Chapter 7 Fetal Growth and Development

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Transcript Chapter 7 Fetal Growth and Development

Chapter 7
Fetal Growth and Development
인제대힉교 부산백병원
산부인과학 교실
R1 서 영진
The maternal organism responds passively
to signals emanating from embronic-fetal
and extraembryonic tissues
The conceptus is the dynamic force in the
pregnancy
Essential for successful pregnancy
-implantation, maternal recognition of
pregnancy, immunological acceptance,
endocrine function, nutrition, parturition
Determination of gestational age(1)
Gestational age (or menstrual age)
from the 1st day of the last menstrual period
:2 weeks before ovulation & fertilization
3 weeks before implantation of the blastocyte
Ovulation age
:the time of ovulation
Postconceptional age
:the time of conception-nearly identical
Determination of gestational age(2)
Calculate gestational age
:the 1st day of the LMP~the birth of the fetus
:280 days=40 weeks=9 1/3 calendar months
(10 units of 28 days)
A quick estimate of the EDC
:LMP +7 days
-3 months
Trimester
:3 units of 3 calendar months each
Morphological growth(1)
Ovum, zygote, and blastocyst
:during the first 2 weeks after ovulation
Morphological growth(2)
Embryo
(the 3rd weeks after fertilization)
-most pregnant test: hCG (+)
-embryonic disc: well defined
-chorionic sac: 1 cm
·The end of the 4th week
-embryo: 4~5 mm
-chorionic sac: 2~3 cm
-primitive heart (the middle oh the 4th week)
-arm & leg buds
-amnion is beginning
Morphological growth(3)
·The end of the 6th week
-embryo: 22~24mm
-head > trunk
-heart : completely formed
-fingers & toes
-the arms bend at the elbow
-upper lip
-external ears
Morphological growth(4)
Fetus
(occur 8th weeks after fertilization)
-the embryo-fetus: nearly 4 cm
-the major portion of lung
·12 gestational weeks
-uterus: palpable above the symphysis pubis
-crown-rump length (CRL): 6~7 cm
-center of ossification
-fingers & toes: differentiated
-skin & nails: developed
-external genitalia: beginning
-spontaneous movement
Morphological growth(5)
·14 gestational weeks
-gender can be correctly determined
·20 gestational weeks
-skin:
less transparent, lanugo covers
-scalp hair
·24 gestational weeks
-skin: wrinkled, fat deposition
-eyebrows, eyelashes
-the bronchi, bronchioles, alveolar duct
(the terminal sac required for gas change has not yet formed)
Morphological growth(6)
·28 gestational weeks
-skin: red & covered with vernix caseosa
-moves energetically, cries weakly
-90% chance of intact survival
·36 gestational weeks
-skin: rotund
-excellent chance of intact suvival
·40 gestational weeks
-fully developed
Morphological growth(7)
Length of fetus
-crown-rump height: the variability in the length of
the legs and the difficulty of maintaining them in
extension
-the length is a more accurate criterion of
gestational age than weight
Morphological growth(8)
Weight of the newborn
-boys > girls (100g, 3 oz)
-depend on race, parental economic status, size of
the parents, parity of the mother, and altitude
-the second half of pregnancy ~ the 37th week
:increases in a linear manner
Morphological growth(9)
Morphological growth(10)
Morphological growth(11)
Molding
-the bones of the cranium are normally connected
only by a thin layer of fibrous tissue which allows
considerable shifting or sliding of each bone to
accommodate the size and shape of the maternal
pelvis
-the location of these fontanels gives important
information concerning the presentation and
position of the fetus
Morphological growth(12)
Fetal brain
-myelination of the ventral roots of the cerebrospinal
nerves and brain stem: begins at 6 months
-the major portion of myelination: after birth
The fetal-maternal communication
system: placental arm(1)
Mother→fetus: oxygen, nutrient
Fetus→mother: carbon dioxide, metabolic wastes
Maternal blood: in the intervillous space
Fetal blood: in the fetal capillaries in the intravillous
space of chorionic villi
no direct communications between
the fetal blood
As lung, gastrointestinal tract, kidney
The fetal-maternal communication
system: placental arm(2)
The intervillous space: maternal blood
-the residual volume of the intervillous space of the
term placenta: 140ml
-the normal volume of the intervillous space before
delivery: 280ml
-uteroplacental blood flow near term: 700~900ml/min
-blood pressure of intervillous spac <uterine arterial pressure
>uterine venous pressure
- uterine venous pressure↑: intervillous space pressure↑
(supine, standing position)
The fetal-maternal communication
system: placental arm(3)
Fetal capillaries of the intrevillous space: fetal blood
-during normal labor, the rise in fetal blood pressure must be
parallel to the pressure in the amnionic fluid and the
intervillous space
-otherwise, the capillaries in the chirionic villi would collapse
Placental transfer(1)
Chorionic villus
-the pathway from mother to fetus
(1) syncytiotrophoblast
(2) stroma of the intravillous space
