Final answer:
Oxygen travels from the nose through the pharynx, larynx, trachea, main bronchus, bronchioles, respiratory bronchioles, alveolar ducts, to the alveoli for gas exchange. The respiratory system has defensive mechanisms to protect against microbial infections.
Step-by-step explanation:
When a molecule of oxygen is inhaled through the nose, it encounters and travels through several structures on its way to the alveoli of the lungs. The pathway includes the pharynx, the larynx, the trachea, the main bronchus, the bronchioles, the respiratory bronchioles, the alveolar ducts, and finally the alveolar sacs, which contain the alveoli where gas exchange occurs. These structures serve to conduct the inhaled air directly to the alveoli, while also warming, filtering, and humidifying the air.
The sequence of anatomical structures is as follows:
- Pharynx (throat)
- Larynx (voice box)
- Trachea (windpipe)
- Main bronchus
- Bronchioles (smaller air passages)
- Respiratory bronchioles (even smaller air passages)
- Alveolar ducts
- Alveolar sacs
- Alveoli (gas exchange sites)
The respiratory system has several defensive mechanisms to protect against microbial infection, such as mucociliary clearance, immune cells, and reflexes like sneezing and coughing.
Gas exchange between the alveoli and the capillaries occurs through the simple diffusion of oxygen into the blood and carbon dioxide out of the blood, facilitated by the large surface area and thin walls of the alveoli.