1. Pre-Natal Development Chapter 17

2. Cleavage • 36hrs after fertilisation, fertilised egg divides = embryo • Process continues from oviducts to uterus • Hollow, fluid-filled ball of cells formed • Inner cells (next to fluid) – embryonic area • Outer layer of cells (membrane) - chorion

3. Implantation chorionic • Approx 1 week after fertilisation • Chorionic cells secrete enzymes – digest endometrium wall • Embryonic area grows into endometrium wall • Growth produces finger-like projections into maternal tissues • - become part of placenta • Eventually embryo drawn into & surrounded by endometrium • – implantation • Embryo initially receives food & oxygen from endometrial cells

4. Differentiation • Embryonic cells divide continuously by mitosis • Mass of unspecialised cells formed • Cells eventually become specialised = differentiation • All cells contain the same genes • Differentiation ‘switches on/off’ certain genes in certain cells

5. Twins • Monozygotic (‘Identical’): • Derived from a single egg & sperm • Developing embryo forms 2 separate embryonic areas inside one ball • Separate amnions (water sacs) • Same chorion & placenta

6. Twins • Dizygotic (‘Non-Identical’): • 2 eggs fertilised by 2 sperm • Embryo’s develop independently • Amnion, chorion, and placenta all their own • Genetically dissimilar to each other

7. Exchanges between maternal & fetal circulation - useful • Placenta is formed – villi project into the inner uterus wall • Villi have fetal & maternal blood separated only by a very thin membrane • Useful: • CO2 & oxygen diffuse across • Glucose moves by active transport • Antibodies move by pinocytosis

8. Exchanges between maternal & fetal circulation – harmful (1) • Thalidomide : treated morning sickness (1950s) • Caused malformations, mental disabilities in newborns • Alcohol: increases miscarriage rates • Damaged placental blood vessels (oxygen supply inadequate) • Nutrient absorption impaired (Vit B6 & Zinc) • Fetal Alcohol Syndrome – growth abnormalities, heart defects, mental retardation

9. Exchanges between maternal & fetal circulation – harmful (2) Smoking: • CO – reduces oxygen carried in the blood • Nicotine – prevents adequate glucose supply • Newborns often small & intellectually poorer

10. Exchanges between maternal & fetal circulation – harmful (3) • Heroin: • Induces temporary relaxed detachment from pain & anxiety – content & sleepy • Leads to dependency & painful withdrawal • Fetus can also get addicted • Vital processes slow down • Mother’s poor health affect baby’s health • Baby often weak & undersized • Withdrawal symptoms – tremors, perspiration, insomnia

11. Exchanges between maternal & fetal circulation – harmful (4) • Rubella: • Similar to measles • Congenital defects in newborns – eyes, ears & heart • HIV: • Virus can cross placenta (30% chance) • Many babies develop AIDS and die early • High termination rate

12. Placental Hormones • During gestation chorionic cell hormones stimulate corpus luteum • Oestrogen & Progesterone secreted = endometrial development • 2 months – placenta takes over (Corpus degenerates) • Oestrogen & Progesterone inhibit FSH & LH • Also stimulate milk-secreting tissue development in breasts • Lactation (milk production) stimulated by prolactin (only produced after birth)

13. Rhesus (Rh) Factor • Rh-ve mother can have a Rh+ve baby • Baby has D antigen – foreign to mother • Initially mother’s immune system unaware • At birth (or miscarriage) maternal blood exposed to fetal blood • Anti-D antibodies produced by mother’s immune system • If pregnant again with Rh+ fetus – fetal red cells attacked • Causes HDNB (Hemolytic Disease of the Newborn) • Treated by massive transfusions • Prevented by anti-D immunglobulin (destroys D antigens)