Human Reproductive system
18. Human Body - Reproductive system
Reproductive system
Life could not exist without reproduction. This does not mean that all species reproduce in the same way. Humans reproduce slightly differently from other species and are even capable of controlling reproduction. There are two types of reproduction viz. asexual reproduction and sexual reproduction. Sexual reproduction produces offspring that are genetically different from their parents. Asexual reproduction produces offspring genetically identical to their parent. These offspring are produced by mitosis.
1) Fission : A unicellular organisms such as paramaecium, amoeba split into two cells (binary fission) that are similar to the parent cell whereas plasmodium undergo multiple fission to produce many daughter cells.
1) Fission : A unicellular organisms such as paramaecium, amoeba split into two cells (binary fission) that are similar to the parent cell whereas plasmodium undergo multiple fission to produce many daughter cells.
2) Budding: In this process an offspring grows out of the body of the parent e.g. Hydra
4) Fragmentation: In this form, the body of the parent breaks into distinct pieces, each of which can produce an offspring. Planariansexhibit this type of reproduction.
5) Regeneration: In this form, if a piece of a parent is detached, it can grow and develop into a completely new individual.Echinoderms & Crustaceans exhibit this type of reproduction.
Sexual reproduction
In sexual reproduction new individuals are produced by the fusion of haploid gametes to form a diploid zygote. Sperm are malegametes, egg or ova (ovum singular) are female gametes. Meiosis is a type of cell division that produces cells with half number of chromosomes of the original cell(haploid). Fertilization is the fusion of two such distinctive cells that produces a unique new combination of alleles. Thus Zygote has the full number of chromosomes typical of the species.
In sexual reproduction new individuals are produced by the fusion of haploid gametes to form a diploid zygote. Sperm are malegametes, egg or ova (ovum singular) are female gametes. Meiosis is a type of cell division that produces cells with half number of chromosomes of the original cell(haploid). Fertilization is the fusion of two such distinctive cells that produces a unique new combination of alleles. Thus Zygote has the full number of chromosomes typical of the species.
Male reproductive system
These are the testicles; duct system, including the epididymis and vas deferens; accessory glands; and penis. The two testicles, or testes, produce and store the tiny sperm cells. The counterpart of the ovaries in the female, the testicles are oval shaped and grow to be about 1 inch long. The testicles also produce hormones, including testosterone, which stimulates the production of sperm and facilitates male maturation.
The duct system includes the epididymis and the vas deferens, a muscular tube that passes upward alongside the testes and transports the sperm-containing fluid called semen. Each epididymis is a set of coiled tubes that lies against the testes, connecting them with the vas deferens. With the testes, they hang in a pouchlike structure behind the penis called the scrotum.
The accessory glands, including the seminal vesicles and the prostate gland, provide fluids that lubricate the duct system and nourish the sperm. The seminal vesicles are saclike structures attached to the vas deferens to the side of the bladder. The prostate gland, which produces some of the components of semen, surrounds the ejaculatory ducts at the base of the urethra, just below the bladder. The urethra carries the semen through the penis, a cylindrical structure located between the legs, to the outside. The urethra also discharges urine, which is filtered in the kidneys and stored in the bladder.
The duct system includes the epididymis and the vas deferens, a muscular tube that passes upward alongside the testes and transports the sperm-containing fluid called semen. Each epididymis is a set of coiled tubes that lies against the testes, connecting them with the vas deferens. With the testes, they hang in a pouchlike structure behind the penis called the scrotum.
The accessory glands, including the seminal vesicles and the prostate gland, provide fluids that lubricate the duct system and nourish the sperm. The seminal vesicles are saclike structures attached to the vas deferens to the side of the bladder. The prostate gland, which produces some of the components of semen, surrounds the ejaculatory ducts at the base of the urethra, just below the bladder. The urethra carries the semen through the penis, a cylindrical structure located between the legs, to the outside. The urethra also discharges urine, which is filtered in the kidneys and stored in the bladder.
Female reproductive system
A females internal reproductive organs are the vagina, uterus, fallopian tubes, and ovaries. The main function of this system is to produce eggs, protect and nourish fertilized egg and give birth to offspring. The vagina is a muscular, hollow tube that extends from the vaginal opening to the uterus. The fallopian tubes connect the uterus to the ovaries. They produce, store, and release eggs into the fallopian tubes in the process called ovulation. An ovary sends a tiny egg into one of the fallopian tubes. Unless the egg is fertilized by a sperm while in the fallopian tube, the egg dries up and leaves the body about 2 weeks later through the uterus. This process is called menstruation. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.
During sexual intercourse, semen containing millions of sperms discharges into vagina. The sperms swim up to the fallopian tube and only one sperm fuses with the ovum to produce zygote. The embryo is formed from this zygote.
During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus floats in amniotic fluid inside the amniotic sac. The fetus receives oxygen and nourishment from the mothers blood via the placenta. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mothers body.
Pregnancy lasts an average of 280 days - about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. The mucus that has formed a plug in the cervix loosens, and with amniotic fluid, comes out through the vagina when the mothers water breaks.
When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin.The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The babys head usually comes first; the umbilical cord comes out with the baby and is cut after the baby is delivered. The last stage of the birth process involves the delivery of the placenta, which is now called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.
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