Download Foetal Membranes

Foetal Membranes
• Second month : the tropho blast develops
secondary and tertiary villi
• Villi are anchored to the mesoderm of the
chorionic plate and peripherally attached
to the maternal decidua by cytotrophoblast
Amnion
Definition : • The thin, transparent inner membrane (the chorion is the
outer layer) that constitutes the amniotic membranes.
• contain the amniotic fluid
• A protective layer for the baby insulating him/her from
bacteria in the vagina. Rupture of this sac exposes the
child to bacteria in the vagina and increases the risk of
infection if the infant is not delivered within about 18
hours.
• Labor usually starts shortly after of before rupture of the
amniotic membranes.
• Amniotic fluid - watery liquid surrounding and cushioning a growing
fetus within the amnion. It allows the fetus to move freely without the
walls of the uterus being too tight against its body.
• The amnion grows and begins to fill, mainly with water, around two
weeks after fertilisation. After a further 10 weeks the liquid contains
proteins, carbohydrates, lipids and phospholipids, urea and
electrolytes.
• The fluid is released when the amnion ruptures - spontaneous
rupture of membranes (SRM).
• The majority of the amniotic fluid remains inside the uterus until the
baby is born.
Complications related to amniotic fluid
• Too little amniotic fluid (oligohydramnios)
• Too much (polyhydramnios or hydramnios)
• In both cases the majority of pregnancies proceed normally and the
baby is born healthily.
• Polyhydramnios is a predisposing risk factor for cord prolapse.
•
A rare and fatal obstetric complication is an amniotic fluid embolism.
Multiple pregnancies
•
Twins and multiple pregnancies sometimes share the amnion and the chorion.
•
Monoamniotic pregnancy is when each embryo or fetus from one single zygote
(monozygotic, commonly known as identical twins) is located within the same amnion
which is itself in one chorion (monochorionic).
•
Diamniotic pregnancy is when there are more than one amnions inside one chorion
or each having their own chorion (dichorionic).
•
Dizygotic (fraternal, non-identical) twins each have their own amnion and chorion and
may or may not share a placenta.
Chorion
Definition
• Is a membrane closely adherent to the amniotic
membrane.
• It is formed during the second week of development
• The chorionic cavity is one of the first two cavities
formed during the second week of development.
• It is otherwise called extraembryonic coelom
• Later on the amniotic cavity enlarges and after the
folding of the embryo it occupies and fills the whole of
the chorionic cavity and then obliterates the chorionic
cavity. Then the chorion and amnion fuse together. They
enlarge and fill the whole of the uterus.
• The extraembryonic mesoderm lining the inside of the cytotrophoblast is
then known as the chorionic plate. The lining of the chorionic cavity
connects with the germ disc by a stalk called the connecting stalk