Name:
Location: pretoria, gauteng, South Africa

i completed my Bsc (microbiology physiology) degree in 2005 at University of Limpopo, now im doing my honns in ecological informatics at university of the western cape.

Friday, May 12, 2006

COMPARISON BETWEEN THE PLACENTAL AND MARSUPIAL MODES OF REPRODUCTION

The placenta is a temporary organ which is only present in females especially during pregnancy (gestation) (2). The placenta is composed of two parts the genetically and biological part of the fetus and the other part of the mother. The fetus (baby) is implanted in the wall of the uterus where it receives nutrients and oxygen from the blood of the mother and passes out waste (2). Substances which could be harmful to the baby are filtered out by the placental barrier but some substances are not filtered out like alcohol and chemicals from cigarettes. Some types of viruses can also penetrate the barrier.

Marsupials are mammals in which the female has a pouch (marsupium) in which it rears its young through early infancy. Marsupials differ from placental mammals in their reproductive traits. A marsupial female has two vaginas which both open externally through one orifice (hole) but lead to different compartments within the uterus (1). Males have two penises which correspond to the females two vaginas. Marsupials have a cloaca (posterior opening that serves as the only opening for the intestinal, urinary, and genital tracts) that is connected to an urogenitals sac in both sexes. Marsupials’ males have two prolonged penises which are used to pass only sperm. Waste is stored before expulsion.

A pregnant Marsupial female develops a yolk sack in her womb which delivers nutrients to the embryo. The embryo is born at an early stage of development; it then crawls up into its mothers belly and attaches itself to a nipple. It attaches to the nipple for a number of weeks. Then the offspring passes a stage where it can leave its mothers pouch temporarily and returns for warmth and nourishment (1).

In placental mammals the placenta transfers gases and nutrients and the placenta has metabolic and endocrine (secrete hormones) activity. The placenta produces other hormones, progesterone which is important in maintaining pregnancy and somatomammotropin (placental lactogen). Placental lactogen increases the amount of glucose and lipids in the maternal (mothers) blood and this results in increased sugar levels during pregnancy (2). The placenta is connected to the fetus through the umbilical cord (3) (tube-like structure) which is composed of blood vessels and connective tissue. The placenta is delivered after the delivery of the baby (fetus) (2).

Placental mammals develop a complex placenta to protect the fetus from the mothers immune system and the marsupials do not have to develop a complex fetus. Marsupils give birth earlier than plancental mammals, they do not have to carry a large fetus to full-term. The plancental mammals e.g. humans carry their babies in the placenta for nine months but the marsupial mammals e.g. Kangaroos carry their babies in the placenta for thirty-one to thirty six days(4).
If a placental mammal gives birth early before the time comes (prematurely) the baby is mostly taken care the same way as the marsupial take care of their babies. The baby is wrapped with a blanket on the mothers stomach like a Kangaroo and this method is called the Kangaroo care. Marsupials and mammals take care of their offspring but in different ways.

Reference:

1. Wikipedia contributors. Marsupials [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 17:16. PTA [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Marsupials
2. Wikipedia contributors. Placenta [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 18:21. PTA [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Placenta
3. Wikipedia contributors. Umbilical cord [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 8, 18:02. PTA [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Umbilical_cord
4. Wikipedia contributors. Kangaroo [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 11, 10:30. PTA [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Kangaroo


Lethabo Mosomane
CSIR
Pretoria
0001
Tel: 27 12 841 2133
Fax: 27 12 842 3676
mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

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