CHAPTER TWENTY-FIVE
Content Review
1. Mucus covers the respiratory epithelium, where it acts as a lubricant and prevents
dehydration. The layer of sticky mucus also traps foreign particles and humidifies the
inhaled air. If we are exposed to airborne allergens, large quantities of small
particulate material, irritating gases, or pathogens, the rate of mucin production
increases.
2. Nonkeratinized stratified squamous epithelium lines the oropharynx because this
epithelium is strong enough to withstand the abrasion of swallowed food.
3. Increasing the tension on the vocal folds increases the pitch of the sound produced.
Conversely, the less tense the vocal folds, the less the vocal folds vibrate and the
lower the pitch of the sound. The loudness of the sound depends on the force of the
air passing across the surface of the vocal folds. A large volume of air forced past the
vocal folds produces a loud sound.
4. The bronchial tree structures, from largest to smallest, are primary bronchi, secondary
bronchi, tertiary bronchi, smaller bronchi, bronchioles, and terminal bronchioles.
5. The bronchioles have such a small diameter that they do not need wall support from
cartilage since they will not collapse during inhalation.
6. Septal cells secrete pulmonary surfactant onto the alveolar surface. This material
helps reduce surface tension to prevent the collapse of the small air sacs.
7. The left lung is slightly smaller than the right lung. Its medial surface indentation,
called the cardiac impression, accommodates the heart. The right lung has three lobes
(superior, middle, and inferior), while the left lung has only two (superior and
inferior).
8. In general, the thoracic cavity becomes larger when you inhale and smaller when you
exhale. Vertical dimensional changes occur with movements of the diaphragm. The
diaphragm contracts during inhalation, and relaxes and is brought back to its original
position during exhalation. Lateral dimensional changes occur during inhalation when
the ribs are elevated. The external intercostals elevate the ribs in general, while the
scalenes elevate the first and second ribs specifically during inhalation. During
normal exhalation, the ribs are brought back to original position merely by relaxation
of the external intercostals and scalenes. However, the internal intercostals depress
the ribs during forced exhalation. Finally, a slight anterior-posterior dimensional
change to the thoracic cavity occurs due to anterior movement of the inferior portion
of the sternum during inhalation. During exhalation, the inferior portion of the
sternum moves posteriorly and returns to its original position.
9. The autonomic nervous system respiratory centers in the pons are the apneustic center
and the pneumotaxic center. Both areas influence the ventilation rate by modifying
the activity of the respiratory center in the medulla oblongata.
10. The dorsal respiratory group (DRG) is the inspiratory center. The ventral respiratory
group (VRG) is the expiratory center. Both comprise the respiratory center. The DRG
controls the motor neurons that stimulate the muscles of inspiration, and is activated
during both normal inhalation and forced, active inhalation. In contrast, the VRG
functions only during forced exhalation. During normal quiet breathing, the VRG is
inactive, and exhalation is a passive event that does not require nervous stimulation.