Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: lyner on 28/10/2008 14:38:18
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I was talking to a Medic about my newborn Grandaughter and, as with many babies, she exhibited a hint of jaundice.
He pointed out that the haemoglobin in foetal blood is different from the haemoglobin needed for breathing air.
The difference in oxygen concentration across the placental barrier is lower than the difference in concentration in the lungs. Consequently the haemoglobin has to take up Oxygen more readily before birth than after.
I thought that was a really cool bit of engineering!
The baby needs to change its blood chemistry pdq and that is why they sometimes show jaundice very soon after birth.
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Yeah, it's fiendishly clever that, isn't it? They have haemoglobin that grabs onto the oxygen really hard when they're in the womb because that's the only way of getting it out of mum's blood, but it actually doesn't really give up its oxygen load as readily as it needs to when it gets to the rest of the body tissues so once the sprog is out in the big wide world it needs a complete new set of red blood cells that strike the right balance.
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Congratulations sophicetaur on the birth of your granddaughter, hope you enjoy being a granddad as much as I do.
My grandson was 6 weeks premature and also had jaundice, now I know why!
He was placed in an incubator for a few weeks under special lighting and he's now 3 months+ and perfectly healthy.
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Good news all round then!
Plus we learned something interesting.
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Yes, this is clever, but it's not the reason why a newborn is prone to jaundice. This is a common myth.
The transition from foetal to adult-type haemoglobin does occur around the time of birth, but the reason for neonatal jaundice is that prior to birth excess bilirubin produced by the destruction of senescent (old) red cells was shunted to the maternal circulation across the placenta for processing by the mother's liver. But post-partum the baby no longer has this facility and has to stand on its own two metabolic feet. Consequently, any short-fall in liver processing power is reflected in a slight excess of bilirubin in the bloodstream for a few days, triggering jaundice. This is dealt with by exposure to sunlight or, more correctly, light containing blue wavelengths. Bilirubin is photolysed (broken apart) by blue light, yielding a more soluble form of the molecule which can be excreted in urine rather than by the liver. This is why phototherapy is so effective at treating the problem.
Chris
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That all fits in now. Thanx Chris.
Another cleverness in the placenta!
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Thanks for the correction as I thought the blue light was to produce vit D as in sunlight exposure.
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Vit D synthesis needs near UV light, not blue.
I can underestand how being born (and therfore having a much greater oxygen supply ) could trigger a switch from production of fetal to adult haemoglobin, but does anyone know if this speculation of mine is right?
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I'm not sure what the trigger is for HbF to HbA switch, but I don't think it's oxygen; babies' bodies "know" their developmental stage (that's partly how they "know" to be born at 40 weeks). The placenta is also highly metabolically active and produces a number of important endocrine signals. Once a baby is born this signal source is lost, hence there are manifold ways in which the baby can alter its gene expression.
Chris
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Could the trigger be C02? as I believe its that that causes you to take a breath. An infants lungs in the womb produces no C02 then as soon as its born the build up of C02 triggers breathing.
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Congratulation lyner