Fetal Membranes, Placenta andBirth defects
Jun Zhou(周俊)School of Medicine, ZheJiang University
20160113
Fetal membrane — overview •Originate from blastocyst, don’t participate in the formation of embryo•Including:1) Chorion2) Amnion3) Yolk sac4) Allantois5) Umbilical cord
Chorion•Formed bytrophoblast +extraembryonic mesoderm•Chorion frondosum (bushy chorion)- embryonic pole•Chorion laeve (smooth chorion)- abembryonic pole
Development of villiWeek 2 to week 3 Primary villi: cytotrophoblast+syncytiotrophoblast Secondary villi: extraembryonic mesoderm enter the primary villi Tertiary villi: extraembryonic mesoderm =>CT+BV
Function of Chorion1) Exchange of metabolite: 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 secretionsOutput: 1) absorbed by amniotic cells 2) fetus swallow
•30 ml--- 10 weeks•450 ml--- 20 weeks•800-1000 ml --- 37 weeks---circulate
Amnion - Fluid Functions
Mechanically cushion Protect from fetus adhesion Movement Maintain Temp
Abnormalities1) too much (polyhydramnios) >2000 ml Abnormal digestive system or CNS - esophageal atresia - anencephaly2) too little (oligohydramnios) <500 ml Abnormal urinary system - poor development of kidney - urethra atresia
Yolk sac and Allantois Yolk sac
Primitive Gut 3rd week, Germ Cells 3rd to 6th week, Blood island
Allantois Caudal extension of
hindgut Allantoic A pairs Allantoic V pairs
Umbilical vessels 2A+1V
Umbilical Cord
Folding – a purse string closure Amnion membrane covered Cord: mucous CT, 3
vessels,yolk sac ,allantois At birth, 50-60 cm, 2cm
diameter Long – knots Short – placenta detachment
Placenta - Overview Functions as:
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 spaceumbilical V
Mother: spiral A intervillous space uterine V
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 Function1.Exchange of Metabolites: nutrients
antibody, waste 2.Defense barrier3.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 proliferationCell migrationCell differentiation