Pregnancy and Fetal Development
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Placental Functions
- exchange
- gasses, nutrients, waste products
- chemical protection
- immunosupression, protects infiltration by maternal defenses,
filters toxins
- physical protection
- endocrine
- transient - estrogen, progesterone, HCG, eCG, PL
Fetal Development
- simalarities
- all look similar at early stages, not until fetal stage do
they begin to differ
- landmarks in development
- major organ systems develop early
- gross changes in size
- length increases before weight
- at end of gestation weight is increasing rapidly
- energy demands of the fetus increase most rapidly toward
the end of gestation
- estimates of fetal age
- crown-rump length
- length of femur, radius or tibia
- circumference of the head
- factors effecting fetal growth
- genetic
- species, breed, litter size, genotype
- environment
- mother (nutrition, size, parity), placenta (blood flow, size)
- fetal hormones
- thyroid, insulin, growth hormone
Uterine growth and distention
- hyperplasia - increase in the number of cells
- hypertrophy - increase in size of cells
- stretching
Fetal Blood Flow
- Ductus venosus - shunts around the liver
- Ductus arteriosus - shunts from pulmonary artery to aorta (bypasses lung)
- Foramen Ovale - shunts from right atrium- vena cava to the left atrium (bypasses
lung)
Hormonal Changes During Pregnancy (see text Figures 14-4,
14-5, 14-6, 14-7 and 14-9)
- Progesterone
- present throughout gestation
- in mare, eCG causes formation of accessory CL which produce
progesterone
- Estrogen
- increases toward the middle to end of gestation
- Placental Lactogen
- in cow, ewe, human
- not found in the mare or sow
- somatotrophic - growth promoting
- lactogenic - promotes growth of mammary gland in the mother
Progesterone Needed to Maintain Pregnancy
- Initially progesterone from CL
- Depending on species, the placenta can takeover progesterone
production (see text Table 14-1)
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