1. Human Development

2. Week 0 – Start of Menstruation & Follicle development
Pregnancy is always backdated to the start of menstruation
At this point in time, several follicles will start to develop.
Primordial (ones in arrested development since before birth)  primary follicle (single layer of cells)  secondary follicle (several layers of support cells)  tertiary (Graafian) follicle that has a large nutrient-filled space called the antrum – this is the type that will be ovulated. Others, disintegrate.
A woman at puberty has ~400,000 oocytes, of which she will release less than 500 ova.

3. Week 2: Fertilization
After ovulation, the egg travels to the fallopian tube, where it remains viable for 24 hours.
Sperm travel up the vagina, through the cervix, through the uterus, and into the fallopian tubes to meet the egg.
Sperm are attracted to chemicals released by the egg
Many sperm surround the egg, and attempt to penetrate the oocyte. Fertilization occurs when one sperm penetrates the egg to form a fertilized egg, or zygote.
Fun fact
There are roughly 250 million sperm per ejaculation … only one of which will bind with an egg.

4. Week 3: Cleavage & Differentiation
It takes about 3 days for the zygote to reach the uterus
During this time, the zygote divides (cleaves) many, many times, forming a hollow ball of undifferentiated cells called a blastula.
The blastula releases human chorionic gonadotropin (hCG) which tells the woman’s body to maintain the endometrial lining.
During gastrulation, the cells begin to differentiate: some layers will give rise to different body systems in the embryo, other layers will form the placenta and umbilical cord.
At the blastula stage, cells are completely undifferentiated. Cells can be plucked off for genetic analysis without damaging the embryo. Division of the embryo at this point in time produces identical twins.
Pregnancy tests measure hCG

5. Week 4: Implantation
The blastula starts to burrow into the endometrial lining around week 3, and this process is completed in week 4. One endometrial tissue has completely grown over the embryo, it is said to be implanted.
By week four, the blastula has a begun to develop a placenta that exchanges nutrients, oxygen, and wastes with mother’s blood supply
This is when a women can first learn she is pregnant!
Watch me!

6. Weeks 5-8: Embryonic Development
The embryonic period is the most sensitive time of development. Toxins, disease, drugs can damage the embryo.
All body systems are –more or less – formed by 8 weeks gestation.
Heart is beating since week 6

7. Weeks 9-12 (third month)
From now until birth the baby is called a fetus.
Organs continue to develop.
Fetus begins producing blood
Gender observable

8. Weeks 17 - 20 (fourth month) Face is more human like
Kidneys begin to function

9. Weeks (fifth month)
Vernix caseosa (waxy coating) and lanuga (fine hairs) covers skin
Fetus is very active, and mother can start to feel movements
Fetus practices sucking and swallowing
Fetus can hear

10. Weeks 26 – 30 (seventh month)
Weeks (sixth month)
Weeks 26 – 30 (seventh month)
Baby begins rapid weight gain; nerves become myelinated; lungs begin to develop
Earliest premature babies every to survive at 22 weeks.
A baby born at 25 weeks gestation who receives extensive medical help has about 50% chance survival. This number goes up with every week – even every extra day – of gestation.

11. Weeks 31 – 35 (eighth month) Weeks 36 – 40 (ninth month) Just for fun!
By 35 weeks, no real difference in survival, between pre- and full-term, though some respiratory and feeding care may be needed.
Baby continues to gain fat, and nervous system better regulates the fetus, creating patterns of waking and sleeping.
Just for fun!

12. Childbirth Hormones
In the days leading up to childbirth, progesterone levels fall and estrogen levels rise.
Two other hormones are also produced: oxytocin and prostaglandins.
more uterine contractions, and ‘softening’ of the cervix
True labor begins when contractions become regular and increase in intensity. Starts a positive feedback loop
contractions  oxytocin release  contractions  oxytocin release
Aspirin and ibuprofen are antiprostagladin drugs and may inhibit labor
Some hormones are produced by baby, others by mom – initation of labor involves both!

13. Stages of labor Dilation Expulsion Placental Stage
Contractions push baby’s head against cervix and also pull on the cervix, causing it to soften and open up to 10 cm.
Longest lasting stage 6 – 12 hours, or many many more.
Rupture of amniotic sac (breaking the water) occurs at during this stage
Expulsion
Woman actively pushes the baby out
Lasts 30 min – 2 hours
Head comes out first, and doctors suction out baby’s mouth immediately
Placental Stage
~15 minutes after the baby is born, the placenta is expelled.
Aspirin and ibuprofen are antiprostagladin drugs and may inhibit labor
Some hormones are produced by baby, others by mom – initation of labor involves both!
A not-so-bad animation …
50 min NOVA show