The decidua is the endometrium that remains in the uterus after implantation. It is composed of three parts: the decidua basalis between the blastocyst and myometrium that forms part of the placenta, the decidua capsularis covering the blastocyst except at the embryonic pole and separating it from the uterine cavity, and the decidua parietalis lining the rest of the uterine cavity. After delivery, the decidua basalis shares in placenta formation while the decidua capsularis and parietalis fuse and are shed with the placenta.

1. Decidua
• It is endometrium after implantation
which is sheded after birth of fetus.
• Character of endometrium:
• Increased secretory function of uterine
glands.
• Decidual cells are endometrial cells filled with
glycogen.
• Arteries become more spiral with arterio-
venous anastomosis.
Dr. Sherif Fahmy

2. Parts of decidua:
• Decidua basalis: It is the part of decidua
between blastocyst and myometrium. It
forms the fetal part of placenta.
• Decidua capsularis: It covers the blastocyst
except embryonic pole and separates it from
uterine cavity.
• Decidua parietalis: It is the rest of
endometrium that lines the rest of uterine
cavity.
Dr. Sherif Fahmy

3. Decidua basalis
Decidua capsularis
Decidua parietalis
Uterine cavity
Dr.Sherif Fahmy
Dr. Sherif Fahmy

4. Fate of decidua:
• Decidua basalis shares in the
formation of placenta.
• Decidua capsularis and parietalis
fuse together and shedded with
placenta after delivery.
Dr. Sherif Fahmy

5. Dr. Sherif Fahmy
Decidua basalis
Decidua
parietalis
Decidua
capsularis
Uterine
cavity
Fused decidua
parietalis and
capsularis
Decidua
basalis
Dr. Sherif Fahmy

6. 3rd
Week of Pregnancy
A- Changes in the chorion.
B- Changes in the embryonic
disc.

7. Maturation of blastocyst
Dr. Sherif Fahmy

8. Maturation of blastocyst
Chorionic vesicle Blastocyst
Dr. Sherif Fahmy

9. 13th
day
Endodermal
cells
Secondary yolk
sac
Exocoelomic cyst
Somatic
mesoderm
Connecting stalk
Somatic
mesoderem
Splanchnic
mesoderm
1ry chorionic villi
Extra-
embryonic
coelom
Chorionic
cavity)
Dr.Sherif Fahmy
Cyto-
trophoblast
Amniotic
cavity
Chorionic
Vesicle
Dr. Sherif Fahmy

10. Chorionic Vesicle (at the end of 3rd
week)

11. Changes in the chorion
Formation of chorionic velli:
1- Primary velli.
2- Secondary velli.
3- Tertiary velli
A-Chorion frondosum.
B-Chorion leave. Dr. Sherif Fahmy

12. Dr. Sherif Fahmy
Syncytiotrophoblast
Cytotrophoblast
Primary chorionic velli
Dr. Sherif Fahmy

13. Dr. Sherif Fahmy
Secondary chorionic velli
Syncytiotrophoblas
Cytotrophoblast
Somatic mesoderm
Dr. Sherif Fahmy

14. Dr. Sherif Fahmy
Fetal blood
vessels
Tertiary velli
(chorion frondosum)
Tertiary velli (chorion leave)
Cytotrophoblas
tic shell
Tertiary chorionic velli
Dr. Sherif Fahmy

15. Dr. Sherif Fahmy
Chorion
frondosum
Dr. Sherif Fahmy