally in the pelvic region of male which lead to the successful functioning of male reproductive system. The important function of male reproductive system is to provide the spermatozoa or sperm to be introduced into the vagina of female so as the fertilization of ovum may take place and fertilization may occur resulting in continuation of population. Male reproductive system can be grouped in three categories. First category includes sperm production and storage. Sperms are produced in the testes which remain inside the scrotum from where the sperm moves to the epididymis for maturation and storage. The second category includes the semen producing glands which are the seminal vesicles, prostrate and the vas deferens. The third and the final category include the copulatory organ penis, urethra, vas deferns 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. Important male sexual hormones ate androgens and the testosterone.
The human female reproductive system is also a complex system comprising a number of external and internal organs located in the pelvic region of female body that are responsible for the successful continuation of species. The human female reproductive system consists of three parts. First one is the vagina which receives the sperm from the male during coitus. Second part is the uterus which acts as a protective bed for the developing foetus and the third part are the ovaries which produce ova that are the necessary cells required for the sexual reproduction to achieve success. The mammary glands or the breast form important part of female reproductive system in humans as they provide nourishment to the child after birth by producing milk.
Vagina terminates to outside at the vulva along with labia, clitoris and urethra. During the act of sexual intercourse large amount of mucus is secreted by the Bartholin’s glands and this area is lubricated. The attachment of vagina with uterus is called cervix and the uterus is in turn attached to the ovaries through the fallopian tubes. The ovaries produce a single ovum approximately at an interval of 28 days which passes through the fallopian tube and enters uterus. The lining of the uterus is called as endometrium. If ovum fails to get fertilized it is shed off along with blood capillaries and this process is called as menstruation or funeral of the ovum. The major female secondary sexual characteristics include smaller stature, larger proportion of deposition of body fat, wider hips, and development of mammary glands or breasts. The important female sexual hormones are oestrogen and the progesterone.
The process of production of gametes in the gonads is known as gametogenesis. Gametogenesis is the process in which germ cells undergo meiosis and the number of chromosomes is reduced from diploid to haploid. The number of chromosome in the cells now becomes 23 instead of 46. In males the process of gametogenesis is termed as spermatogenesis occurring only at the onset of puberty in the seminiferous tubules of the testes. The sperm receives its tail and motility in the epididymis. Each diploid germ cell or the primary spermatocyte after meiosis produces four functional haploid gametes capable of carrying out fertilization. In females gametogenesis is called as oogenesis which occurs in the ovarian follicles of the ovaries. Mature ovum is produced only at the time of puberty. As compared to the male primary gametocyte, the female diploid primary gametocyte produces only one functional haploid ovum capable of fertilization and three polar bodies which don’t bear the power of fertilization.
The development of human reproductive system and the urinary system are very closely related in the human foetus. Apart from the differences between the male and female reproductive system there are many homologous structures that lay down the basis for formation of urinary and reproductive system in the human foetus. Both the systems develop from intermediate mesoderm. The three foetal precursors for the reproductive system are the Wolffian duct, Mullerian ducts and the gonads. Hormones secreted by the endocrine glands participate crucially in differentiation of the reproductive system.
The Wolffian duct is responsible for the formation of epididymis, vas deferns, ductus deferens, ejaculatory duct, and seminal vesicle of the human male reproductive system but disappears in the female reproductive system. Mullerian ducts get disappeared in the male reproductive system and they form fallopian tubes, uterus, and vagina. Gonads are responsible for the formation of testes and ovaries and they are derived from the same homologous structures present during the foetal development. There are also other homologous structures present during the development of male and female reproductive system. The fallopian tubes of female and the epididymis along with the vas deferens are analogous structures.
