Body adaptation during free-diving

When you dive you body will eventually adapt to the new more pressurized environment:

1 - A drop in the heart rate (...see reflex bradycardia)

2 - Your blood will have more red cells carrying oxygen (...see splenic contraction)

3 - Your blood vessels will shrink, leading away oxygen that benefits vital organs (...see vasoconstriction)

4 - Blood plasma will fill up blood vessels in the lungs and reduce residual volume. Without this adaptation, the human lung would shrink and wrap into its walls, causing permanent damage, at depths greater than 30 meters.