EMT-I_Ch05_114-239 9/25/04 1:34 PM Page 201 Chapter 5 The Human Body 201 The Respiratory System Pharyngeal tonsil The respiratory system is associated with breathing, Palatoglossal gas exchange, and the entrance of air into the body. The arch organs and structures in the respiratory system are Uvula divided into the upper and lower airways. The upper airway includes the mouth, nasal cavity, and oral cav- Palatine tonsil ity, and the lower airway includes the larynx, trachea, Palatopharyngeal bronchi, bronchioles, and alveoli. arch Lingual tonsil The Upper Airway Figure 5-111 The tonsils. A human can breathe air into the body through either the nose, also called the nasal cavity or nasopharynx, or through the mouth, also called the oral cavity or quite large in the infant and decreases in size with oropharynx. The nasopharynx and oropharynx connect age. Often, there is no discernible thymic tissue in posteriorly to form a cavity called the pharynx older adults. The thymus produces lymphocytes, which Figure 5-112 ᮢ . move to other lymph tissues to help fight infection. The nasopharynx extends from the internal nares to The thymus plays a major role in immunity, especially the uvula (a small fleshy mass that hangs from the soft in early life. palate). The oropharynx extends from the uvula to the A Artery Vein Alveolus Nasal cavity Bronchiole Mouth (oral cavity) Pharynx Larynx Capillary network Trachea Left bronchus Right bronchus B Alveoli Terminal bronchiole Capillaries Figure 5-112 The respiratory system. A. The upper and lower airway divisions of the respiratory system. The insert shows a higher magnification of the alveoli, where oxygen and carbon dioxide exchange occurs. B. A scanning electron micrograph of the alveoli, showing the rich capillary network surrounding them. © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2120 EMT-I_Ch05_114-239 9/25/04 1:34 PM Page 202 202 Section 1 Preparing to be an EMT-I epiglottis, the thin plate of cartilage that closes over the glottic opening during swallowing. Inferiorly, the phar- A ynx leads to the separate openings of the respiratory Epiglottis system (larynx) and the digestive system (esophagus). The external openings of the nasopharynx are the external nares or nostrils. The interior nares comprise the posterior opening from the nasopharynx into the Vestibular fold pharynx. The nasal septum separates the nasopharynx Thyroid cartilage (false vocal cord) into two parts. The floor of the nasal cavity is the hard True vocal cord palate. The lateral walls of the nasopharynx contain three bony ridges, the conchae. Together, the conchae form a set of bony convolutions, called the turbinates, Tracheal which help to maintain laminar (smooth) airflow. Below cartilages each turbinate is a passageway called a meatus. Each meatus contains the drainage opening from the sinus and the nasolacrimal ducts (the ducts that drain tears from the lacrimal sac). B The Lower Airway The beginning of the lower airway, the larynx, consists of several sections of cartilage held together by liga- ments Figure 5-113 ᮣ . The larynx includes two pairs of ligaments that form the vocal cords. The superior portion of the vocal cords forms the vestibular folds, or false vocal cords; the inferior portion forms the true vocal cords. Vibration of the true vocal cords results in production of sounds and speech. The true vocal cords plus the opening between them is called the glottis. Vocal cords The trachea is immediately inferior to the larynx and is approximately 4Љ long in most adults. The tra- Figure 5-113 The larynx. A. Longitudinal section of the larynx showing the location of the vocal cords. Note the presence of chea is a tube made up of cartilage and other connec- the false vocal cord. B. View into the larynx showing the true tive tissue and conveys air to and from the lungs. The vocal cords from above. cartilage forms the anterior and lateral sides of the tra- chea, providing both protection and an open passage- way for air. The esophagus is immediately posterior to of the bronchiole. Each respiratory bronchiole divides the cartilage-free posterior wall of the trachea. At the to form alveolar ducts. Each alveolar duct ends in clus- level of the fifth thoracic vertebra, the trachea branches ters known as alveoli, tiny sacs of lung tissue in which into the right and left mainstem bronchi at the carina, gas exchange takes place. The lung contains approxi- a projection of the lowest portion of the tracheal carti- mately 300 million alveoli; each alveolus is about 0.33 lage Figure 5-114 ᮣ . mm in diameter. Capillaries cover the alveoli. The alve- Beyond the carina, air enters the lungs through the olocapillary membrane lies between the alveolus and mainstem bronchi. The point of entry for the bronchi, the capillary and is very thin, consisting of only one vessels, and nerves into each lung is called the hilum. cell layer. Respiratory exchange between the lung and The mainstem bronchi divide into the