Chart the course of your journey as you enter the mammalian nasal passages. Indicate all of the structures you pass through on your way to the alveoli. What happens to you when you arrive in the alveoli?

As you embark on your journey through the mammalian respiratory system, starting from the external environment and ending at the alveoli, you traverse several key structures involved in the process of breathing and gas exchange. Here’s a step-by-step chart of your pathway: 1. **External Environment**: The journey begins as you enter the external air through the nose or mouth. 2. **Nasal Cavity**: If entering through the nose, you pass through the nostrils (nares) into the nasal cavity. The nasal cavity is lined with mucous membranes and cilia, which help filter, warm, and humidify the air. 3. **Paranasal Sinuses**: As air moves through the nasal cavity, it can also connect with the paranasal sinuses (frontal, maxillary, ethmoid, and sphenoid) that also help in warming and humidifying the air, as well as reducing the weight of the skull. 4. **Pharynx**: From the nasal cavity, air passes into the pharynx, a muscular tube that serves as a pathway for both air and food. 5. **Larynx**: Next, you enter the larynx (voice box), which contains the vocal cords and plays a crucial role in sound production. The larynx also acts as a gateway to ensure that air passes into the trachea while preventing food from entering the respiratory tract. 6. **Trachea**: Air then moves down the trachea, a tube supported by cartilaginous rings that keeps it open and allows air to flow toward the lungs. 7. **Bronchi**: The trachea divides into two primary bronchi (right and left), each leading to one lung. These bronchi branch further into smaller secondary and tertiary bronchi. 8. **Bronchioles**: The bronchi continue to subdivide into smaller bronchioles, which are the small airways leading directly to the areas of gas exchange in the lungs. 9. **Alveolar Ducts**: As you travel further, the bronchioles open into alveolar ducts. 10. **Alveoli**: Finally, you arrive at the alveoli, tiny air sacs clustered at the ends of the bronchioles. The alveoli are surrounded by capillaries and are the primary site for gas exchange in the lungs. ### What Happens in the Alveoli: Upon arrival at the alveoli: - **Gas Exchange**: Oxygen from the inhaled air diffuses through the thin walls of the alveoli into the surrounding capillaries, where it binds to hemoglobin in red blood cells. At the same time, carbon dioxide, a waste product from cellular metabolism, diffuses from the blood into the alveoli to be exhaled. - **Oxygen Transport**: After oxygen enters the bloodstream, it is transported to cells throughout the body. - **Carbon Dioxide Removal**: The carbon dioxide that has entered the alveoli will eventually be expelled from the body during exhalation, allowing for the continuous cycling of oxygen and carbon dioxide. In summary, the journey through the respiratory tract involves multiple structures that prepare and transport air, culminating in the critical exchange of gases within the alveoli, which is essential for respiration and sustaining life.