Placenta Physiology
The placenta develops from the single layer of trophoblasts in the inital blastocyst
All materials necessary for foetal growth and development move from maternal circulaton to foetal
circulaton across the placenta
Transport processes involved
o Passive difusion (O2 & CO2)
o Facilitated difusion
o Actve transport
Waste products largely excreted via amniotc fuid
Development
1) Blastocyst adheres to endometrial epithelium (i.e. at implantaton) Trophoblast cells diferentate into
- cytotrophoblasts (inner)
- sycncytiotrophoblasts (outer)
2) A multinucleated mass is formed as cytotrophoblasts proliferate and migrate into sycncytotrophoblast,
losing their cell membranes.
3) Blastocyst embeds into endometrium as cytotrophoblasts secrete proteolytc
enzymes and sycncytotrophoblasts send out fnger-like projectons
4) Lacunae (spaces) form between sycncytotrophoblasts as the
sycncytotrophoblasts erode endometrial blood vessels and glands these fill wilth
maternal blood and glandular secretons.
Layers (inside to out):
Extraembryonlc mesoderm Cytotrophoblasts sycncytiotrophoblasts Decldual basalls
- Note: Decidual cells are large round/ oval/ polygonal cells. Their cytoplasm are rich in
glycogen and lipids, actng as a rich source of nutriton for developing embryo.
5) Prlmary chorlonlc vllll (end of week 2) small projectons of cytotrophoblasts
expand into the sycncytotrophoblast
6) Secondary chorlonlc vllll (start of week 3) extraembryonic mesoderm grows into
these villi forming a core of loose CT
7) Tertiary chorlonlc vllll (end of week 3) embryonic blood vessels form in
extraembryonic mesoderm
- Anchoring villi - Some cytotrophoblasts grow outwards to the Decidual
basalis, and past it to form the cytotrophoblastic shell
- Branch villi - Some cytotrophoblasts grow into the lntervlllous space The
main site of exchange between mother and foetus
8) Foetal blood fowi (week 4) two umbilical arteries (carrying deoxygenated foetal blood to placenta) and
one umbilical vein (carrying oxygenated blood from placenta to foetus)
Exchange across Mature Placenta
1) Maternal arterial blood discharged from the 120 splral arterles in
pulsatle spurts through wall of uterus
2) Maternal blood moves into lntervlllous space (the fuid-flled,
merged lacunae) where exchange takes place across the
placental membrane
3) Blood fow slows to “bathe” chorionic villi allowing adequate
tme for exchange into the umbilical vein
4) The umblllcal veln (X1) carries oxygenated blood to the foetus
5) Foetal waste products are carried back to the intervillous space via
umblllcal arterles (x2) which carry deoxygenated blood. They
approach placenta and branch many tmes to form capillary
network.
The placenta develops from the single layer of trophoblasts in the inital blastocyst
All materials necessary for foetal growth and development move from maternal circulaton to foetal
circulaton across the placenta
Transport processes involved
o Passive difusion (O2 & CO2)
o Facilitated difusion
o Actve transport
Waste products largely excreted via amniotc fuid
Development
1) Blastocyst adheres to endometrial epithelium (i.e. at implantaton) Trophoblast cells diferentate into
- cytotrophoblasts (inner)
- sycncytiotrophoblasts (outer)
2) A multinucleated mass is formed as cytotrophoblasts proliferate and migrate into sycncytotrophoblast,
losing their cell membranes.
3) Blastocyst embeds into endometrium as cytotrophoblasts secrete proteolytc
enzymes and sycncytotrophoblasts send out fnger-like projectons
4) Lacunae (spaces) form between sycncytotrophoblasts as the
sycncytotrophoblasts erode endometrial blood vessels and glands these fill wilth
maternal blood and glandular secretons.
Layers (inside to out):
Extraembryonlc mesoderm Cytotrophoblasts sycncytiotrophoblasts Decldual basalls
- Note: Decidual cells are large round/ oval/ polygonal cells. Their cytoplasm are rich in
glycogen and lipids, actng as a rich source of nutriton for developing embryo.
5) Prlmary chorlonlc vllll (end of week 2) small projectons of cytotrophoblasts
expand into the sycncytotrophoblast
6) Secondary chorlonlc vllll (start of week 3) extraembryonic mesoderm grows into
these villi forming a core of loose CT
7) Tertiary chorlonlc vllll (end of week 3) embryonic blood vessels form in
extraembryonic mesoderm
- Anchoring villi - Some cytotrophoblasts grow outwards to the Decidual
basalis, and past it to form the cytotrophoblastic shell
- Branch villi - Some cytotrophoblasts grow into the lntervlllous space The
main site of exchange between mother and foetus
8) Foetal blood fowi (week 4) two umbilical arteries (carrying deoxygenated foetal blood to placenta) and
one umbilical vein (carrying oxygenated blood from placenta to foetus)
Exchange across Mature Placenta
1) Maternal arterial blood discharged from the 120 splral arterles in
pulsatle spurts through wall of uterus
2) Maternal blood moves into lntervlllous space (the fuid-flled,
merged lacunae) where exchange takes place across the
placental membrane
3) Blood fow slows to “bathe” chorionic villi allowing adequate
tme for exchange into the umbilical vein
4) The umblllcal veln (X1) carries oxygenated blood to the foetus
5) Foetal waste products are carried back to the intervillous space via
umblllcal arterles (x2) which carry deoxygenated blood. They
approach placenta and branch many tmes to form capillary
network.
