Fertilization & Fetal Development
Fertilization & Fetal Development
Fertilization & Fetal Development
IMPLANTATION
CHORIONIC VILLI
► Are villi that sprout from the
chorion to provide maximal
contact area with maternal
blood. Villi are part of the
border between maternal &
fetal blood during
pregnancy.
► Chorionic villi have a central
core of loose connective
tissue surrounded by a double
layer of trophoblast cells. The
central core of connective
tissue contains fetal
capillaries.
► The outer of the two covering
layers is termed the
syncytiotrophoblast, or the
syncytial layer. This layer of
cells is instrumental in the
production of various
placental hormones, such as
HCG, somatomammotropin
(human placental lactogen),
estrogen & progesterone.
► The inner layer, known as the
cytotrophoblast or Langhans’
layer, is present as early as 12
days’ gestation & appears to
be functional early in ⮚ the endometrium is now
pregnancy but then termed decidua (the Latin
disappears between the 20th word for “falling off”), because
& 24th week. This layer of cells it will be discarded following
protect the growing embryo the birth of the child. The
& fetus from certain decidua has three separate
infectious organisms such as areas:
the spirochete of syphilis. • Decidua basalis – or the
This is why syphilis is part of the endometrium
considered to have high lying directly under the
potential for fetal damage late embryo (or the portion
in pregnancy, when where the throphoblast cells
cytotrophoblast cells are not are establishing
functioning. Unfortunately, the communication with
layers appear to offer little maternal blood vessels)
protection against viral • Decidua capsularis – or the
portion of the endometrium
that stretches or
encapsulates the surface of
the trophoblast
• Decidua vera – or the
remaining portion of the
uterine lining
Layers of Decidua Basalis and
Decidua Vera
• Zona Compacta –
uppermost/surface layer made
up of compact cells
invasion. • Zona Spongiosum – middle,
spongy layer; with glands and
small blood vessels
THE DECIDUA
• Zona Basalis – lowest
most/basal layer
✔ The zona basalis & zona
spongiosum together form
the functional layer (zona
functionales). Implantation is
up to the level of spongiosum
✔ The zona basalis remains after fibrous tissue with sparse
delivery/placental separation vessels confined mainly to the
Decidual Aging: Nitabuch’s layer, base
a zone of fibrinoid degeneration, is • Average weight at term: 500
where invading trophoblast meets gm
the decidua. This layer is usually • Feto-placental weight ratio at
absent whenever the decidua is term – 6:1
defective.