Big brain evolution: orchestrating a first breath (Evolution)

by David Turell , Monday, June 05, 2023, 22:53 (326 days ago) @ David Turell

Several forces at work:

https://www.nationalgeographic.com/premium/article/mermaids-womb-placenta-uterus-breath...

"An intricate choreography of physiological and molecular events quickly unfolds to help the newborn babies to draw their very first breath, generally within about 10 seconds after delivery. "It's one of the most fundamental events that a person has to take," says David Tingay, a neonatologist at The Royal Children’s Hospital at Melbourne, Australia.

"This first breath marks the crucial step towards the transition from fetal circulation to independent respiration.

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"At around the fourth to fifth week of gestation, the respiratory system of the fetus starts to form as a buds of tissue separate from the primitive foregut and develop into the lungs. By the end of the eighth week, the basic architecture of lung is established, and throughout subsequent weeks and months, the lung tissue grows and matures. By the time the pregnancy reaches full term at nine months, the fetus’ lungs are complete and almost ready to inhale and exhale outside the womb.

"But in the womb the fetal lungs are filled with fluid. This liquid—secreted by the lungs—provides cushioning and protection for the developing organs, helping to prevent compression or damage.

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"Since the fetus depends entirely on the placenta for vital nutrition and oxygen, the fluid-filled fetal lungs remain inactive, waiting to spring into action within seconds before and after birth.

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"The fetus begins to make some breathing movements as early as about 10 or 12 weeks. These increase during development so by the full 40 weeks of gestation the baby is prepared to breathe outside of the womb.

"'But the fetus does not yet actually breathe anything at that time," says neonatologist Caraciolo Fernandes. Instead, fetal breathing movements train the fetus to use the respiratory muscles, develop the lungs and neural circuits of respiratory control, to be ready at the birth.

"As the baby travels through the birth canal, the compression squeezes some of the fluid from the lung. The pressure changes during birth and hormonal shifts in the baby also initiate absorption of the lung fluid. Once the baby is delivered, the abrupt drop in temperature—from inside the womb to the outside world— the physical stimulus of cold air on the skin, and the glare of bright light within seconds after birth triggers a gasp of air as the baby takes its first breath.

"'The fetal lungs act like a big sponge that suddenly fill-up with little air spaces," says Tingay. "That's what babies do in their very first breath."

"The pressure caused by the influx of air at the first breath pushes the remaining fluid out of lungs.

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"When the lungs open, the air fills the spaces and help the organs to displace and absorb the last bit of fluid, says Fernandes. Any residual fluid that remains is either expelled through coughing or gradually absorbed into the bloodstream and lymphatic system.

"Along with the neural stimuli that activate the breathing in a newborn, some specific genes also get turned on at birth. As mice are born, neurons release a neurotransmitter called PACAP that regulates breathing. Another study in mice reveals that a gene called Foxa2 is required for transition to breathing air at birth."

Comment: mammalian birth is a beautifully choreographed adaptive event of which first breath is a very important part. Physico-chemical and hormonal all at once. So many parts acting at once must be a designed mechanism.