I'm confused as to how the partial pressure of nitrogen inhaled from an air tank while scuba diving increases as you descend deeper. Obviously the pressure of the water above you increases the deeper you go. Does this external pressure increase the pressure *inside* your body as well? Is that the reason the partial pressure of nitrogen increases inside your body? Are all your air spaces and blood vessels being squeezed, decreasing the space that the nitrogen you inhale occupies inside your body?