 Complex combination of chemicals (hormones)  Usually one egg once a month  All about timing!!! › Uterus must be ready when egg gets there in case it was fertilized › If no fertilization, tear down lining of uterus and rebuild for next month

 Three Stages 1. Tear Down 2. Rebuild 3. Extra nutrients/blood for potential baby  No Baby? › Back to #1

 First menstrual blood & tissue  No baby = breaks down lining of uterus  5-7 days of blood/tissue exits body Pre-Ovulation

 Ovulation = Egg released  Temp spikes slightly  Most fertile in next few days! › Able to get pregnant  Egg gets fertilized while traveling through oviduct. Post-Ovulation

 Egg travels through oviduct to uterus  Exits body with blood and tissues during menstruation

 Ejaculation › Release of million sperm are deposited just a few inchesaway from the fallopian tubes..  Sperm to egg, not an easy task › Go wrong direction : 2 paths – only 1 leads to an egg › Get attacked by female’s white blood cells › Acidic environment. › Sperms can be inside 72 hours. › The genetic information is inside the head of sperm.

 Dissolve protective goo surrounding egg  One gets through – enters egg  Instant biochemical change in zygote › No more sperm allowed in because of a protective shield.

When it´s fertilized, it continuous to travel through the fallopian tube to ward uterus. After 30 hours the fertilized eggs divides into two cells and is called an Embryo.

 Endometrium= outer lining of uterus › Becomes placenta  Uses mother’s nutrients  Continues development

 Umbilical Cord › Blood vessels from placenta to baby › Mom’s & baby’s blood do not circulate together!  Can have 2 different blood types  Diffusion

 The embryo grows rapidly: A heart and brain begins to form, eyes appear, the face take shapes, small buds become into legs and arms. Also internal organs: lungs, stomach and liver.

 Baby’s body is “told” by DNA to become either male or female.  “Unused” parts disintegrate  “Used” parts continue development  (see overhead)

 DNA determines baby’s gender  XX = Female  XY = Male  Depends on which egg & sperm get together.  Father determines baby’s gender.

STAGEMAJOR CHANGES 0-4 WEEKS Fertilization occurs, embryo travels through fallopian tubes and implants in uterine wall, brain, ears and arms begin to form, heart forms and begins to beat. 5-8 WEEKS Nostrils, eyelids, nose, hands, fingers, legs, feet, toes and bones begin to form, females develop ovaries, male develop testes. Cardiovascular system is working. About 22mm 9-12 WEEKS Embryo becomes a fetus, penis of males is distinct, growth of chin and other facial structures give fetus a human face and profile. 36mm WEEKS Blinking of eyes, sucking of lips occurs, body begins to outgrow head, mother can feel muscular activity of fetus. 140mm WEEKS Limbs achieve final proportions, eyelashes and eyebrows are present; about 190 mm WEEKS Substantial increase in weight, may survive if born at this stage; skin is wrinkled and red, about 280mm WEEKS Fingernails and toenails are present; about 360mm

 Labor – muscles used to open cervix  Baby flips upside down › Head first! › Feet first = Breech (bad)  Cesarian Section (“C-section”) surgical removal of baby  After baby is born mom delivers placenta (“afterbirth”) that detaches from uterus

 Most nutritious option for baby › Milk changes as baby grows  Antibodies from mom create immunity for baby  Studies have shown correlation between breastfeeding and higher intelligence in baby.  Bond w/baby is stronger

 Two types › Monozygotic  From one egg  Identical › Dizygotic  From two eggs  Fraternal  Not identical

 One zygote  Splits in 2  No one knows why!  Completely random = does NOT run in families  Same exact DNA  Nature’s clones

 2 separate eggs get fertilized with 2 different sperm cells  More than one egg got released during ovulation  Siblings › Can be sisters › Brothers › Brother and sister  Tends to run in families

 Used to be called “Siamese” twins  First well known case was in Siam  Identical twins that never completely separated during development  Sometimes can be separated, depending on what is shared.