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.


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.

READ:   Understanding ARDS

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.

READ:   Anthracosis

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).

READ:   Berylliosis

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.

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...
Pneumonia ICD-9: 486 Description Pneumonia is an acute inflammation of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli of the lung. The inflammation may be either unilateral or bilateral and involve all or a portion of the affected lung. Pneumonia once was the leading cause of death in the United States, but modern antibiotics greatly lessened the incidence of the disease. However, pneumonia still affects close to 4 million people each year and causes death for almost 60,000 individuals yearly in the United States. People ages 65 and older and those with depressed immunity are at greater risk. Pneumonia is often further identified as follows: Lobar pneumonia—Affects one or more lobes of the lung Bronchopneumonia—Also known as lobular pneumonia; bacterial form of the disease Interstitial pneumonia—Characterized by progressive scarring of both lungs Etiology Pneumonia may be caused by microorganisms, such as bacteria, viruses, fungi, protozoa, or rickettsiae. Vira...
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...
Silicosis ICD-9: 502 Description Silicosis, also known as grinder’s disease and potter’s rot, results from the inhalation of crystalline silica dust. Silica is a common mineral found naturally in sand and rock. Silica scars lungs and creates small, discrete nodules in the upper lobes of the lungs. As the disease advances, a dense fibrosis of the lungs develops, and emphysema with respiratory impairment may result. The disease is chronic and progressive. Etiology Silica exposure is common in mines and quarries and in a number of occupations, such as sandblasting, foundry work, ceramics, and glassmaking. The occupations most prone to silica exposure are mining, drilling, blasting, grinding, and abrasive manufacturing. Required exposure varies from 2 to 30 years; the average is 10 years. Signs and Symptoms The disease may be asymptomatic even though x-rays exhibit evidence of nodule formation. Dyspnea on exertion generally is the first symptom. A chronic dry cough that later turns p...
Lung abscess ICD-9: 513.0 Description A lung abscess is an area of necrotized lung tissue containing purulent material. Abscesses are more frequent in the lower dependent portions of the lungs and in the right lung, which has a more vertical bronchus. Etiology Lung abscesses caused by infectious organisms may be a complication of pneumonia. Aspiration of infectious material is the most frequent etiology; however, aspiration due to dysphagia or compromised consciousness (e.g., seizure, cerebrovascular accident, head trauma, alcoholism) appears to be a predisposing factor. Poor oral hygiene, dental infections, and gingivitis are also common indicators. Antibiotic therapy has greatly decreased the number of deaths caused by lung abscess. However, the increased use of corticosteroids, immunosuppressive drugs, and chemotherapeutic agents in the past couple of decades has changed the natural environment of the oropharyngeal cavity and contributed to increased frequency of opportunistic lung abs...