Fetal Membranes, Placenta and Birth defects Jun Zhou（周俊） School of Medicine, ZheJiang University 20190114

Fetal membrane — overview Originate from blastocyst, don’t participate in the formation of embryo A collective group which include: 1) Chorion 2) Amnion 3) Yolk sac 4) Allantois 5) Umbilical cord

Chorion Formed by trophoblast +extraembryonic mesoderm Chorion frondosum (bushy chorion)- embryonic pole Chorion laeve (smooth chorion)- abembryonic pole

Development of villi Week 2 to week 3 Primary villi: cytotrophoblast+syncytiotrophoblast Secondary villi: extraembryonic mesoderm enter the primary villi Tertiary villi: extraembryonic mesoderm =>CT+BV

Function of Chorion Exchange of metabolite: 2) Hormone production: portion of placenta (Chorion frondosum) 2) Hormone production: human chorionic gonadotropin (HCG) ( Early indication of pregnancy)

Amnion Amniotic membrane: amniotic epi.+ extraembryonic mesoderm Amniotic fluid: Produce:1)amniotic cells 2) infusion of fluid from maternal blood 3) urine output from the fetus 4) pulmonary secretions Output: 1) absorbed by amniotic cells 2) fetus swallow Volume of amniotic fluid: 800-1000 ml --- 37 weeks Changes every 3 hours

Amnion - Fluid Functions Abnormalities Mechanically cushion Prevent from fetus adhesion Help fetal movement Maintain Temp. Abnormalities 1) too much (polyhydramnios) >1500 ml Abnormal digestive system or CNS - esophageal atresia - anencephaly 2) too little (oligohydramnios) <500 ml Abnormal urinary system - poor development of kidney - urethra atresia

Yolk sac and Allantois Yolk sac Allantois Primitive Gut 3rd week, Germ Cells, (migrate to mesoderm) 3rd to 6th week, Blood island ( the earliest hemapoietic organ) Allantois Caudal extension of hindgut Allantoic A pairs Allantoic V pairs Umbilical vessels 2A+1V

Umbilical Cord Embryonic folding produce a purse string closure Amnion membrane covered Cord: mucous CT, 3 vessels,yolk sac ,allantois At birth, 50-60 cm, 2cm diameter Too long – knots Too short – placenta detachment

Placenta - Overview Functions as: Placenta proper: Lungs, GI tract, Liver, Kidneys, Endocrine Placenta proper: Chorion frondosum (fetus)+ Decidua basalis (mother)

Anatomy of the Placenta Fetal – Chorion Chorion Frondosum Chorion Laeva Maternal – Decidua Decidua Basalis Decidua Capsularis Decidua Parietalis

Anatomy of the Placenta At birth 500 g 15-25 cm Diameter 3 cm thick Anchoring villi Decidual septa  15-20 Cotyledons

Placental-Fetal Circulation Fetus: umbilical A carries O2/nutrient depleted blood to cap. of chorion , exchange with maternal blood of the intervillous spaceumbilical V Mother: spiral A intervillous space uterine V

--the structure between fetal and maternal blood --components: Placental Barrier --the structure between fetal and maternal blood --components: 1)endothelium of chorion capillary 2) CT in the core of the villus 3) trophoblast epithelium

Placental Function 1.Exchange of Metabolites: nutrients antibody, waste 2.Defense barrier 3.hormone production human chorionic gonadotropin (HCG) Begin: end of 2nd week Highest: 2nd month Estrogen and progesterone Placental lactogen

Birth defect, congenital malformation and congenital anomaly Are synonymous terms used to describe structural, behavioral, functional and metabolic disorders present at birth

Causes of Birth Defects Genetic/Chromosomal - 15-20% Environmental (teratogens) - 10-15% Combined - 20-25% Multiple Gestations - 1% Unknown - 40-50%

Genetic Causes Molecules that regulate development Enzymes Structural genes Localized to a Chromosome – gene unknown

Environmental factors (Teratogens) Infectious agents-virus Physical agents X-rays, Hyperthemia, etc Chemicals agents alcohol, Cocaine, etc Hormones Maternal diabetes

Periods of Vulnerability Preembryonic period Pregerm (0-2 wks) Usually Death Embryonic period Organogenesis (3-8 wks) Abnormalities of Form (malformations) Fetal period Growth/Maturation (9 wks – birth) Growth Retardation Mental dysfunction Fetus vulnerable Rapid cell proliferation Cell migration Cell differentiation

OBJECTIVES The components of fetal membrane and their functions. Structure and function of placenta. The periods of vulnerability. Composition of Placenta barrier.