reproduction

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reproduction

 [re″pro-duk´shun]
1. the creation of a similar object or situation; replication or duplication.
2. the process by which a living entity or organism produces a new individual of the same kind. The sex glands, or gonads (the ovaries in the female and the testes in the male) produce the germ cells (ova and sperm) that unite and grow into a new individual. Reproduction begins when the germ cells unite, a process called fertilization.
Production of Germ Cells. The germ cells are the male spermatozoon and the female ovum (secondary oocyte). The secondary oocyte (mature ovum) is a large round cell that is just visible to the naked eye. Spermatozoa, on the other hand, can be seen only under a microscope, where each appears as a small, flattened head with a long whiplike tail used for locomotion.



In the female, maturation of an ovum is a remarkable process controlled by hormones secreted by the endocrine glands. The menstrual cycle is ordinarily 28 days long, measured from the beginning of one menstrual period to the beginning of the next. During the first 2 weeks of the usual cycle, one of the ova becomes mature enough to be released from the ovary. At the time of ovulation this mature ovum (secondary oocyte) is released and at this point can be fertilized. If fertilization occurs, the fertilized ovum (zygote) is then discharged into the abdominal cavity. Somehow, by mechanisms that are not clear, it moves into a fallopian tube and begins its descent toward the uterus. If the ovum remains unfertilized, menstrual bleeding occurs about 2 weeks later.

In the male there is no sexual cycle comparable to the cyclical activity of ovulation in the female. Mature sperm are constantly being made in the testes of the adult male and stored there in the duct system.
Fertilization, or Conception. During coitus, semen is ejaculated from the penis into the back of the vagina near the cervix uteri. About a teaspoonful of semen is discharged with each ejaculation, containing several hundred millions of spermatozoa. Of this enormous number of sperm, only one is needed to fertilize the ovum. Yet the obstacles to be overcome are considerable. Many of the sperm are deformed and cannot move. Others are killed by the acid secretions of the vagina (the semen itself is alkaline). The sperm must then swim against the current of secretions flowing out of the uterus.



The sperm swim an average of 0.4 to 2.5 cm (0.1 to 1.0 inch) per minute. When one or more vigorous sperm are able to reach the ovum, which is normally in the outer half of the fallopian tube, fertilization occurs. The head end of the sperm plunges through the thick wall of the ovum, leaving its tail outside. The genetic materials, the chromosomes, are injected into the ovum, where they unite with the chromosomes inherited from the mother (see heredity). The sex of the child is determined at this instant; it depends on the sex chromosome carried by the sperm.

If by chance two ova have been released and are fertilized by two sperm, fraternal (dizygotic) twins are formed. Identical (monozygotic) twins are produced by a single fertilized ovum that divides into two early in its development.
Ovulation and Fertilization. Fertilization typically can occur only (on the average) on 4 days of every menstrual cycle. The mature ovum lives only 1 or 2 days after ovulation, and the sperm have only about the same amount of time before they perish in the female reproductive tract. To fertilize the ovum, coitus must take place within the time that begins 1 or 2 days before ovulation and lasts until 1 or 2 days after ovulation. There is much variation, however, in the time when ovulation occurs. Most women ovulate between 12 and 16 days after the beginning of the last period, but others ovulate as early as 8 or as late as 20 days after the last period began.
Pregnancy. The ovum, now known as a zygote, begins to change immediately after fertilization. The membrane surrounding it becomes impenetrable to other sperm. Soon the zygote is dividing into a cluster of two, then four, then more cells, as it makes its way down the fallopian tube toward the uterus. At first it looks like a bunch of grapes. By the time it reaches the uterus, in 3 to 5 days, the cells are formed in the shape of a minute ball, the blastocyst, which is hollow on the inside with an internal bump at one side where the embryo will form. The blastocyst quickly buries itself in the lining of the uterus (implantation). Occasionally implantation takes place not in the uterine lining, but elsewhere, producing an ectopic pregnancy.



As soon as the blastocyst is implanted, its wall begins to change into a structure that eventually develops into the placenta. Through the placenta the fetus secures nourishment from the mother and rids itself of waste products. Essentially the placenta is a filtering mechanism by which the mother's blood is brought close to the fetal blood without the actual mixing of blood cells.

During the early stages of pregnancy, the fetus grows at an extremely rapid rate. The mother's body must undergo profound changes to support this organism. The muscles of the uterus grow, vaginal secretions change, the blood volume expands, the work of the heart increases, the mother gains weight, the breasts prepare for nursing, and other adjustments are made throughout the mother's body.
Reproduction.
asexual reproduction reproduction without the fusion of germ cells.
assisted reproduction assisted fertility.
cytogenic reproduction production of a new individual from a single germ cell or zygote.
sexual reproduction reproduction by the fusion of female and male germ cells or by the development of an unfertilized ovum.
somatic reproduction production of a new individual from a multicellular fragment by fission or budding.

re·pro·duc·tion

(rē'prō-dŭk'shŭn),
1. The total process by which organisms produce offspring. Synonym(s): generation (1) , procreation
2. The recall and presentation in the mind of the elements of a former impression.
[L. re-, again, + pro-duco, pp. -ductus, to lead forth, produce]

reproduction

/re·pro·duc·tion/ (re″pro-duk´shun)
1. the production of offspring by organized bodies.
2. the creation of a similar object or situation; duplication; replication.reproduc´tive

asexual reproduction  reproduction without the fusion of sexual cells.
cytogenic reproduction  production of a new individual from a single germ cell or zygote.
sexual reproduction  reproduction by the fusion of a female gamete and a male gamete(bisexual r.) or by development of an unfertilized egg (unisexual r.).
somatic reproduction  production of a new individual from a multicellular fragment by fission or budding.

