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

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

Decidua basalisDecidua capsularis

Decidua parietalis

Uterine cavity

Dr.Sherif Fahmy

Dr. Sherif Fahmy

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

Dr. Sherif Fahmy

Decidua basalis

Decidua parietalis

Decidua capsularis

Uterine cavity

Fused decidua parietalis and capsularis

Decidua basalis

Dr. Sherif Fahmy

3rd Week of PregnancyA- Changes in the chorion.B- Changes in the embryonic disc.

Maturation of blastocyst

Dr. Sherif Fahmy

Maturation of blastocystChorionic vesicle Blastocyst

Dr. Sherif Fahmy

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

Chorionic Vesicle (at the end of 3rd week)

Changes in the chorionFormation of chorionic velli:1- Primary velli.2- Secondary velli.3- Tertiary velli

A-Chorion frondosum.B-Chorion leave.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Syncytiotrophoblast

Cytotrophoblast

Primary chorionic velli

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Secondary chorionic velli

Syncytiotrophoblas

Cytotrophoblast

Somatic mesoderm

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Fetal blood vessels

Tertiary velli (chorion frondosum)

Tertiary velli (chorion leave)

Cytotrophoblastic shell

Tertiary chorionic velli

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Chorion frondosum

Dr. Sherif Fahmy