The Placenta and the Embryo Per Brodal Institutt for medisinske basalfag Universitetet i Oslo 9th Semester 2008

Week 12 England P. Brodal 2008 Approx. 6 cm Crown Rump (CR) length

Week 12 (approx.) Placenta Fetal membranes England P. Brodal 2008

Week 7 England 1983 Placental villi Amnion 4 P. Brodal 2008

Placenta Larsen, 3d Edition Placental villi 5 P. Brodal 2008

The First Week Day 5: Blastocyst Day 6: Implantation Day 4: Morula Shedding of the zona pellucida Fertilization 6 P. Brodal 2008

Implantation – 6th day Endometrium Inner cell mass: gives rise to the embryo Outer cell mass (trophoblast): gives rise to the placenta Trophoblast start to invade the endometrium 7 P. Brodal 2008 Langman, 8 Ed.

Chorion and Decidua (End of Second Month) Decidua basalis Chorion frondosum (villi) Chorion laeve Decidua capsularis Decidua parietalis Amniotic cavity Chorion: forms fetal part of the placenta Decidua: forms maternal part of the placenta Chorion: forms fetal part of the placenta Decidua: forms maternal part of the placenta Langman, 8 Ed. 8 P. Brodal 2008

Decidua – Transformed Cells of the Endometrial Stroma Decidua capsularisDecidua parietalis  large, round, epithelial-like cells  secrete nutrients and regulatory substances  Important for successful placentation 9 P. Brodal 2008

7th day Endometrium changes: Decidual reaction Syncytiotrophoblast Cytotrophoblast Amnioblasts Ectodermal cells Entodermal cells 10 P. Brodal 2008 Langman, 8 Ed.

9th day: Further Development of the Placenta Cytotrophoblast Lacunae in the syncytiotrophopblast Maternal blood vessels 11 P. Brodal 2008

12 days Primitive yolk sac Maternal sinusoids connect with lacunae in the trophoblast Endometrial epithelium 12 P. Brodal 2008 Langman, 8 Ed.

13 days Trophoblastic lacunae present all around the embryo Extra-embryonal coelom (chorionic cavity) Amniotic cavity Yolk sac Sometimes a small bleeding occurs at this stage 13 P. Brodal 2008 Langman, 8 Ed.

End of Third Week Cytotrophoblast Syncytiotrophoblast The cytotrophoblast grows through the syncytiotrophoblast to form an external shell 14 P. Brodal 2008 Langman, 8 Ed.

The Cytotrophoblastic Shell (End of 3d Week) Umbilical cord Cytotrophoblasts Syncytiotrophoblast 15 P. Brodal 2008 Langman, 8 Ed.

Placental Villi – at Fourth Week and Fourth Month Cytotrophoblast shell Syncytiotrophoblast Villus with extra-embryonal mesoderm Maternal blood vessels Decidua (endometrium) Villous blood vessels (fetal) Intervillous space (maternal blood) 16 P. Brodal 2008

Development of the Villi Primary villusSecondary villusTertiary villus (end of third week) Diffusion barriere Early Late 17 P. Brodal 2008 Langman, 8 Ed.

Foeto-Placental Circulation (End of 4th Week) Umbilical artery (2) Umbilical vein (1) Dorsal aorta Cardinal veins (anterior and posterior) Yolk sac Vitelline artery Placental villi 18 P. Brodal 2008

The Placenta at Term Chorionic plate Decidual plateSpiral artery Umbilical cord Amnion Decidual septum 19 P. Brodal 2008

The Placenta at Term cm diameter, g, 3 cm thick Exchange area: ~ 10 m 2 Blood flow: 600 ml/min cm diameter, g, 3 cm thick Exchange area: ~ 10 m 2 Blood flow: 600 ml/min AmnionUmbilical cord Cotyledon Decidual layer removed 20 P. Brodal 2008

Extravillous Trophoblast  Trophoblastic cells growing as columns into the decidua, forming anchoring villi  Invading also the uterine arteries – eroding the media and forming the intima  Important for maintaining perfusion of the placenta  Inadequate formation: related to preeclampsia  Ecxessive: invasive growth, e.g. choriocarcinoma 21 P. Brodal 2008 Langman, 8 Ed.

The Fetal Membranes (End of 4th Month) Fusion of amnion, chorion laeve, decidua capsularis and decidua parietalis Fusion of amnion, chorion laeve and decidua capsularis 22 P. Brodal 2008

Fetal Membranes Amnion (vannhinnen) 23 P. Brodal 2008

Fetal membranes – Dizygotic twins 2 cell - zygote Fused chorions Langman 24 P. Brodal 2008

Fetal membranes - Monozygotic Twins 2-cell zygote Split at 2-cell stage; separate chorion and amnion Split of inner cell mass early; share chorion, separate amnion Split of inner cell mass late; share chorion and amnion Langman 25 P. Brodal 2008

Formation of The Umbilical Cord Amnion Yolk sac 26 P. Brodal 2008

Bilaminar germ disk (2d week) Amnion Entoderm Ectoderm 27 P. Brodal 2008 Langman, 8 Ed.

Formation of the Mesoderm (2d-3d Week) Week 3 Ectoderm Entoderm Mesoderm 28 P. Brodal 2008 Langman, 8 Ed.

Third week – Trilaminated Disc Langman Amnion Amniotic cavity Yolk sac Entoderm Ectoderm Mesoderm (paraxial) Intra-embryonic coelom (starting to form) 29 P. Brodal 2008

Foldings Determine the Shape of the Embryo (Fourth week) Langman Intraembryonic coelom Midgut Yolk sac Amniotic cavity Paraxial mesoderm (somit) Intermediate mesoderm (nephrotomes) Neural tube 30 P. Brodal 2008

Some Landmarks in Embryonic Development  2d-3d week: The trilaminar germ disc formed  3d week: The heart develops, links up with the vascular system  4th week: Formation of the gut  6th week: Urogenital sinus formed  7th week: most organs have formed 31 P. Brodal 2008

Some Landmarks in Fetal Development (weeks after fertilization)  6 weeks ~ 2 cm CR-length; nose, ears, fingers identifiable  10 weeks ~ 6 cm; external genitals formed but undifferentiated  14 weeks ~ 12 cm; external genitals can be differentiated, skin transparent red  18 weeks ~ 15 cm; fine hairs (lanugo) covers the body, skin opaque  22 weeks ~ 21 cm; eyebrows and fingernails present  26 weeks ~ 26 cm; eyes open, scalp hair growing Llewellyn-Jones 7th Ed. 32 P. Brodal 2008