1. Fertilization & Pregnancy
Campbell pages

2. Quick Recap http://pennhealth.com/health_info/pregnancy/000078.htm
Egg production
Sperm production
Conception

3. Fertilization
Sexual intercourse; millions of sperm are ejaculated into a female’s vagina
Sugar in ejaculate  fuel for the “journey”
Some sperm find their way through the cervical opening  uterus  fallopian tubes
Typical location of fertilization is fallopian tube
Gametes fuse together

4. Cortical Reaction
When the two gametes fuse, cortical granules (on the oocyte) release enzymes
These enzymes cause a chemical change in the zona pellucida (ovum layer)
Makes it impermeable to any more sperm
Happens in a few seconds
This ensures only one sperm cell fertilizes the oocyte
Why is this important?
Fertilized ovum = zygote

5. Human gestation Pregnancy is preceded by conception
Averages 266 days (38 weeks) from conception or 40 weeks from the start of the last menstrual cycle
Trimesters
Body size and extent of development determine length of gestation
Elephants: 600 days (yikes!)
Rodents: 21 days

6. First Trimester Organogenesis Development of organs
Heart beats ~4 weeks
End of 8th week: major structures in rudimentary form
Most sensitive to drugs and radiation
Birth defects

7. First Trimester (cont.)
Embryo secretes the hormone human chorionic gonadotropin (HCG)
Maintains secretion of progesterone and estrogen by the corpus luteum (without it, menstruation and spontaneous abortion of the embryo would occur)
Levels of HCG are so high some is excreted in the urine (pregnancy tests)
High levels of progesterone initiate:
Increased mucus in the cervix (protective plug)
Growth of the placenta
Enlargement of the uterus
Cessation of ovulation and menstrual cycle
Breasts enlarge

8. Development of the Placenta
4th week
Organ that contains embryonic and maternal blood vessels
Umbilical cord
At no time does blood from the fetus and mother exchange; there IS exchange of materials, but NOT blood

9. Exchange within Placenta
Materials passed from fetus to mother
Materials passed from mother to fetus
Carbon dioxide
Oxygen
Urea
Nutrients (glucose, amino acids)
Water
Hormones (HCG)
Hormones
Vitamins, minerals
Alcohol, drugs, nicotine, some viruses

10. Second Trimester The fetus grows rapidly to ~30 cm and is very active
Hormone levels stabilize as HCG declines
Corpus luteum deteriorates
The placenta secretes its own progesterone (which maintains the pregnancy)
Switch is a pivotal time
Women start to show

11. Third Trimester Rapid growth Fetal activity decreases
~3.5 kg, 50 cm
Fetal activity decreases
Mothers abdominal organs become compressed and displaced
The need to urinated frequently, back pain, indigestion