SIZING IT UP

How big are the body parts you can’t see?

WHEN we are born, our brains weigh just less than a pound. By the time we reach adulthood, they weigh around 3lb and are 16cm long.

This may sound compact for the organ that controls everything we do, but its folded structure makes the very best of the available space — when flattened out, its total surface area is between 1,500cm and 2,500cm squared.

The lungs also have a huge surface area. The lining is covered in 600million tiny air sacs called alveoli, which, when flattened out, give your lungs a total surface area of 50m to 75m squared.

The right lung is wider and shorter than the left, to leave space for the liver. Together, they weigh around 1.3kg.

But there are significant gender discrepancies: at rest, a male lung holds 1.5 pints of air, while female capacity is around 0.8 pints.