reproduction

(rē′prə-dŭk′shən)
n.
1. The act of reproducing or the condition or process of being reproduced.
2. Biology The sexual or asexual process by which organisms generate new individuals of the same kind; procreation.

reproduction

[rē′prəduk′shən]
Etymology: L, re + producere, to produce
1 the sum of the cellular and genetic phenomena by which organisms produce offspring similar to themselves so that the species is perpetuated. In humans the germ cells, spermatozoa in the male and ova in the female, unite during fertilization to form the new individual. Kinds of reproduction include asexual reproduction, cytogenic reproduction, and sexual reproduction.
2 the creation of a similar structure, situation, or phenomenon; duplication; replication.
3 the recalling of a former idea or impression or of something previously learned. reproductive, adj.

reproduction

Gynecology Conceiving; making babies. See Asexual reproduction, Assisted reproduction, Teratogenicity.

re·pro·duc·tion

(rē'prō-dŭk'shŭn)
1. The recall and presentation in the mind of the elements of a former impression.
2. The total process by which organisms produce offspring.
Synonym(s): generation (1) , procreation.
[L. re-, again, + pro-duco, pp. -ductus, to lead forth, produce]

reproduction

Any process by which an organism gives rise to a new individual. Most biological reproduction is cellular and asexual and occurs by chromosomal duplication followed by elongation and splitting of the cell into two individual cells identical to the parent. Sexual reproduction is more complex and involves the production of specialized body cells called gametes which have experienced two stages of shuffling and redistribution of chromosomal segments and a reduction to half the full number of CHROMOSOMES (haploid). In the fusion of the male and female gametes, sperm and egg respectively (fertilization), the full complement of chromosomes is made up. The potential new individual now has a GENOME different from that of either parent and will differ in many respects. A fertilized ovum divides rapidly and repeatedly, but the reproduced cells do not usually separate, but continue to duplicate and specialize until a new individual is formed. Sometimes, after the first or second division, the reproduced cells separate to form genetically identical siblings.

reproduction

  1. the production of young.
  2. the mechanisms by which organisms give rise to others of the same kind. See SEXUAL REPRODUCTION, ASEXUAL REPRODUCTION.

re·pro·duc·tion

(rē'prō-dŭk'shŭn)
1. The total process by which organisms produce offspring.
2. The recall and presentation in the mind of the elements of a former impression.
[L. re-, again, + pro-duco, pp. -ductus, to lead forth, produce]

reproduction

1. the process by which a living entity or organism produces a new individual of the same kind. It may be asexual or sexual.
2. the creation of a similar object or situation; duplication; replication.
In sexual reproduction the gonads, or sex glands—the ovaries in the female and the testes in the male—produce the germ cells that unite and grow into a new individual. Reproduction begins when the germ cells unite, the process called fertilization.

asexual reproduction
reproduction without the fusion of germ cells; usually by budding or fission.
cytogenic reproduction
production of a new individual from a single germ cell or zygote.
sexual reproduction
reproduction by the fusion of a female germ cell with a male sexual cell or by the development of an unfertilized egg.
somatic reproduction
production of a new individual from a multicellular fragment by fission or budding.
References in classic literature ?
We by no means intend to abolish this personal appropriation of the products of labour, an appropriation that is made for the maintenance and reproduction of human life, and that leaves no surplus wherewith to command the labour of others.
His friend had even hinted at the correct reproduction of his coronet.
Long after Robinson's buggy was out of sight, Martin stood in his doorway and stared at the five handsome figures, spelled out the even more convincing words and admired the excellent reproduction of The First State Bank.
Here," said he, pointing to the picture of an extraordinary flying monster, "is an excellent reproduction of the dimorphodon, or pterodactyl, a flying reptile of the Jurassic period.
She stood in the Square of the Annunziata and saw in the living terra-cotta those divine babies whom no cheap reproduction can ever stale.
And you thought I was the mere stone reproduction of one of them.
Yet, in our experience, the rays or appulses have sufficient force to arrive at the senses, but not enough to reach the quick and compel the reproduction of themselves in speech.
But the completer, the positive, soul, which will merely take [25] that mood into its service (its proper service, as we hold, is in counteraction to the vulgarity of purely positive natures) is also certainly in evidence in Amiel's "Thoughts"--that other, and far stronger person, in the long dialogue; the man, in short, possessed of gifts, not for the renunciation, but for the reception and use, of all that is puissant, goodly, and effective in life, and for the varied and adequate literary reproduction of it; who, under favourable circumstances, or even without them, will become critic, or poet, and in either case a creative force; and if he be religious (as Amiel was deeply religious) will make the most of "evidence," and almost certainly find a Church.
The word is derived from two others: Lua, meaning sun, and ata, meaning variously eggs, life, young, and reproduction.
Lu and lo, Bradley knew to mean man and woman; ata; was employed variously to indicate life, eggs, young, reproduction and kindred subject; cos was a negative; but in combination they were meaningless to the European.
A reproduction of a work of art, by the artist that made
I cannot here enter on the copious details which I have collected on this curious subject; but to show how singular the laws are which determine the reproduction of animals under confinement, I may just mention that carnivorous animals, even from the tropics, breed in this country pretty freely under confinement, with the exception of the plantigrades or bear family; whereas, carnivorous birds, with the rarest exceptions, hardly ever lay fertile eggs.

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