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Placenta

From Mediwikis

Overview

Has both embryonic part and maternal part, it is an exchange surface formed from the uterus and the embryo. Embryonic part is corion or chorionic plate, maternal is deciduous. Embryonic part is formed from the extra embryonic mesoderm and the trophoblast, the outer layer of the blastocyst.

Inner cell mass develops epiblast and hypoblast. Trophoblast become cytotrophoblast and the syncytiotrophoblast. Hypoblast and epiblast form from inner cell mass. Lacunae are spaces in the syncytiotrophoblast where maternal blood will come through. They form on day nine.

The syncytiotrophoblast itself is formed by the mitotic division and then fusion of cytotrophoblast cells.

In the early stages of implantation the amniotic cavity is surrounded by the amnion which is surrounded by the epiblast on one side and the cytotrophoblast on all others. The cavity which is formed by the cytotrophoblast and contains the amnion and the epiblast is the blastocyst cavity. The Embryonic pole is where the embryo is, abembryonic pole is opposite. During days 11-12 the blastocyst completely embeds within the endometrial stroma.

Extra embryonic mesoderm forms from the hypoblast. It forms another cavity around the blastocyst called the chorionic cavity. This decreases in size as pregnancy goes on to be obliterated as amniotic cavity grows. Also uterine cavity or lumen is taken up by amniotic cavity.

Cells of the uterus undergo decidual reaction which spreads throughout the whole endometrium and is essentially the cells becoming charged with lipids and glycogen. From the outside in the levels of the uterus are the perimetrium then myometrium then endometrium.

The chorion is a multilayered structure consisting of the somatic layer of the extra embryonic mesoderm, cytotrophoblast and syncytiotrophoblast.

Amniotic cavity has fetus in it and expands to fill chorionic cavity. Membrane is derived from the epiblast. The fluid cushions the fetus and forms a hydrostatic wedge which assists with uterus dilation during labour.

Extra embryonic mesoderm forms chorionic plate and villi which connect to outer cytotrophoblast shell. This she'll is penetrated by blood vessels near where the fetus is anchored to start placental formation. Decidua capsularis is the bit which envelops the trophoblast. Blood vessels from it penetrate into the intervillus space.

Early on there is a thick diffusion barrier but in thins over time to allow more gas exchange.

Chorion fondosom is bushy as it has plunged into the endometrium with lots of villi at the embryonic end while the smooth chorion or leaf chorion are less developed and is present at the abembryonic pole.

Decidua is the functional layer of the endometrium. Shed during parturition. As it develops it forms cotyledon while the place on the placenta on which the baby is anchored is the embryonic plate.

Amniotic fluid

If in the blood it can cause embolism. Generally swallowed by baby and also urinated out by baby after the fifth month. If for some reason the baby cannot do this polyhydramnios can occur.

Function of placenta

Gases, facilitated diffusion, active transport, pinocytosis (IgG antibodies) and sometimes fetal red blood cells.

Placental abnormalities

Foetal hydrops If you have a rhesus negative baby carried by a positive mother foetal red cells will go to the mother and make antibodies be produced. In the second pregnancy the antibodies will cross over and cause destruction of foetal red cells. This causes heart failure so the baby swells and dies.

By the end of the fourth month the placenta takes over hormone control.

Ectopic pregnancy When egg implants in other area than uterine wall. Usually Fallopian tube. Most commoner risk factor is narrowed and scarred Fallopian tube usually due to STDs.

Placenta praevia Low uterine placenta. Causes painless 3rd trimester bleeding as it is ripped and needs c section. Essentially it covers uterine os.

Placental abruption Separation of placenta and Decidua (functional part of uterus) prior to delivery. Third trimester bleeding and fetal insufficiency.

Placenta accreta Improper implantation of the placenta into the myometrium so won't separate properly. Difficult placental delivery.

Pre eclampsia Pregnancy specific multi system disorder with a genetic predisposition. The second wave of a trophoblast invasion doesn't happen properly, lack for formation of spiral arteries correctly, they are too thin. Causes hypertension, proteinuria and odema in third trimester usually. Due to an abnormality in the maternal vascular interface in the placenta. Pre eclampsia is technically this plus seizures. Risk factors include first time mums and pre existing hypertension. Try to keep bp at stable state until you deliver the baby. Do not use ACE inhibitors as they damage the baby. Acute severe hypertension from pre eclampsia can cause fits. Use IV drugs to bring down blood pressure or chemicals which reduce chance of seizure. Avoid the. Having a fit at all costs, all seizures treated as eclampsia until proven otherwise. Treatment is magnesium sulphate. Steroids help fetal lungs develop

Hydatinaform mole Placenta growing out of control. No baby though. Picked up on ultrasound as no baby heartbeat. Snowstorm appearance on ultrasound. Can lead to Chorionic carcinoma.