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Offline alastair84

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placenta
« on: 14/05/2004 00:54:23 »
Is the placenta derived from the mother or from the embryo?
If it is derived from the embryo, how does it not cause an immune reaction?

-another past exam question haha.


 

Offline Donnah

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Re: placenta
« Reply #1 on: 14/05/2004 01:06:32 »
I'm no expert, but I think it's derived from the mother.  It's there to nourish the baby, so how could it come from the baby?

I remember bovine cesareans where vets pulled the cotyledons off the uterine wall.  Fascinating.  I'd love to see a human c-section.
 

Offline alastair84

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Re: placenta
« Reply #2 on: 14/05/2004 01:42:40 »
saw one on video. The woman was like "is it out yet?" and was so relaxed it was funny.
hmmmm....I just found a little bit in a book, it says the placenta comes from trophoblast cells, which come from the zygote. so i guess this means they're not maternally derived? Can someone definately confirm/disprove this?
 

Offline calcaneus

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Re: placenta
« Reply #3 on: 14/05/2004 02:45:26 »
Placenta is organ derivated partialy from embryonic component, and partialy from endometrium utheri.

Chorion frondosum is fetal component (it proliferates into vili chorioidales).
Decidua basalis is maternal component. It has number of cavities (intervilous spaces) filled with mothers blood.

Embryo with its covering stuctures is geneticly unique foreign body. Immune reaction is not caused because of changed expression of MHC antigens from trophoblast cells.
MHC antigens are superficial molecules. Identified by T-lymfocites, forein cells with MHC antigens are being destroyed.
That is why trophoblast cells DO NOT produce MHC antigens.

no MHC antigens > no foreign cells > no immune reaction
 

Offline alastair84

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Re: placenta
« Reply #4 on: 14/05/2004 12:34:49 »
Perfect, thanks. you learn something new everyday.
 

Offline chris

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Re: placenta
« Reply #5 on: 14/05/2004 14:54:02 »
The placenta is of embryonic / foetal origin.

Following fertilisation the egg initiates a phase of rapid cell division (by mitosis). Fairly soon 2 cell populations become visible - a cluster or ball of cells inside the embryo - the embryonic knot - suspended in a cavity (the blastocyst) and surrounded by another layer of cells - the trophoblast.

When the embryo settles on the lining of the uterus the trophoblast begins to invade the upper layers of the endometrium (the decidual tissue that lines the uterus and is shed during a period).

The trophoblast extends finger-like projections into the endometrium. This is the future placenta. Beneath the outer layer (called the syncitiotrophoblast) lies a single-celled layer (the cytotrophoblast) below which a cell population called mesoderm proliferates and produces all of the blood vessels of the future placenta and umbilical cord.

The trophoblast grows invasively into the wall of the uterus rather like a cancer. When it reaches the correct depth this pattern of growth is arrested. Occasionally this process goes wrong and the trophoblast continues to grow, quite literally as a cancer. This is referred to as a molar pregnancy (hydatidiform mole).

Chris

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Offline Donnah

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Re: placenta
« Reply #6 on: 15/05/2004 22:05:25 »
I thought a molar pregnacy was when the embryo was growing outside the uterus.
 

Offline chris

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Re: placenta
« Reply #7 on: 16/05/2004 06:03:07 »
A conceptus growing anywhere other than in the uterus is referred to as an ectopic pregnancy. These can occur anywhere from the ovary and pelvis to the vagina. However, the commonest site is in the oviduct (fallopian tube) because this is the narrowest point through which the embryo must pass, and this site is readily scarred (and further narrowed) by infection, particularly chlamydia.

Chris

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Offline Rokitansky

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Re: placenta
« Reply #8 on: 16/05/2004 15:22:11 »
I think that the hydatidiform mole is one of the most potent tumors.
 

Offline Rokitansky

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Re: placenta
« Reply #9 on: 17/05/2004 19:45:07 »
quote:
Originally posted by calcaneus

.

Embryo with its covering stuctures is geneticly unique foreign body. Immune reaction is not caused because of changed expression of MHC antigens from trophoblast cells.
MHC antigens are superficial molecules. Identified by T-lymfocites, forein cells with MHC antigens are being destroyed.
That is why trophoblast cells DO NOT produce MHC antigens.

no MHC antigens > no foreign cells > no immune reaction



Beside of the MHC suppression, other mechanisms like anergy and the lack of inflamatory reaction (there is no tissue damage, and therefore no inflamatory mediators are released)  which is necessary  “second signal” for immune system to react, are included.
 

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Re: placenta
« Reply #9 on: 17/05/2004 19:45:07 »

 

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