Dr. Ikhlas Osman Embryonic Membranes

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Fetal membranes all the structure developed from the zygote and do not share in the formation of the embryo they include: Chorion. Allantois. Yolk sac. Umbilical cord. Amnoin. The fetal part of placenta.

Amnion The amnion is a membrane building the amniotic sac that surrounds the embryo. Develops on the dorsal aspect of the embryonic disc. The floor is the ectoderm The roof is the amniogenic epithelium.

Amnion Inner cell mass divides into Epiblast hypoblast. fluid filled sacs: Amniotic sac from epiblast Yolk sac from hypoblast.

Amnionic membrane epiblast derived extraembryonic ectodermal layer. The amnionic membrane is two cell layers epiblast derived extraembryonic ectodermal layer. thin non-vascular extraembryonic mesoderm. As the amnion enlarges it encompasses the embryo on the ventral side, emerging around the umbilical cord.

coelom

Chor i onic villi chorion As the amnion develops, it surrounds the embryo, and the umbilical cord begins to form from structures in the connecting stalk

Yolk sac Primitive yolk sac Primary yolk sac: the blastocoele lined by the exocoelomic membrane. Secondary yolk sac: a smaller cavity inside the primary yolk sac lined by the hypoblast. Definitive yolk sac the remaining part of the secondary yolk sac after folding connected to the midgut.

Allantois Solid endodermal outgrowth from the yolk sac then canalized and invades the connecting stalk. After folding it becomes connected to the cloaca and extend to the umbilical cord.

Changes after birth umbilical arteries change to the medial umbilical ligaments. Left umbilical vein to ligamentum teres of the liver. Allantois to the urachus to the median umbilical ligament. The mesoderm changes into jelly like material Called wartons jelly

Chorion Syncytiotrophoblast . Cytotrophoblast. The trophoblast forms two layers: Syncytiotrophoblast . Cytotrophoblast. The cytotrophoblast proliferates forming a new layer beneath the extraembryonic primary mesoderm.

Clefts appear in the mesoderm and fuse forming a chorionic cavity or extraembryonic coelom . The cavity divide the mesoderm in to outer and inner layers except a region connecting stalk or body stalk. The chorion formed of the: Syncytiotrophoblast . Cytotrophoblast. The outer layer of extraembryonic primary mesoderm.

Primary chorionic villi

chorionic villi The chorion sends finger-like chorionic villi which invade the decidua forming lacunae: Primary villi a core of cytotrophoblast surrounded by syncytiotrophoblast. Secondary villi a core of cytotrophoblast surrounded by syncytiotrophoblast and core of mesoderm. Tertiary villi a core of cytotrophoblast surrounded by syncytiotrophoblast and core of mesoderm invaded by fetal blood capillaries.

chorionic villi: primary villi develop week 2, consist of trophoblastic shell cells both syncitiotrophoblasts and cytotrophoblasts form finger-like extensions into the maternal endometrium . secondary villi Develop week3,extraembryonic mesoderm grows into villi, initially covers entire surface of chorionic sac. tertiary villi develop week 4, mesenchyme within secondary villi differentiates into blood vessels and cells, forms arteriocapillary network, fuse with placental vessels developing in connecting stalk.

Secondary chorionic villi

chorionic villi The types of chorionic villi: Anchoring villi The tertiary stem villi fix the embryonic vesicle to the decidua. The absorbing villi: The tertiary free villi increase the surface area. The fate of the chorionic villi: Villi opposite the decidua basalis enlarge form the chorion frondosum. The foetal part of the placenta. Villi opposite the decidua capsularis atrophy form the chorion laeve.

cytotrophoblastic shell The cytotrophoblast at the end of the anchoring villus penetrate the syncytiotrophoblast and extends in a lateral direction to fuse with other villi forming a continuous shell surrounding the embryonic vesicle to prevent further penetration of decidua by syncytiotrophoblast.

The umbilical cord The umbilical cord develops from the yolk sac and allantois. It forms by the fifth week of fetal development The cord joins the placenta. The umbilical cord in a full term neonate is usually about 50 cm long and about 2 cm diameter. The umbilical cord is composed of Wharton's jelly It contains one vein the umbilical vein. two arteries the umbilical arteries.

1. very long. > 120 cm coils around neck of the fetus. asphyxia 2. Very short. < 20 cm early separation of the placental. Knots a. False knots. b. true knot Battldore placenta Abnormal attachment to placenta 5. Velamentous insertion of the cord to the membrane not to placenta. anomalies