(3) fetal capillary wall
-after midpregnancy
(1)Langhans cell, cytotrophoblast ↓
(2)villous epithelium : syncytiotrophoblast
(3)villous capillary : thinner
(4)fetal vessel increase
-total surface area of chorionic villi : 10 m2
→correlation with fetal weight
Placental transfer(2)
Regulation of placental transfer
-the concentration of the substance in the maternal plasma,
which it is bound to another compound, such as carrier protein
-the rate of maternal blood flow through the intervillous space
-the area available for exchange across the villous trophoblast
epithelium
-the physical properties of the tissue barrier (ex. diffusion)
-the capacity of the biochemical machinery of the placenta for
effecting active transfer (ex. specific receptor)
Placental transfer(3)
-the amount of the substance metabolized by the placenta
during transfer
-the area for exchange across the fetal capillaries in the
placenta
-the concentration of the substance in the fetal blood
-specific binding or carrier proteins in the fetal or maternal
circulation
-the rate of fetal blood flow through the villus capillaries
Placental transfer(4)
Mechanism of transfer
-molecular weight is clearly important in determining
the rate of transfer by diffusion
-the smaller, the more rapid
-simple difussion: oxygen, carbon dioxide, water,
and most(but not all) electrolyte
-slow rate: insulin, steroid, thyroid hormone
-high molecular weight, but transverse: Ig G
(specific receptor)
Placental transfer(5)
Transfer of oxygen & carbon dioxide
-the placeta served as the lung
-carbon dioxide: diffusion limited
oxygen: blood-flow limited
-8mL O2 /min/ kg of fetal weight
but, store for only 1 to 2 min
so, this supply must be continuous
Placental transfer(6)
-oxygen saturation of intervillous space: 65 ~75%
partial pressure: 30 ~35 mmHg
-the fetus normally does not suffer from lack of O2
cardiac output: greater
oxygen-carrying capacity of fetal Hb: high
Hb concenturation; high
-carbon dioxide: more rapidly by diffusion
fetal blood has less affinity
Placental transfer(7)
Selective transfer and facilitated diffusion
-ascorbic acid : simple diffusion
-iron : unidirectional treasfer
-infection: viruses, bacteria, and protozoa
(rubella, varicella, CMV, HIV, treponeme
tuberculosis)
-rarely, malignant cell
Nutrition of the fetus(1)
-because of the small amount of york, development
is dependent on nutrients obtained from the mother
-so, indigested foodstuff is translated into storage
forms: liver, muscle, adipose tissue
-glucose→glycogen in liver & muscle
amino acis: protein
storage of the excess as fat: peaks in 2nd trimester
-during fasting: glycogen, adipose tissue(fatty acid)
(by glucagon, norepinephrine, hPL,
glucocorticosteroid, thyroxine)
Nutrition of the fetus(2)
glucose and fetal growth
-gucose is a major nutrient for fetal growth & energy
-hPL: promote the mobilization and use of fatty acid
blocks the peripheral uptakes and use
of glucose
glucose transport
-by a carrier mediated, stereoapecific, nonconcentrating process of facilitated diffusion
Nutrition of the fetus(3)
glucose transport protein
-six separate glucose transport protein (GLUT) have
been discovered
-GLUT-1 & GLUT-3 in plasma membrane(microvilli)
of syncytiotrophoblsst
glucose, insulin, and fetal macrosomia
-hyperinsulinemia, IGF-1, IGFBP-3, FGF-2,
increased GLUT protein expression: macrosomia
Nutrition of the fetus(4)
free fatty acids and triglycerides
-triacylglycerols does not cross the placenta
but, grycerol does
-most fatty acids cross the placenta by simple
diffusion
-the apoprotein and cholesterol ester of LDLare
hydrolyzed by lysosomal enzyme in the syncytium
to give:cholesterol for progesterone stnthesis
free amino acid-including essential amino acids
essential fatty acids, primarily linoleic acid
Nutrition of the fetus(5)
Amino acids
-in addition to the hydrolysis of LDL, the placenta is
known to concentrate a large number of amino
acids intracellularly
Proteins
-Ig G: Fc receptor on trophoblast, cross the placenta
same concentration in cord & maternal area
-Ig M: increase-fetal infection (immune system)
Nutrition of the fetus(6)
Ions and trace metals
-iodide transport across the placenta
carrier mediated, energy-requiring avtive process
-zinc : fetus > mother
-copper : fetus < mother
Nutrition of the fetus(7)
Placental sequestration of heavy metals
-metallothionein-1: heavy metal binding protein
(zinc, copper, lead, cadmium)
-smoker: cadmium ↑- metallothionein↑ - copper
binding – pseudo copper deficiency
→collagen ↓ :rupture of membrane
Nutrition of the fetus(8)
Calcium and phosphorus
-actively transported from mother to fetus
-PTH-rP:fetal parathyroid, placenta, tissue, decidua,
myometrium
adenyl cyclase activation
calcium movement
Nutrition of the fetus(9)
Vitamins
-Vit. A (retinol): fetus > mother
bound retinol-binding protein
across the syncytium
-Vit. C(ascorbic acid): energy dependent
carrier mediated
-Vit. D(cholecalciferol) : fetus < mother