Lecture 20
Pregnancy and Fetal Development
John J. Parrish
Placental Functions
Exchange
Endocrine
Placenta
Chemical Protection
Physical Protection
Placental Functions
Exchange
Endocrine
•Gas
•Transient
•Nutrients
•Estrogen
•Waste products
Placenta
•Progesterone
•HCG
•eCG
•PL
Chemical Protection
•Immunosupression
•Prevents infiltration by
maternal defenses
•Filters toxins
Physical Protection
•Shock Absorber
Similarities in Early Development
MAN
PIG
BIRD
Developmental Features
Developmental Horizons
Mare
Germ layers
13-14
Open neural tube
Fusion of chorioamniontic folds
Cow
Ewe
Sow
Woman
14
20
18
10-14
15-21
17
7-8
13
16
10-14
20
28-35
16
17-18
25
28
42-49
21-28
147-155
112
Heart beat apparent
Limb buds visible
Cotelydons first appear
Eye differentiation
24
24
40
21-22
25
30
30-45
Birth
340
280
266
Critical Organ Systems Develop Early!
Fetal Development in the Human
50
3
30
20
10
Ovulation
0
1
0
0
4
8
12
16
20
24
28
32
36
Age of Fetus (weeks since last menstruation)
40
Weight (kg)
2
Parturition
Length (cm)
40
Rump
Crown
Estimates of Age
• Crown rump length
• Length femur, radius or tibia
• Circumference of head
Factors Influencing Fetal Growth
Genetics
Environment
Fetal Hormones
Species
Mother
Nutrition
Size, Parity
Thyroid
Placenta
Blood flow
Size
Growth hormone
Breed
Litter size
Genotype
Insulin
Factors Influencing Fetal Growth
Genetics
Species
Breed
Litter size
Genotype
Factors Influencing Fetal Growth
Genetics
Species
Breed
Litter size
Genotype
Factors Influencing Fetal Growth
Genetics
Species
Breed
Litter size
Genotype
Factors Influencing Fetal Growth
Genetics
Species
Breed
Litter size
Genotype
Certains lines of animals may
grow faster.
Factors Influencing Fetal Growth
Environment
Mother
Nutrition
Size, Parity
Placenta
Blood flow
Size
Factors Influencing Fetal Growth
Environment
Mother
Nutrition
Size, Parity
Placenta
Blood flow
Size
Factors Influencing Fetal Growth
Fetal Hormones
Skeletal and muscular development
Thyroid
Increased energy substrate availability
and stimulates placental growth
Stimulates fetal growth
Insulin
Growth hormone
Uterine Size Changes During Pregnancy
 Hyperplasia
» Increase in # of cells
 Hypertrophy
» Increase in size of cells
 Stretching
Placenta
Umbilical Vein
Ductus
Venosus
Liver
Portal Vein
Vena Cava
Foramen
Ovale
Left Atrium
Head
and
Heart
Lungs
Right Atrium
Aorta
Tissues
Umbilical Arteries
Ductus
Arteriosus
Weeks of Gestation
Ovulation
Weeks of Gestation
Ovulation
Weeks of Gestation
Ovulation
Progesterone
Maintains
Pregnancy!
Progesterone is Essential To Maintain Pregnancy
Corpus Luteum
Placenta
Species
Gestation
Length
Placental
Takeover
Sow
Cow
Ewe
Mare
Human
3.8 mo
9 mo
5 mo
11 mo
9 mo
3.8 mo(none)
6 - 8 mo
50 d
70 d
60-70 d
Other Species in Which Placenta Does
not Take-over Progesterone
Production
 Bitch
 Queen
 Alpaca, Llama, Camel
 Rabbit
 Goat