Respiration is essential for life. The body can survive a fair length of time without food, a few days without water, but only minutes without air. Refer to Figure for a review of the structure of the respiratory system.

The respiratory system

FIGURE. The respiratory system.

There are two levels involved in the respiratory process: external and internal respiration. External respiration is the exchange of two gases within the lungs. Oxygen that is present in inhaled air is exchanged for carbon dioxide that diffuses from the blood, across cell walls, into the air spaces of the lungs. The carbon dioxide is then exhaled from the lungs. Internal respiration is the exchange of oxygen and carbon dioxide at the cellular level within the organs of the body. Carbon dioxide is a waste product that results when oxygen and nutrients are metabolized within body cells.

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The respiratory system is divided between the upper respiratory tract and the lower respiratory tract. The upper tract is composed of the organs located outside the chest cavity: the nose and nasal cavities, pharynx, larynx, and upper trachea. The lower tract is composed of the organs located inside the chest cavity: the lower trachea, bronchi, bronchioles, alveoli (microscopic air sacs in the lung), and lungs. Additional parts of the lower tract are the pleural membranes and the respiratory muscles that form the chest cavity.

Midsagittal section of the head and neck

FIGURE. Midsagittal section of the head and neck showing the structures of the upper respiratory tract. (From Scanlon, VC, and Sanders, T: Understanding Human Structure and Function, ed 5. FA Davis, Philadelphia, 2007, p 345, with permission.)

Air enters the nose, which is composed of bone and cartilage and contains ciliated epithelium and cells where the air is humidified and warmed. Tiny hairs just inside the nostrils help prevent particles of dust from entering the nasal cavities. The nasal septum separates the two sides of the nose. The nasal cavities are lined with a membrane that creates mucus designed to further trap bacteria and air pollutants. The upper nasal cavities contain the olfactory receptors that detect odors. Olfactory nerves pass through the ethmoid bone into the brain. The paranasal sinuses, the air cavities in the maxillae, frontal, sphenoid, and ethmoid bones, function to lighten the skull and provide resonance for the voice. These sinuses contain several drainage openings where mucus drains into the nasal cavity.


The pharynx, or throat, is divided into three parts: the nasopharynx, the oropharynx, and the laryngopharynx. The nasopharynx is the passageway for air only. The adenoids are located in the nasopharynx. The soft palate within the nasopharynx prevents food from going up into the nasopharynx. The oropharynx contains the palatine tonsils at the base of the tongue; and the laryngopharynx opens into the larynx and into the esophagus.

The larynx, or voice box, serves as an air passageway and allows for speaking. Cartilage in the larynx prevents the collapse of the larynx, which must stay open for air passage. The epiglottis, located at the top of the larynx, closes over to prevent the entry of food into the larynx. The vocal cords are located on either side of the glottis.

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The trachea contains C-shaped cartilage that keeps the wind pipe open for air passage yet allows food to pass through to the esophagus, which is located behind the trachea. The trachea extends downward into the chest cavity where it splits into the right and left bronchus. These bronchi branch into secondary bronchi leading into the right and left lungs to form the bronchial tree. The branches become smaller, forming bronchioles that terminate in clusters of alveoli, the air sacs of the lungs. The millions of tiny alveoli (only one cell thick) in each lung are important for respiration. They house macrophages to phagocytize any foreign pathogens that might have made it all the way to the lungs. They also permit the diffusion of gases between air in the alveoli and blood in the pulmonary capillaries (also only one cell thick).

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The lungs, located on either side of the heart, are protected by the rib cage and rest on the diaphragm. They are lined with pleural membranes. The parietal pleura lines the chest wall, while the visceral pleura is on the surface of the lung. Pleura serve to prevent friction and keep the two membranes together during breathing. The lungs are soft and cone-shaped and take up most of the thoracic cavity. The lobes of the lung (three on the right and two on the left) contain the bronchial tree.

