Question

In the simplest type of placenta, six barriers separate maternal blood from foetal blood. How many barriers are lost in human placenta?
A. One
B. Two
C. Three
D. Four

Answer 1

The placenta is an organ that develops in the uterus during pregnancy. This structure provides nutrients and oxygen to the growing baby. It is connected through the umbilical cord with the baby.

Complete Answer:
The placenta with the six layers is known as epithelio- chorial placenta. It is the primitive type and is found in marsupials, lemurs, horse, cow etc.
It is formed by six layers:
(I) Endothelium of maternal blood vessels.
(II) Endometrial connective tissue or mesenchyme.
(III) Uterine epithelium.
(IV) Chorionic epithelium.
(V) Fetal mesenchymal.
(VI) The endothelium of foetal blood vessels.
It has an immediate contact of the two halves of the placenta. The villi of epithelio-chorial placenta push in the wall of the uterus and lie in pockets- like depressions of the uterine wall.
In the human placenta, there are three layers of fetal extraembryonic membrane. It is called the chorio- allantoic placenta. The outermost fetal membrane is derived from trophoblast uterine epithelium; uterine connective tissue and endothelium of maternal blood vessels are not present.

Hence the correct answer is (C). Three layers of barrier are absent in human placenta.

Note: All the mammals almost have a common structure and function of placenta. The difference lies in the gross shape of placenta and the distribution of contact sites between fetal membrane and endometrium. The number of tissues between the maternal and fetal vascular systems also vary a little.