Placenta formation

1. PLACENTA
The human placenta is a fetomaternal organ – discoid, haemochorial, deciduate, larynthine
structure attached to the uterine wall and establishes connection between the mother and fetus
through the umbilical cord.
Structure of placenta
It has two surfaces/components - Fetal surface: from chorion frondosum is smooth and shiny
because it is covered by an amniotic membrane. The umbilical cord is attached centrally to this
surface. At term about four –fifths of the placenta is of fetal origin. Maternal surface: from decidua
basalis is rough and spongy, reddish, and has 15 – 20 elevated/polygonal areas called cotyledons
with deep grooves/fissues in between made by the decidual septa. Maternal blood gives it a dull
red colour. Only the decidua basalis and the blood in the intervillous space are of maternal in
origin. By the end of the 4th month, the decidua basalis is almost entirely replaced by the fetal part
of the placenta. During the 4th and 5th month, the decidua forms a number of decidual septa, which
project into the intervillous space.
The placenta consists of two plates— 1. The chorionic plate lies internally and lined by amniotic
membrane. The umbilical cord is attached to this plate. 2. The basal plate lies to the maternal
aspect. Between the two plates lies the intervillous space containing the stem villi and their
branches the space being filled with maternal blood.