Anthracosis ICD-9: 505 Description Anthracosis, also called black lung disease or coal worker’s pneumoconiosis, is caused by the accumulation of carbon deposits in the lungs. Simple anthracosis shows small lung opacities. Complicated anthracosis exhibits massive fibrosis in the lungs. Etiology Anthracosis results from inhaling smoke or coal dust. Workers in the coal mining industry are those most likely to develop the disease. Anthracosis frequently occurs with silicosis. Exposure of 15 years or longer is usually required before symptoms develop. Signs and Symptoms Exertional dyspnea, productive cough with inkyblack sputum, and recurrent respiratory infections are common symptoms. Diagnostic Procedures A thorough medical history and physical examination revealing exposure to coal dust are essential and may reveal a barrel chest, rales or crackling sounds in the lungs, a rattling in the throat (rhonchi), and wheezing. Chest x-rays, pulmonary function studies, and arterial bloo...
Atelectasis ICD-9: 518.0 Description Atelectasis is a collapsed or an airless condition of all or part of a lung that allows unoxygenated blood to pass unchanged through the area; this produces hypoxia. The condition may be acute or chronic. Etiology The condition may be caused by obstruction of the lung by foreign matter, mucus plugs, or excessive secretion. It is seen in many clients with COPD or cystic fibrosis and those who smoke heavily. Compression of the lung by tumors, aneurysms, enlarged lymph nodes, or pneumothorax also may cause lung collapse (see Pneumothorax). Atelectasis is sometimes a complication of abdominal surgery or a general consequence of postoperative immobilization. Signs and Symptoms Chronic atelectasis may be marked only by the gradual onset of dyspnea. Acute atelectasis typically includes marked dyspnea, cyanosis, fever, tachycardia, anxiety, and diaphoresis (profuse sweating). There may be a decrease in chest motion on the affected side. Chronic atelecta...
PHARYNGITIS ICD-9: 462 Description Pharyngitis, inflammation of the pharynx, is the most common throat disorder and may be acute or chronic. On the average, children experience sore throats about five times a year, adults twice a year. Etiology Acute pharyngitis can be caused by any of a number of bacterial or viral infections, with viral infections being the most common. Streptococcus pyogenes (causing strep throat) is the most common of many possible bacterial pathogens; influenza virus and common cold viruses are the most common viral pathogens causing the condition. Acute pharyngitis also may arise secondary to systemic viral infections, such as measles or chickenpox. Noninfectious causes of the disease include trauma to the mucosa of the pharynx from heat, sharp objects, or chemical irritants. Chronic pharyngitis is more likely to have a noninfectious origin and is often associated with persistent cough or allergy. Signs and Symptoms The hallmark of acute pharyngitis is sore t...
LEGIONELLA PNEUMONIA (LEGIONNAIRES DISEASE) ICD-9: 482.84 Description A Legionella infection is an acute bronchopneumonia disease. There are two forms of the disease: Legionnaires disease and Pontiac fever. Legionnaires disease is named after an epidemic outbreak of the illness that killed 34 people and sickened more than 200 attending an American Legion convention in Philadelphia in July 1976. The disease may be mild and self-limiting, as in the case of Pontiac fever, or may produce a pneumonia severe enough to be fatal. According to the Centers for Disease Control and Prevention (CDC), between 8000 and 18,000 people are hospitalized with Legionnaires disease each year in the United States. Etiology Legionella infection is caused by the gram-negative bacillus Legionella pneumophila. Other closely related bacteria within the genus Legionella also can produce outbreaks of the disease that are clinically indistinguishable from classic Legionnaires disease. The Legionella bacteria thrive primarily in warm aquatic environm...
ALLERGIC RHINITIS ICD-9: 477.9 Description Rhinitis is inflammation of the nasal membranes. Allergic rhinitis is the most common type of rhinitis. It occurs when there is an allergic reaction to particles in the air. The immune system attacks the particles, causing sneezing and rhinorrhea. Allergic rhinitis is very common, affecting about 20% of the population. The eyes, ears, sinuses, and throat can become inflamed, also. It can be acute or chronic. Etiology The inflammation resulting from rhinitis is triggered by an immunoglobulin E(IgE)–mediated response to an allergen, such as pollen, dust, animal dander, smoke, or mold. When the reaction is caused by pollen, the name hay fever is often used. Pollens that cause a reaction vary among persons and regions. Hot, dry, windy weather with increased amounts of pollen in the air from trees, grasses, and ragweed produce the most symptoms. Allergic rhinitis can coexist with eczema, asthma, and nasal polyps. There is a strong genetic component to alle...