Trace molecule of oxygen from the external nares to the pulmonary capillaries of the lungs?

nose - nasal cavity - larynx - trachea - primary bronchus - secondary bronchi - tertiary bronchi - terminal bronchi oles - respiratory bronchioles - alveoli - alveolar sacs

the alveolar sacs contain the pulmonary capillaries. the actual gas exchange occur here by simple diffusion. O2 goes from the lungs into the O2 depleted RBC.