Tuesday, May 16, 2006

COMPARISON BETWEEN THE PLACENTAL AND MARSUPIAL MODE OF REPRODUCTION

The strongly difference between the marsupial and placental mammals is the rate of gestation or time taken by offspring in the uterus. Marsupials and placental mammals differ powerfully in their reproductive anatomy and pattern.

In Marsupials the developing embryo is separated from the body of its mother by amniotic membrane. Subsequent fertilization the embryo develops into a new organism. The immune system of the mother will attack it. The amniotic membrane of the mother separates the embryo from biological interaction with the parent. As there will be the boundary the nutrients will not cross from the mother to the embryo. In marsupial the birth occur earlier than in placental mammals and almost helpless fetus journeys to the pouch and become teat for a week or months depending on the species. Marsupials may stay approximately twelve days within the reproductive tract.

In placenta is composed of several layers which are richly supplied with blood vessels. And act as a barrier to allow nutrients to pass through and preventing the transfer of immune system. In Marsupial pregnancy does not interrupt the progress of the next oestrus cycles as it is interrupted in placental. However ovarian inhibition is mediated by lactation or suckling stimulus. The regulatory alteration is necessary as the baby is no longer carried internally; therefore negative feedback stimulus from the presence of the babies must come nursing from activity instead.

Marsupial and placental mammals differ strongly in their reproductive anatomy and patterns. The reproductive tracts of marsupials are fully doubled. The right and left vaginae do not fuse to form a single body and birth take place through a new median canal called pseudovaginal canal. Right and left uteri are also unfused. Placental mammals do fuse. The right and left uterus do not fuse. The arrangement of ducts that become female reproductive tract do marsupial differ with that of placental mammals. In some marsupials female develop a pouch and it used as a place of are nursed. In males penis is double. The scrotum lies in front of the penis in Marsupial and in the placental scrotum are on the posterior of the penis.

The majority of marsupial gestation period is short. It does not make much contribution to the child. Placental mammals nourished the developing embryo using the mother blood supply, allowing longer gestation. Marsupial has remarkable natural variation that is found among the gestation rates. The wide succession that occurs in the ovary and the genital tract of marsupial are the same but the general timing of events in the reproductive cycles is different from marsupial and even between species and subspecies for instance kangaroo differ from basic marsupial pattern in that gestation and is extended from half to occupy almost all of the oestrus cycle and the difference also exists between red and grey kangaroo. There is appears to be significant variability related to placental development. The placental develop from maternal and embryo tissue, and lifestyle difference between species various species appears to effect the specific of the complex. Different species among the placental may can take different form of placenta. These include change in degree of contact and number of layers of tissue between tissue maternal blood supplies

The mode of reproduction is very complex in marsupial than in placental mammals. The period of gestation is short comparing to the gestation period of placentals. In marsupials reproductive tracts of marsupials are fully doubled and the embryo is separated from the mother. The embryo of placental mammals is attached to the mother.

References

Wikipedia contributors. Placenta wikipedia The free Encyclopedia [internet], 2005 May 08, 15:02 UTC [Cited 2006 may 11]Available from http://en.wikipedia.org//wiki/placenta

Wikipedia contributors. Marsupials wikipedia, The free Encyclopedia [internet], 2005 May 08, 15:02 UTC [Cited 2006 may 11] Available from http://en.wikipedia.org/wiki/placenta
Masiya Kedibone
CSIR PTA
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Cell No:0732519071
Tel No:0128412123
Fax:0128423676
E-mail:kmasiya@csir.co.za

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