Placenta Question

[justadream]

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Isn’t the placenta partially derived from the fetus/zygote (the trophoblast) and partially derived from the mother’s endometrium?



If so, why is “endometrium” an INCORRECT response to the following TPR question:



“A radioactive dye is detected only in the cells of the placenta villi. Weeks earlier, it must have been injected into the ____”?



The correct answer is “trophoblast” which I agree with – but why can’t “endometrium” work as well?

 

[Cawolf]

I am no expert on embryology - but a quick look in my book gives me one explanation.

The villi are formed from the chorion and then enter the endometrium. Since these structures are derived purely from the trophoblast, and the dye is only in the villi, then the dye must have been injected into the trophoblast.

 

[justadream]

@Cawolf

Okay thanks for that response! I went with trophoblast too but then I started thinking about the properties of the dye (e.g., is it hydrophobic? can it diffuse through the membranes, etc).