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What triggers the cry of a baby when she/he is born, just after leaving the mother’s womb?
Answer 1:

Not every baby cries, but it is probably part of the breathing reflex. This breathing reflex is important. Up until birth, the baby’s lungs have never been inflated. Embryos and fetuses get their oxygen from their mother’s blood. Soon after birth, the supply of oxygen-rich blood from the mother stops. The baby usually starts breathing and crying within about 10-30 seconds. But those first few breaths can be the hardest ones we ever take. Think about blowing up a new balloon. When the sides are stuck together and there’s no air inside, you may not even be able to start blowing it up until you stretch it out a few times by hand. Crying puts a lot more force behind the breathing. Crying and coughing helps newborns get some fluid out of their lungs so that the lungs work better.

The usual stimulus that triggers the reflex is the air temperature. Up until now, the baby has always been at a constant 98.6 oF (37 oC). The sudden change to air that is almost always cooler seems to be enough. Of course, some babies may be born where it’s very hot, or they may not respond to the trigger.

Fortunately, there are several other triggers that will do the trick. Unlike what you may have seen in old movies, doctors don’t usually hit the baby on the backside. Normal gentle handling is usually enough to encourage breathing and crying. Sometimes gently rubbing the back or flicking the feet gently does the trick.

You probably know that we need to breathe in oxygen and breathe out carbon dioxide. Our body usually controls our breathing more by the carbon dioxide build-up than by a lack of oxygen. If the baby isn’t breathing, the carbon dioxide that all of its cells are constantly making will build up in its blood. This sends a signal to the brain to start breathing. The more the carbon dioxide builds up, the stronger the signal is to breathe. You may have felt this if you tried to hold your breath. It’s easy at first. Then you feel like breathing. Then you just have to breathe. Babies also get stronger and stronger messages from their brain that they should be breathing.

Human babies have it easy compared to giraffes. Giraffe mothers give birth standing up. The baby starts its life by falling 2 meters (6 feet) to the ground. They have to be ready to run from predators right away.

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