Development
A. Development during pregnancy
1. Fertilization
2. Formation of the morula
3. Development of the
blastocyst
4. Implantation
B. Embryonic development
1. Beginnings of organ
systems
2. Embryonic membranes
3. Placenta and umbilical cord
C. Fetal growth
D. Hormones of pregnancy
E. Partuition and labor
F. Adjustments of the infant at
birth
1. Respiratory system
2. Cardiovascular system
G. Physiology of lactation
What is pregnancy (gestation)?
– 266 days (lasts from conception to childbirth)
– (gestation calendar 280 days (40 weeks) from 1st day of LMP)
What is fertilization?
– Union of sperm and egg
How many sperm reach the ovum?
– (2,000 – 3,000) out of 300 million in ejaculate reach the ovum vicinity
Where and when does fertilization occur?
– Arrive within 5 – 10 minutes of ejaculation?
– fertilization occurs in ampulla of oviduct
Factors that affect sperm
movement towards the ovum
1.
2.
3.
4.
5.
lashing of tails (flagellum)
guided by strands of cervical mucus
prostaglandins in semen
uterine tenting and contractions
chemical attractant from the ovum?
What is capacitation?
requires ~10 hours
female fluids remove cholesterol from sperm
membranes
sperm membrane becomes more fragile
Viability of sperm
- 6 days in female reproductive tract
“window of opportunity” = a few days before
ovulation to 14 hr after (causes it takes another 10
hours for capacitation) (Margin of error does exist)
Fertilization
1. acrosome reaction
hyaluronidase and acrosin
2. barriers
a. corona radiata
b. zona pellucida
c. egg cell membrane
3. genetic events
4. zygote
5. blocks to polyspermy
(fast vs. slow)
Cleavage
1. blastomeres
- Zygote to 16 cells
2. morula
-free in uterus 4-5 days
- 100 cells
3. blastocyst
a. trophoblast
b. inner cell mass
c. blastocoel
Lots of mitosis
Implantation
1. occurs 6 days after ovulation
in fundus of posterior wall of uterus
2. trophoblast
-invasion of stratum functionalis

3. accomplishments
- formation of the chorion (fetal placenta)
- human chorionic gonadotropin (hCG) secretion
Summary of Fertilization and Implantation
Stages of Development
Prembryonic Stage (0- 16 days)
Embryonic Stage (16 days to 8 weeks)
Fetal Stage ( 8- 40 weeks)
Embryonic Period
1. weeks 3 – 8 ( 16 days to 8 weeks)
2. gastrulation
3. primary germ layers
a. ectoderm
b. endoderm
c. mesoderm
The Developing Human
Extraembryonic membranes
4 weeks
1.
2.
3.
4.
yolk sac
amnion
chorion
allantois
12 weeks
Extraembryonic Membranes
Placenta and Umbilical Cord
Placenta
1. fetal vs maternal
2. functions
Umbilical cord
1.
2.
3.
4.
2 umbilical arteries
1 umbilical vein
Wharton's jelly
umbilicus
Fetal period (weeks 9 - 38)
Fetal Development and Risk
Hormones of Pregnancy
1.
2.
3.
4.
5.
human chorionic gonadotropin
estrogen
progesterone
human chorionic somatomammotropin
relaxin
Parturition and labor
Uterine Contractility
false labor (Braxton Hicks contractions)
true labor = parturition
Positive Feedback of Labor
begin ~30 minutes apart 
progress to every 1 – 3 minutes
cervical stretch  neuroendocrine reflex 
oxytocin secretion uterine contraction 
more stretch  repeat
1. stage of dilation
2. stage of expulsion
3. placental stage
Respiratory system adjustments
at birth
CO2 accumulates in baby’s blood and
strongly stimulates the respiratory
chemoreceptors
First two weeks 45 bpm, then 12 bpm
Cardiovascular System Changes
at Birth
1.
2.
3.
4.
5.
foramen ovale -->fossa ovalis
ductus arteriosus -->ligamentum arteriosum
ductus venosum -->ligamentum venosum
umbilical vein -->ligamentum teres
umbilical arteries -->median umbilical ligaments
Physiology of Lactation
1. What is lactation?
2. How are the breasts prepared?
estrogens and other hormones causes duct growth and
branching
progesterone causes development of secretory acini
steroids prevent milk synthesis
3. Why do the breasts NOT need to produce
milk until a couple of days after birth?
Infants are born with excess body water and fat
Colostrum(1/3 less fat, and lots of immunoglobulins) secreted
for the first 3 days
placental delivery = no estrogens and progesterone secretion
milk synthesis now begins
Physiology of Lactation
4. What is the neuroendocrine reflex that lactation?
a. Tactile stimulation of areola and nipple causes
b. Sensory input to hypothalamus, leading to
c. Secretion of oxytocin and prolactin from
pituitary gland
(1) Oxytocin stimulates contraction of
myoepithelial cells of mammary glands,
leading to milk letdown
(2) Prolactin stimulates renewed milk
synthesis by mammary gland cells