Introduction to the Respiratory System (pp. 583–584)

1. Respiration refers not only to ventilation (breathing), but also to the exchange of gases between the atmosphere, the blood, and individual cells. Within cells, the metabolic reactions that release energy are called cellular respiration.

2. In order for the respiratory system to function, the respiratory membranes must be moist, thin-walled, highly vascular, and differentially permeable.

3. The functions of the respiratory system include gaseous exchange, sound production, assistance in abdominal compression, and reflexive coughing and sneezing, and immune response.

Conducting Passages (pp. 585–592)

1. The nose is supported by nasal bones and cartilages.

2. The nasal epithelium warms, moistens, and cleanses the inspired air.

3. Olfactory epithelium is associated with the sense of smell, and the nasal cavity acts as a resonating chamber for the voice.

4. The paranasal sinuses are found in the maxillary, frontal, sphenoid, and ethmoid bones.
   1. These sinuses lighten the skull and are lined with mucus-secreting goblet cells.

   2. Sinusitis is an inflammation of one or more of the paranasal sinuses.

5. The pharynx is a funnel-shaped passageway that connects the oral and nasal cavities with the esophagus and larynx.
   1. The nasopharynx, connected by the auditory tubes to the middle-ear cavities, contains the pharyngeal tonsils, or adenoids.

   2. The oropharynx is the middle portion, extending from the soft palate to the level of the hyoid bone; it contains the palatine and lingual tonsils.

   3. The laryngopharynx extends from the hyoid bone to the larynx and esophagus.

6. The larynx contains a number of cartilages that keep the passageway to the trachea open during breathing and closes the respiratory passageway during swallowing.
   1. The epiglottis is a spoon-shaped structure that aids in closing the laryngeal opening, or glottis, during swallowing.

   2. The vocal folds in the larynx are controlled by intrinsic muscles and are used in sound production.

7. The trachea is a rigid tube, supported by incomplete rings of hyaline cartilage, that leads from the larynx to the bronchial tree.

8. The bronchial tree includes a principal bronchus, which divides to produce lobar bronchi, segmental bronchi, and bronchioles; the conducting division ends with the respiratory bronchioles, which connect to the pulmonary alveoli.

Pulmonary Alveoli, Lungs, and Pleurae (pp. 592–598)

1. Pulmonary alveoli are the functional units of the lungs, where gas exchange occurs; they are small, thin-walled air sacs.

2. The right and left lungs are separated by the mediastinum. Each lung is divided into lobes and lobules.
   1. The right lung is subdivided by two fissures into superior, middle, and inferior lobes.

   2. The left lung is subdivided into a superior lobe and an inferior lobe by a single fissure.

3. The lungs are covered by visceral pleura, and the thoracic cavity is lined by a parietal pleura.
   1. The potential space between these two pleural membranes is called the pleural cavity.

   2. The pleural membranes compartmentalize each lung and exclude the structures located in the mediastinum.

Mechanics of Breathing (pp. 598–603)

1. Quiet (unforced) inspiration is due to contraction of the diaphragm and certain intercostal muscles. Forced inspiration is aided by the scalenes and the pectoralis minor and sternocleidomastoid muscles.

2. Quiet expiration is produced by relaxation of the respiratory muscles and elastic recoil of the lungs and thorax. Forced expiration is aided by certain intercostal muscles and the abdominal muscles.

3. Among the air volumes exchanged in ventilation are tidal, inspiratory reserve, and expiratory reserve volumes.

4. Nonrespiratory air movements are associated with coughing, sneezing, sighing, yawning, laughing, crying, and hiccuping.

Regulation of Breathing (pp. 603–606)

1. Ventilation is directly controlled by the rhythmicity center in the medulla oblongata, which in turn is influenced by the pneumotaxic and apneustic centers in the pons.

2. These brain stem areas are affected by higher brain function and by sensory input from chemoreceptors.

3. Central chemoreceptors are located in the medulla oblongata; peripheral chemoreceptors are located in the aortic and carotid bodies.