Placenta formation is an important topic in anatomy, as it is a complex process that involves the development and function of the placenta during pregnancy. The placenta is a vital organ that connects the developing fetus to the mother's uterine wall, allowing for the exchange of nutrients, oxygen, and waste products. The placenta also plays a crucial role in hormone production, immune protection, and fetal development.
In the NEET PG Exam, questions related to placenta formation may be asked to test the student's understanding of the anatomy and physiology of the placenta, as well as its role in fetal development and pregnancy. A thorough understanding of placenta formation is essential for medical students.
Read this blog further to get a quick overview of this important anatomy topic for NEET PG/NExT exam preparation.
EXTRA EMBRYONIC MESODERM splits to form EXTRA EMBRYONIC coelomic CAVITY which is connected by CONNECTING STALK
Covers amniotic cavity
Somatopleuric layer of EEM
somatopleuric layer of EEM
Trophoblast divides to form
form placental membrane
Extra Embryonic Coelomic Cavity
It divides the extra embryonic mesoderm into two parts.
One towards the yolk sac is called as visceral or splanchnopleuric extra – embryonic mesoderm and beyond that lines the amniotic cavity and outside is called the parietal or somatopleuric extraembryonic mesoderm (towards body wall)
Between somatopleuric extraembryonic and visceral/ splanchnic mesoderm is the extra embryonic coelomic cavity.
Chorion formed by trophoblast with a somatopleuric layer of extraembryonic mesoderm.
Amnion formed by amniogenic cells lining the amniotic cavity and somatopleuric layer of extraembryonic mesoderm.
Connecting stalks later become umbilical cord components.
1° YOLK SAC → lined by ﬂattened Endodermal cells
2° YOLK SAC → lined by cuboidal Endodermal cells
3°YOLK SAC → formed during cephalo caudal development of Embryo →forms gut tube → Part of the yolk sac remaining outside the Embryo - 3 YOLK SAC
In the beginning, we had a primary yolk sac. Later it will become secondary yolk sac and then tertiary yolk sac. Tertiary yolk sac communicates with midgut as vitello – intestinal duct.
Extra – Embryonic coelomic cavity forming around the baby, there is cephalo- caudal folding of baby. Head comes towards the tail and in this process an amniotic cavity surrounds the body of the baby all around.
Allantois and the Vitello intestinal duct [midgut diverticulum] will enter the umbilical cord to become its contents.
Placenta formed by fetal & maternal contributions
Placenta formation: Decidua basalis from the maternal side and from the fetal side is chorion frondosum. Chorion layer develops some villi called chorionic villi and they will penetrate into decidua basalis of the maternal side.
Maternal placenta is decidua basalis [endometrium of uterus] and chorionic villi from fetal placenta component.
DECIDUA BASALIS [DB] → The endometrium where the embryo implants →forms the maternal /uterine placenta
DECIDUA CAPSULARIS → Surrounds the embryo on luminal side DONOT FORM PLACENTA
DECIDUA PARIETALIS →The rest of the gravid endometrium
Derived from chorion
CHORION FRONDOSUM - chorion towards DB forms layer like projections into it
CHORION LAEVE - chorion on the side of D. capsularis, DO NOT FORM PLACENTA
Uterine cavity = Space b/w decidua basalis & Parietalis
Chorionic cavity = Chorion & Amnion
PRIMARY VILLUS [Day 12]
Core of cytotrophoblast cells, covered by syncytio TB
SECONDARY VILLUS [Day 13-15]
Cytotrophoblast layer invaded by extra Embryonic mesoderm
TERTIARY VILLUS [Day 17-21]
Fetal blood vessels invades the mesoderm
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