The human reproductive system like other organs is also not free from diseases. These diseases can be grouped under four categories. These include genetic or congenital abnormalities, cancer, infections or sexually transmitted diseases and functional problems caused by environmental factors, physical damage, psychological issues or autoimmune diseases. The best known functional problems of the reproductive system include sterility and sexual dysfunction which later on are responsible for serious disorders. Although there are certain disorders which are still unclassified like the Peyronie’s disease in males and endometriosis in females. The common congenital disorders are the Turner syndrome, Klinefelter’s syndrome, Cystic fibrosis, and Bloom syndrome. The disruption of endocrine system either by environmental factors or by the use of certain drugs badly affect the proper functioning of the reproductive system and may even cause vaginal cancer. Certain chemicals are also responsible for damaging the reproductive system and these chemicals include toluene, lead and pesticides.
The common congenital disorders of the reproductive system include the Kallmann syndrome which is produced by the deficiency of sex hormones resulting in the improper function of sex glands. Cryptorchidism is the condition where either one or both the testes are absent in the scrotum. Androgen insensitivity syndrome is the disorder where the individuals are although genetically males but are sexually females due to inability to utilize androgen. Intersexuality is the condition where an individual has genitalia not clearly differentiated into either of male or female type. Cancers which are most commonly associated with the reproductive system are prostrate cancer, ovarian cancer, breast cancer, cervical cancer, penile cancer, testicular cancer.
The common infections of the reproductive system are HIV infection caused by the retrovirus also known as human immunodeficiency virus. Genital warts are caused by human papillomavirus. Herpes simplex is caused by herpes simplex virus (HSV) type 2. Gonorrhea is caused by Gram-negative bacterium Neisseria gonorrheae. The vaginal infection is caused by certain yeast species specially those belonging to the genus Candida. Painful infection of female uterus, fallopian tubes or ovaries which is associated with scar formation and adhesion of these organs with nearby tissues and organs is called as pelvic inflammatory disease. Syphilis is caused by bacterium Treponema pallidum. Functional problems of the reproductive system include impotence which is found in males only where they lack the ability to maintain or produce erection of penis. Hypogonadism is the condition where gonads are absent. Ectopic pregnancy is the condition where the fertilized ovum gets implanted in other tissue except the uterine wall. Hypoactive sexual desire disorder is the condition where the desire for sex is low.
All vertebrates share common key elements of the reproductive system. All bear gametes producing gonads. The gonads are connected to oviducts which are connected to outside either through cloaca or vagina or an intromittent organ. All mammals generally share the same reproductive system but there are a number of differences between normal mammals and human beings. Like most mammalian males have penis stored internally until it comes in erect position and most bear a penis bone or baculum. Apart from this most male species do not remain continually fertile as humans. Like humans most males have testes descended in the scrotum, some have testes descended on the ventral body wall while others like elephants testes lie undescended deep in the cavities near kidneys. Marsupials are unique mammals where the female has two vaginae both opening externally through one orifice but lead to uterus by different compartments internally. Males also have two penises. The young ones develop in an external pouch which bears teats. Uterus and vagina are unique to mammals. In other vertebrates there is an unmodified oviduct which opens to outside through cloaca. Cloaca acts as an opening for discharge of urine, faeces and gametes.
Male and female birds have a cloaca through which urine, waste material and gametes are passed out. Intercourse is performed by pressing the lips of cloacae together sometimes called as cloacal kiss and during this act the male transfers the sperms into the vagina of the female. In some birds an intromittent organ analogous to the penis of males is present and this organ is known as phallus. After fertilization females lay amniotic eggs in which further development of eggs takes place. Female birds have only single ovary and single oviduct. Birds also show parental care like mammals. Reptiles are sexually dimorphic and show internal fertilization through cloaca. Some reptiles lay eggs while others are viviparous. Reproductive organs are present within the cloaca of reptiles. Most male reptiles have well developed copulatory organs that remain inside the body. Most of the amphibians show external fertilization except the caecilians which exhibit internal fertilization.
Fishes exhibit a wide range of reproductive strategies. Most fishes are oviparous and show external fertilization. Females use their cloaca for releasing their ova called spawn into the surrounding water and males then release milt over these eggs so that they may get fertilized. Some fishes also have intromittent organs comparable to the male penis. Majority of species are dimorphic but some are hermaphrodite also.
We can summarize that reproductive system is a very complex and well beautifully designed system of vertebrates which leads to continuation of species.