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

OBJECTIVES

1. The components of fetal membrane and their functions.

2. Structure and function of placenta.3. The periods of vulnerability.4. Composition of Placenta barrier.