Reproduction is creation of new individuals belonging to the same species. Though reproduction is not necessary to maintain life of an individual but maintains the species or population . Reproduction can be said to involve making copies of blue prints of body design. The basic event in the reproduction is the creation of DNA copy.
For cellular organisms, cell division or fission, leads to formation of new individuals. Fission can be binary if forming only two daughter individuals e.g., Amoeba, Paramecium otherwise if divide into many daughter cells simultaneously, it is called multiple fission e.g., Plasmodium. Binary fission can occur in any plane e.g., Amoeba or in a definite orientation in relation to their structures.
This is not true for multicellular organisms which need to use more complex ways of reproduction. Some organisms like Hydra can use regenerative cells for reproduction in the process of budding. A bud develops as a small outgrowth and can develop into small individual which when fully mature, get separated from the parent body and become new individual. This type of reproduction is called asexual reproduction and a single parent is involved.
Other mode of reproduction is called sexual reproduction. It involves participation of both, male and female sexes. Human use a sexual mode of reproduction only.
Human Reproductive System
|1.||Male reproductive system: It consists of 2 parts|
- Portion which produce the germ cells/spermatozoa (Testes)
- Portion which deliver spermatozoa to the site of fertilization.
A pair of testes are located in the scrotal sac, outside the abdominal cavity. This is to provide optimum temperature for the formation of spermatozoa which is slightly lower than the body temperature. Besides, testes are also an endocrine structure releasing testosterone. Testosterone is involved in appearance of secondary sexual characters and also, regulates formation of sperms.
The sperms from the testes pass through vas deferens. Both vasa deferentia combine with each other and also with a tube coming from the urinary bladder to form urethra. Thus, urethra is a common passage for sperms and urine. Along the path of vas deference secretion from seminal vesicle and prostate gland gets added forming the semen. As the sperms are now in a fluid, this makes their transport easier. The semen also contains fructose to provide energy. The sperms are the flagellated structure having a long tail. This helps them to move towards germ cell or ovum.
|2.||Female reproductive system: Female reproductive system has a pair of ovary for producing germ cells/eggs/ova. Besides, ovary also produce oestrogen hormone responsible for development of secondary sexual characters at puberty. At the time of birth, ovaries already contain thousands of immature eggs. Maturation of some eggs starts phase-wise on attaining puberty. One egg is produced every month by one of the ovaries. From the ovary, ovulation or release of ovum occurs which enters the thin oviduct/fallopian tube. Both the oviduct open into womb/uterus, which is an elastic bag like structure. The uterus open through the cervix into the vagina.|
|3.||Fertilization and development: During sexual intercourse, the spermatozoa are released into vagina and from these, these move upward and reach the fallopian tube. The sperms encounter ova in the fallopian tube and fertilization occurs forming the zygote. Zygote starts dividing (cleavage) and also move towards uterus to get implanted in the lining of uterus. Rest of development of embryo/foetus occurs in uterus. The embryo gets nourishment from the maternal blood with the help of a special tissue called placenta. The waste generated by developing embryo also gets removed through placenta into mothers blood. The development of child inside the mother's body takes approximately nine months (Gestation period). The child is born as a result of rhythmic contraction of the muscles in the uterus.|
If the eggs is not fertilized, it survives for about 24 hours. As one ovum is released each month by ovary, the uterus also prepared itself each month to receive a fertilized egg. Uterus gets prepared by making its lining thick, spongy and highly vascular. If implantation fails, the thick lining of uterus is also lost and comes out through the vagina as blood and cells. This is called menstruation. It usually lasts for 2-8 days and also takes place roughly every month.
As sexual act is very intimate contact between the bodies, a number of disease can get transmitted sexually like gonorrhoea, syphilis, warts, HIV-AIDS (sexually transmitted disease). The transmission can be prevented to certain extent by using condom which is a covering for penis.
Contraceptive methods: Many ways have been devised to avoid pregnancy during sexual contact. These can be
- Mechanical barrier: These prevent the contact between sperm and ova. Condoms on the penis or female condom worn in vagina.
- Hormonal methods: By changing the hormonal balance which prevents release of egg fertilization. These can have side effects also.
- Intra-uterine devices (IUD): These are placed in the uterus e.g., Loop or Copper T.
- Surgical approach: By blocking the vas deferens in male or fallopian tube in female. This method is safe in the long run.
Surgical methods can be used for removal of unwanted pregnancies (Medical Termination of Pregnancy-MTP). This may be misused for female foeticide. Because of reckless female foeticides, child sex ratio is declining at an alarming rate. For that reason prenatal sex determination has been prohibited by law. For a healthy society the female-male sex ratio must be maintained.