secondary blood vessels occurs in the alveoli at the alveolocapil- bronchi, each one going to a separate lobe of the lung lary membrane. (see Figure 5-114). The lungs are the primary organs of breathing. The Secondary bronchi branch into tertiary bronchi, right lung contains three lobes (the upper, middle, and which continue to branch several times. After several lower lobes); the left lung contains only two (the upper generations of successive branching, bronchioles, very and lower lobes). In the left lung, a portion known as small subdivisions of the bronchi, are formed. Respi- the lingula forms the equivalent of the middle lobe in ratory bronchioles develop from the final branching the right lung. The lungs are surrounded by a mem- © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2120 EMT-I_Ch05_114-239 9/25/04 1:35 PM Page 203 Chapter 5 The Human Body 203 Trachea (windpipe) Alveoli Primary bronchi Secondary bronchi Figure 5-114 The mainstem bronchi. The upper insert shows the bifurcation of the trachea at the carina into the right and left mainstem bronchi. brane of connective tissue known as pleura. Another pleural membrane lines the inner borders of the rib cage, or pleural cavity. The pleural membrane that covers the lungs is referred to as the visceral pleura, and the pleural membrane that lines the pleural cavity is the parietal pleura. A potential space known as the pleural space exists between the visceral and parietal pleura. Nor- mally, the two membranes are close together and a space does not exist. Both layers of pleura work together to help maintain normal expansion and contraction of the lung. Under certain disease conditions or following trauma, fluid and/or air may accumulate in the pleural space, resulting in hemothorax (a collection of blood in the pleural space) or hemopneumothorax (a collec- tion of blood and air in the pleural space), potentially causing respiratory problems Figure 5-115 ᮣ . The lungs receive blood in two ways. Deoxygenated blood flows from the right ventricle via the pulmonary Figure 5-115 The pleural membranes. Normally, there is no arteries. This blood flows through pulmonary capil- space between the pleural membranes. When air, blood, or both laries, is reoxygenated at the alveoli, and then returns enter the potential space, a potentially life-threatening condition can develop. to the heart via the pulmonary veins. © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2120 EMT-I_Ch05_114-239 9/25/04 1:35 PM Page 204 204 Section 1 Preparing to be an EMT-I Acute asthma is a recurring condition of reversible acute airflow obstruction in the lower airway. About 8.9 million people in the United States have asthma, and thousands with asthma die each year. It is the most common chronic disease of childhood. Four distinct events occur in an asthma attack. Smooth muscle spasm occurs when the muscle layers around the airways constrict (bronchospasm), resulting in narrowing of the airway diameter. Increased secre- tion of mucus causes mucus plugging, further decreasing the airway diameter, and finally, inflammatory cell prolif- eration occurs. White blood cells accumulate in the airway and secrete substances that worsen the muscle spasm and increase mucus production. The most common cause of an asthma attack is an upper respiratory infection, such as bronchitis or a cold. Other causes include changes in environmental conditions; emotions, especially stress; allergic reactions to pollens, foods (chocolate, shellfish, milk, nuts) or drugs (penicillin, local anesthetics); and occupational exposures. The severity of asthma attacks varies among patients. In very severe cases (status asthmaticus), the patient may die as a result of respiratory failure. In other cases, treatment may produce rapid improvement and resolution of the asthmatic crisis. The patient’s level of compliance and degree of ambulatory control may be a strong mitigating fac- tor in the development of complications. Patients with potentially fatal asthma have a greater likelihood of a shorter duration of premonitory symptoms, worse lung function, and medication noncompliance. Understanding the underlying pathophysiology has radically impacted chronic drug therapy of asthma. Inhaled corticosteroids are now considered a mainstay of preventive therapy primarily for their anti-inflammatory effect. Oral and IV steroids have been used for the same purpose in acute attacks for many years. In addition, drugs are con- stantly being developed that block other inflammatory compounds involved in an acute attack. One newly available drug, zileuton, inhibits 5-lipoxygenase, an enzyme that catalyzes formation of leukotrienes, known inflammatory medi- ators in asthma. Another drug, zafirlukast, directly inhibits the actions of leukotrienes. Both drugs are approved by the FDA in the chronic treatment of asthma. The most promising combination of drugs for chronic therapy is an inhaled long-acting beta2 agonist combined with an inhaled steroid.