Foetal Preparations for Birth & Foetal Programming

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  • Created by: Becca
  • Created on: 29-12-13 22:42
Which factors influence foetal growth?
Foetal genome (modulated by fetal & maternal factors/imprinting), maternal height linked to uterine capacity & potential for growth, maternal nutrition, placenta malfunction may restrict growth & fetal sex (males weigh more than females)
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What is the role of insulin-like growth factors (IGFs) in foetal growth?
Produced by foetal cells, IGF2 (paternally expressed) stimulates placental growth & transport mechanisms, synthesis 2/3x higher. IGF1 sensitive to nutrient levels/insulin/thyoxine/glucocorticoid thus matches foetal growth to maternal nutrient supply
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What is the O2 & CO2 composition of maternal and foetal blood?
PO2 in umbilical vein low relative to PO2 in maternal blood, gradient exists, O2->fetus. PCO2 high in UA/UV, CO2->maternal side. O2 saturation high in fetus, much lower O2 tension still leads to a similar O2 content. High foetal O2 trapping property
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What are the oxygen trapping properties of foetal blood?
Foetal Hb has 2 alpha, 2 gamma globin chains, gamma has no 2,3-DPG binding site, HbF has higher affinity, bind more O2 -> high O2 saturation. Double Bohr effect: maternal pH falls due to uptake of fetal CO2 drives release of maternal oxygen
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What happens in the foetal cardiovascular system?
2 fetal ventricles pump in parallel, 3 shunts (ductus venosus/arteriosus, foramen ovale) divert blood away from lungs & towards placenta. After coursing through the descending aorta, blood flows towards the placenta in two umbilical arteries
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What does the ductus venosus do?
Oxygenated blood returns in umbilical vein, carried into 2 channels. The larger ductus venosus bypasses hepatic circulation, delivers blood directly to IVC. Small amount enters liver sinusoids & mixes with portal circulation, sphincter regulates flow
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What does the foramen ovale do?
IVC carries blood to right atrium, splits into 2 streams by crista dividens which projects from foramen ovale in inter-atrial wall. The larger stream passes through the foramen ovale into left atrium, avoiding pulmonary circulation
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What does the ductus arteriosus do?
The smaller stream continues through right atrium to right ventricle & out through pulmonary artery. Splits to 2 channels, largest passes through 3rd shunt, ductus arteriosus, to carry blood to aorta. The smaller channel takes blood to foetal lung
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What cardiovascular changes happen at birth?
Closure of umbilical arteries/vein/ductus venosus/arteriosus. Inflation of lungs, dramatic fall in pulmonary vascular resistance, rise in pulmonary outflow. Reversal of inter-artial pressure, flap in foramen ovale closes, heart pump can act in series
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What foetal respiratory changes happen to prepare for birth?
Surfactant produced 2 months before birth, reduces surface tension, prevents collapse of alveoli in expiration. Foetus makes rapid respiratory movements before birth, moves amniotic fluid in/out of lungs, removal of fluids through mouth in delivery
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What foetal renal changes happen to prepare for birth?
Kidneys are functional during pregnancy and produce substantial quantities of hypotonic urine. Tubules are inefficient at sodium reabsorption. Fetal urine contributes to total amniotic fluid (0.5 L/day)
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What foetal nervous system changes happen to prepare for birth?
Responsive to external stimulus (loud noises/intense light/rapid fall in temp) from mid 2nd trimester. Sensory impulses (pain) can't be detected before week 29 of gestation
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What is the Barker hypothesis?
Relationship between birth weight & lifetime risk for CHD. The lower the weight of a baby at birth and during infancy, the higher the risk for coronary heart disease in later life. Low birth weight associated with raised risk high BP/stroke/type 2 DM
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What evolutionary advantages have developed to help low birth weight babies to survive?
Select genes that reduce fetal growth in response to poor maternal nutrition to prepare offspring for optimised survival in a resource-poor world. But if postnatal world is nutritionally rich, catch-up growth predicts poorer middle age health
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What is the thrifty gene hypothesis?
Explains prevalence of obesity & diabetes in modern society. Previously genes that promoted efficient fat deposition would be advantageous for famine, but in modern society these genes are disadvantageous as famine never comes -> obesity & diabetes
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What are epigenetics & epigenome?
Epigenetics: The mechanisms of regulating gene expression without altering the DNA sequence itself. Epigenome: the machinery that regulates gene expression and thus may alter phenotype
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What do epigenetic modification to chromatin occur through?
DNA methylation, histone modification & chromatin remodelling through non-coding RNAs
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What is parental imprinting?
For most genes expression in biallelic. For a subset of genes one parent actively silences their own gene so there is a parent-of-origin specific monoallaelic expression e.g. paternal expression of IGF2 ensures optimal nutrition for foetus
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What is altruism?
A behaviour benefiting another individual which incurs a direct cost for the individual performing the altruistic action
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What mother-offspring conflict is an examples of altruism?
Nutrient transfer reduces fitness of mother whilst increasing fitness of foetus. Placental tissue which is fetal will and does express mechanisms that increase nutrient flow from mother (creates conflict)
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Card 2

Front

What is the role of insulin-like growth factors (IGFs) in foetal growth?

Back

Produced by foetal cells, IGF2 (paternally expressed) stimulates placental growth & transport mechanisms, synthesis 2/3x higher. IGF1 sensitive to nutrient levels/insulin/thyoxine/glucocorticoid thus matches foetal growth to maternal nutrient supply

Card 3

Front

What is the O2 & CO2 composition of maternal and foetal blood?

Back

Preview of the front of card 3

Card 4

Front

What are the oxygen trapping properties of foetal blood?

Back

Preview of the front of card 4

Card 5

Front

What happens in the foetal cardiovascular system?

Back

Preview of the front of card 5
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