Oxygen – you breathe it all day, but what does it actually do?

Oxygen is so normal that we barely think about it.

We breathe all day and assume that once air reaches our lungs, the job is done.

But breathing in is only the beginning.

Oxygen still has to move from the lungs into the blood, travel around the body and reach the places where it is needed.

Most of that journey happens attached to haemoglobin inside red blood cells.

You can think of red blood cells as the body’s natural oxygen transport system.

So what happens next?
Once oxygen reaches our cells, things get more interesting.

Our cells need energy to do their jobs — to move muscles, maintain tissues and keep the body functioning.

A large part of that energy is produced inside structures called mitochondria.

This is where oxygen helps the body produce ATP — the usable energy our cells rely on.

So, very simply:

you breathe → oxygen enters the blood → it reaches your cells → it helps them produce energy

And this is happening constantly.

But there is a catch
It is easy to think:

“If oxygen is so important, then more oxygen must always be better.”

Not exactly.

In a healthy person, haemoglobin is already usually carrying close to the amount of oxygen it can hold.

So taking a few deeper breaths does not suddenly flood the body with huge amounts of extra oxygen.

And this is where it gets interesting.

Because there is something that can change the way oxygen behaves in the blood.

Pressure.