Tuesday, August 23, 2016

Drawing Life from Death

(except from  The Spark Of Life , Electricity in The Human Body, by Frances Ashcroft) [Time 8:23AM, 24/08/2016, counter @ 2088 3098]

Aya Soliman had a most unusual start in life, being born by Caesarean section two days after her mother Jayne was declared brain death.
Jayne, a champion ice skater, had a fatal brain haemorrhage when she was twenty-five weeks pregnant. She was flown by air ambulance to hospital in Oxford, but died shortly after arrival .
Although Jayne's brain was dead, doctors decided to keep her body alive to provide vital time for her daughter's lungs to mature.

Within the womb, the fetus floats in a cushioning sac of water. Its developing lungs are filled with fluid and it does not breath air, but obtains all the oxygen it needs via the umbilical cord that links it to the placenta. At birth, the water withing the lungs must be rapidly removed as the newborn child switches over to breathing air.This is achieved with the help of specialized epithelial sodium channels (ENaC channels) that are present in the cells that line the lung.
At birth the ENaC channels open, allowing sodium ions in the lung fluid to flow down their concentration gradient into the lung cells. because sodium ions  drag water with them, the lungs quickly dry out and so long as ENaC channels are present and functional, the lungs are rapidly cleared of fluid. Without ENaC, however, babies are at risk of drowning in their own fluid at birth, and may suffer from 'wet' lung.

During normal development ,  a rise in  steroid hormones switches on ENaC production a few weeks prior to birth, ensuring the lungs are fully mature when the baby  is delivered.
At twenty-five weeks of pregnancy, however, lung development is incomplete and the number of ENaC channels in the cells lining the lung is still very small. A chemical called surfactant that reduces the surface tension of the tiny air sacs in the lungs and so prevents their collapse is also low. Thus if a baby must be delivered early, and conditions permit, steroids are administered to the mother before birth. These cross over the placenta and help her premature baby's lungs mature. As a mother's womb is the optimal incubator for a baby, Jayne's body was kept alive (but brain death) on a life-support machine while steroids were given to provide her daughter with the best possible chance of life.

There is a further twist to this story. It turns out that at birth ENaC channels are stimulated to open more completely by stress hormone adrenaline, which rises dramatically in the mother's blood during the trauma of labour. This may explain why babies born by Cesarean section, where this stimulus is lacking, may have more difficulty clearing their lungs than those born naturally, and why they experience a higher incidence of respiratory complications in the postnatal period.

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