Download Pregnancy & Development

Pregnancy & Development
Fertilization
Timing (egg “good for 12-24 hours; sperm
“good” for 48-72 hours)
 Oviduct
 Capacitation enables sperm to fertilize
ovum
 Sperm numbers – about 50 “work” on the
egg

Fertilization

Diploid
 Zygote
 Sex determination
 Twins
– Dizygotic (fraternal)
– Monozygotic (identical)
Cleavage

30 hours to 4 days
 Mitosis
 Oviduct
 Morula
Blastocyst Stage

Day 5
 Uterus
 Rearrangement of cells
– Trophoblast cells will become placenta
– Inner cell mass will become fetus

Implantation – day 7 or 8
Gastrulation

Week 2
 Ectoderm – destined to become nervous
tissue and skin
 Mesoderm – destined to become skeleton,
muscles, heart, blood vessels…
 Endoderm – destined to become gut &
lungs
Neurulation

Week 3
 Embryo is 2mm long (pencil eraser size)
 Neural groove
 Neural tube
 Destined to become brain and spinal cord
Organogenesis

Week 4
 Embryo 5 mm long
 All major organs have begun their
formation
 Arm & Leg buds form
 Thalidomide & German Measles examples
of what can go wrong.
Fetus

By end of third month, embryo is distinctly
human
 All major organs are established
 Growth for second and third trimester
Maintenance of Endometrium

Estrogen & Progesterone
 From corpus luteum early
 From placenta later
 Birth control pills
Human Chorionic
Gonadotropin

HCG
 Made by embryo
 2-12 weeks
 Maintains corpus luteum through first
trimester
Placenta

Development begins at 4 weeks and
functional by 12 weeks
 Covers about 1/3 of inner uterus
 Function
– Nutrients
– Waste
– Estrogen & Progesterone
Placenta

Maternal tissue
– Decidua basalis of the endometrium

Fetal tissue
– Chorion which develops from the trophoblast
cells
– Chorionic villi contain capillary beds from
umbilical arteries and vein
Fetal tissue

Umbilicus
 Amnion
 Amniotic fluid
Gestation

280 days
 9 full months
Parturition

Mild contractions due to high levels of
estrogen.
 Once contractions occur every 30 minutes,
labor occurs
 Amniotic fluid released
 Baby’s head serves as a “wedge”
Hormones

Estrogen increases which causes uterine
contractions, then levels drop as parturition
proceeds
 Progesterone levels drop allowing the
uterine contractions
 Local prostaglandins result in contractions
Hormones

Oxytocin causes strong uterine contractions
and works in a positive feedback
mechanism
 Relaxin, made by placenta, dilates cervix,
relaxes symphysis pubis
Afterbirth

10-45 minutes later
 Placenta