Respiratory System Structure and Gas Exchange (3B) - Bio & Biochem

1. State the law that relates alveolar pressure to surface tension and radius.

   $P=frac{2T}{r}$ (Laplace law). It shows pressure required to prevent collapse is inversely proportional to radius and directly to tension.

2. What type of epithelium lines most of the trachea and primary bronchi?

   Pseudostratified ciliated columnar epithelium with goblet cells. This specialized epithelium traps debris in mucus and uses cilia to propel it out of the airways.

3. What is the direction of $O_2$ diffusion at the alveolus when $P_{A O_2}>P_{a O_2}$?

   $O_2$ diffuses from alveoli into pulmonary capillary blood. Gases diffuse down partial pressure gradients, from higher alveolar to lower blood levels.

4. What is the primary muscle of inspiration in quiet breathing?

   Diaphragm. Its contraction flattens and enlarges the thoracic cavity, reducing pressure for air inflow.

5. What is the Bohr effect in one sentence?

   Increased $CO_2$ or $H^+$ decreases hemoglobin $O_2$ affinity (right shift). It shifts the oxygen-hemoglobin dissociation curve rightward, aiding O2 release in acidic tissues.

6. What is the Haldane effect in one sentence?

   Oxygenation of hemoglobin decreases $CO_2$ carrying capacity, promoting $CO_2$ unloading. It describes how oxygen binding reduces hemoglobin's CO2 affinity, facilitating release in lungs.

7. What is the primary function of cilia and mucus in the conducting airways?

   Mucociliary escalator clears particles and pathogens from airways. Cilia beat to move mucus-trapped debris upward for expulsion, protecting lower airways.

8. What is the major immune cell type that patrols alveoli and removes debris?

   Alveolar macrophages. They phagocytose inhaled particles and microbes to maintain alveolar sterility.

9. Which cartilage structure prevents tracheal collapse during inspiration?

   C-shaped hyaline cartilage rings. These rings provide rigid support to maintain airway patency while allowing esophageal expansion.

10. Which alveolar cell type forms most of the gas-exchange surface?

    Type I pneumocytes (type I alveolar cells). Their thin, squamous structure minimizes diffusion distance for efficient gas exchange.

11. What is the correct anatomical order of airflow from nose to gas-exchange surface?

    Nasal cavity pharynx larynx trachea bronchi bronchioles alveoli. This sequence follows the path of inspired air through the respiratory tract to the site of diffusion.

12. What is the main effect of surfactant on alveoli?

    Decreases surface tension and reduces alveolar collapse. Surfactant lowers surface tension proportionally more in smaller alveoli, stabilizing them per Laplace's law.

13. What is transpulmonary pressure defined as, in terms of lung and pleural pressures?

    $P_{tp}=P_{alv}-P_{ip}$. It represents the pressure gradient that maintains lung expansion against elastic recoil.

14. What is the functional difference between conducting zone and respiratory zone?

    Conducting: air transport; Respiratory: gas exchange (alveoli). Conducting zone conditions and transports air, while respiratory zone enables oxygen and carbon dioxide diffusion.

15. Which alveolar cell type produces pulmonary surfactant?

    Type II pneumocytes (type II alveolar cells). These cells secrete surfactant to lower alveolar surface tension and prevent collapse.

16. What is intrapleural pressure relative to atmospheric pressure under normal conditions?

    Negative relative to atmospheric pressure. This subatmospheric pressure opposes lung recoil, keeping alveoli inflated.

17. What enzyme in red blood cells catalyzes $CO_2+H_2OH_2CO_3$?

    Carbonic anhydrase. It accelerates CO2 hydration to carbonic acid, enabling bicarbonate formation for transport.

18. What is lung compliance, stated as a simple formula relating volume and pressure?

    $C=frac{Delta V}{Delta P}$. It quantifies lung distensibility as volume change per unit pressure change.

19. Identify the primary form in which $CO_2$ is transported in blood.

    Bicarbonate ($HCO_3^-$) in plasma. Most CO2 is converted to bicarbonate for soluble transport, minimizing blood pH changes.

20. What is the name of the airway branch where cartilage disappears and smooth muscle predominates?

    Bronchioles. Absence of cartilage allows smooth muscle to control airway diameter for regulating airflow resistance.

21. What is the relationship between thoracic volume and intrapulmonary pressure (Boyle law)?

    As volume increases, pressure decreases; as volume decreases, pressure increases. Boyle's law dictates inverse relationship between volume and pressure in a closed system at constant temperature.

22. Which variable increases diffusion rate across the alveolar membrane: increased thickness or increased area?

    Increased area increases diffusion rate. Fick's law states diffusion rate is directly proportional to surface area and inversely to membrane thickness.

23. Which muscles are most associated with forced expiration?

    Internal intercostals and abdominal muscles. They contract to decrease thoracic volume, increasing pressure to expel air forcefully.

24. Identify what happens to intrapleural pressure during inspiration.

    It becomes more negative. Thoracic expansion during inspiration further lowers intrapleural pressure to inflate lungs.

25. What is the direction of $CO_2$ diffusion at the alveolus when $P_{a CO_2}>P_{A CO_2}$?

    $CO_2$ diffuses from blood into alveoli. Diffusion follows the partial pressure gradient from higher in blood to lower in alveoli for exhalation.

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