Pre-Natal DevelopmentPre-Natal DevelopmentChapter 17Chapter 17

CleavageCleavage 36hrs after fertilisation, 36hrs after fertilisation,

fertilised egg divides = fertilised egg divides = embryoembryo

Process continues from Process continues from oviducts to uterusoviducts to uterus

Hollow, fluid-filled ball Hollow, fluid-filled ball of cells formedof cells formed

Inner cells (next to Inner cells (next to fluid) – fluid) – embryonic areaembryonic area

Outer layer of cells Outer layer of cells (membrane) - (membrane) - chorionchorion

ImplantationImplantation Approx 1 week after fertilisationApprox 1 week after fertilisation Chorionic cells secrete enzymes Chorionic cells secrete enzymes

– digest endometrium wall– digest endometrium wall Embryonic area grows into Embryonic area grows into

endometrium wallendometrium wall Growth produces finger-like Growth produces finger-like

projections into maternal tissues projections into maternal tissues - become part of placenta- become part of placenta Eventually embryo drawn into & Eventually embryo drawn into &

surrounded by endometrium surrounded by endometrium – – implantationimplantation Embryo initially receives food & Embryo initially receives food &

oxygen from endometrial cells oxygen from endometrial cells

chorionic

DifferentiationDifferentiation Embryonic cells divide Embryonic cells divide

continuously by mitosiscontinuously by mitosis Mass of unspecialised Mass of unspecialised

cells formedcells formed Cells eventually become Cells eventually become

specialised = specialised = differentiationdifferentiation

All cells contain the same All cells contain the same genesgenes

Differentiation ‘switches Differentiation ‘switches on/off’ certain genes in on/off’ certain genes in certain cells certain cells

TwinsTwins Monozygotic (‘Identical’):Monozygotic (‘Identical’): Derived from a single egg Derived from a single egg

& sperm& sperm Developing embryo forms Developing embryo forms

2 separate embryonic 2 separate embryonic areas inside one ballareas inside one ball

Separate amnions (water Separate amnions (water sacs)sacs)

Same chorion & placentaSame chorion & placenta

TwinsTwins Dizygotic (‘Non-Identical’):Dizygotic (‘Non-Identical’): 2 eggs fertilised by 2 2 eggs fertilised by 2

spermsperm Embryo’s develop Embryo’s develop

independentlyindependently Amnion, chorion, and Amnion, chorion, and

placenta all their ownplacenta all their own Genetically dissimilar to Genetically dissimilar to

each othereach other

Exchanges between maternal & fetal Exchanges between maternal & fetal circulation - usefulcirculation - useful

Placenta is formed – villi Placenta is formed – villi project into the inner uterus project into the inner uterus wallwall

Villi have fetal & maternal Villi have fetal & maternal blood separated only by a very blood separated only by a very thin membranethin membrane

Useful:Useful: COCO22 & oxygen & oxygen diffusediffuse across across Glucose moves by Glucose moves by active active

transporttransport Antibodies move by Antibodies move by pinocytosispinocytosis

Exchanges between maternal & Exchanges between maternal & fetal circulation – harmful (1)fetal circulation – harmful (1)

ThalidomideThalidomide : : treated morning treated morning sickness (1950s)sickness (1950s)

Caused malformations, mental Caused malformations, mental disabilities in newbornsdisabilities in newborns

AlcoholAlcohol: : increases miscarriage increases miscarriage ratesrates

Damaged placental blood vessels Damaged placental blood vessels (oxygen supply inadequate)(oxygen supply inadequate)

Nutrient absorption impaired (Vit Nutrient absorption impaired (Vit BB66 & Zinc) & Zinc)

Fetal Alcohol SyndromeFetal Alcohol Syndrome – – growth abnormalities, heart growth abnormalities, heart defects, mental retardation defects, mental retardation

Exchanges between maternal & Exchanges between maternal & fetal circulation – harmful (2)fetal circulation – harmful (2)

Smoking:Smoking: CO – reduces oxygen CO – reduces oxygen

carried in the bloodcarried in the blood Nicotine – prevents Nicotine – prevents

adequate glucose adequate glucose supplysupply

Newborns often small Newborns often small & intellectually poorer& intellectually poorer

Exchanges between maternal & Exchanges between maternal & fetal circulation – harmful (3)fetal circulation – harmful (3)

Heroin:Heroin: Induces temporary relaxed Induces temporary relaxed

detachment from pain & detachment from pain & anxiety – content & sleepyanxiety – content & sleepy

Leads to dependency & Leads to dependency & painful withdrawalpainful withdrawal

Fetus can also get addictedFetus can also get addicted Vital processes slow downVital processes slow down Mother’s poor health affect Mother’s poor health affect

baby’s healthbaby’s health Baby often weak & undersizedBaby often weak & undersized Withdrawal symptoms – Withdrawal symptoms –

tremors, perspiration, tremors, perspiration, insomniainsomnia

Exchanges between maternal & Exchanges between maternal & fetal circulation – harmful (4)fetal circulation – harmful (4)

Rubella:Rubella: Similar to measlesSimilar to measles Congenital defects in Congenital defects in

newborns – eyes, ears & newborns – eyes, ears & heartheart

HIV:HIV: Virus can cross placenta Virus can cross placenta

(30% chance)(30% chance) Many babies develop AIDS Many babies develop AIDS

and die earlyand die early High termination rateHigh termination rate

Placental HormonesPlacental Hormones During gestation chorionic cell hormones stimulate During gestation chorionic cell hormones stimulate

corpus luteumcorpus luteum Oestrogen & Progesterone secreted = endometrial Oestrogen & Progesterone secreted = endometrial

developmentdevelopment 2 months – placenta takes over (Corpus 2 months – placenta takes over (Corpus

degenerates)degenerates) Oestrogen & Progesterone inhibit FSH & LHOestrogen & Progesterone inhibit FSH & LH Also stimulate milk-secreting tissue development in Also stimulate milk-secreting tissue development in

breastsbreasts LactationLactation (milk production) stimulated by (milk production) stimulated by prolactinprolactin

(only produced after birth)(only produced after birth)

Rhesus (Rh) FactorRhesus (Rh) Factor Rh-ve mother can have a Rh-ve mother can have a Rh+veRh+ve

babybaby Baby has Baby has D antigenD antigen – foreign to – foreign to

mothermother Initially mother’s immune system Initially mother’s immune system

unawareunaware At birth (or miscarriage) maternal At birth (or miscarriage) maternal

blood exposed to fetal bloodblood exposed to fetal blood Anti-D antibodiesAnti-D antibodies produced by produced by

mother’s immune systemmother’s immune system If pregnant again with Rh+ fetus – If pregnant again with Rh+ fetus –

fetal red cells attackedfetal red cells attacked Causes Causes HDNBHDNB (Hemolytic Disease of (Hemolytic Disease of

the Newborn)the Newborn) Treated by massive transfusionsTreated by massive transfusions Prevented by Prevented by anti-D immunglobulinanti-D immunglobulin

(destroys D antigens)(destroys D antigens)