My study notes for all pathologists

1. FLASHPATH
H a z e m A l i

2. ANATOMY OF THE
PLACENTA
H a z e m A l i

3. GENERAL
• Placenta is a maternal-fetal organ that start developing following
implantation of blastocyst, and delivered with the fetus at birth
• Role of placenta:
– Protective function
• Encircle the fetus with amniotic sac (containing fluid)
• Attach the fetus to the uterine wall
– Vascular function
• Deliver nutrients, oxygen, and maternal antibodies to the fetus
• Remove waste products from the fetus
– Endocrine function
• Secret many hormones e.g. estrogen, progesterone, HCG

4. GENERAL
• The placenta formed of three parts:
–Placental disc
–Umbilical cord
–Fetal membranes
• The decidua share the maternal circulation with the placenta
Fetal
origin

5. PLACENTAL DISC
• Weight (at term):
– 400 – 600 gm
• Diameter (at term):
– 15 – 25 cm
• Thickness (at term):
– 1.5 – 3 cm
• Insertion (at the uterus)
– Commonly upper segment
– Commonly posterior wall
Before weighing the placenta, the disc should
be
“trimmed”  cord cut-off, membrane cut-off
“fresh”  not fixed by formalin (most weight
tables are based on fresh state)

6. PLACENTAL DISC
• Fetal surface
– Also called “chorionic plate”
– Covered by shiny, translucent membranes
• Fetal surface is light blue – pink
• Also showing radiating chorionic blood vessels
– Site of umbilical cord insertion
• Maternal surface:
– Also called “basal plate”
– Divided into 15 – 20, dark red lobules “cotyledons”
– Attached to the decidua basalis

7. UMBILICAL CORD
• Length (at term):
– 50 – 60 cm
• Diameter (at term):
– 1 – 3 cm
• Insertion (at the placenta)
– Chorionic plate (central / mildly eccentric)
• Cut section
– Two arteries (thick walled)
– One vein (thin walled)
– Wharton’s jelly (whitish – gelatinous)

8. UMBILICAL CORD
Twisting (coiling)
• Like the telephone cord
• Coiling index:
– Gross: total number of coils
total length of the cord
– Ultrasound: 1
intercoil distance (distance between two coils)
– Normal: 0.2 (+/- 0.1)
• One coil / 5 cm
• Up to three coils / 10 cm

9. FETAL MEMBRANES
• Forming the gestational sac
– Containing the fetus & amniotic fluid
• Features
– Smooth, glistening surface
• Layers
– Amnion (inner)
– Chorion (outer)
• Attachment (at the placenta)
– At the edges of the disc
The amnion reflects to cover the fetal
surface of the placental disc, and the outer
surface of umbilical cord

10. FETAL MEMBRANES
• Chorion Laeve (smooth)
– Free part
– Forming gestational sac (with amnion)
– No chorionic villi (atrophied)
• Chorion Frondosum (leaf-like)
– Embedded part in the placenta proper
– Forming chorionic plate
– Extending into chorionic villi

11. DECIDUA
• Endometrium of the pregnant uterus
– Contains maternal (endometrial) vessels
• Three parts
– Basalis: site of placental disc attachment
– Parietalis: lines of the rest of uterus
– Capsularis: covers the developing sac
• Eventually will fuse with the parietalis
in enlarged sac

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13. THANK YOU
H a z e m A l i