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.

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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).


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.

Chronic obstructive pulmonary disease: pulmonary emphysema and chronic bronchitis ICD-9: 491.21 Description Chronic obstructive pulmonary disease (COPD) is a functional diagnosis given to any pathological process that decreases the ability of the lungs and bronchi to perform their function of ventilation. It is an umbrella term that includes pulmonary emphysema and chronic bronchitis. COPD affects 12 million Americans, and it is estimated that 12 million more are undiagnosed. It is a common cause of death and disability in the United States. Pulmonary emphysema (ICD-9:492) is the permanent enlargement of the air spaces beyond the terminal bronchioles resulting from destruction of alveolar walls. As a consequence of this destruction, the lungs slowly lose their normal elasticity. Air reaches the alveoli in the lungs during inhalation but may not be able to escape during exhalation. Evidence suggests that some forms of the emphysema may be hereditary. In rare instances, emphysema is associated with a deficiency of a1-antitrypsin, a protein that plays a role in ...
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...
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...
Cor pulmonale ICD-9: 416.9 Description Cor pulmonale is hypertrophy and failure of the right ventricle of the heart. Lung disease may cause pulmonary hypertension. As a result, the workload of the heart is increased, and the right ventricle hypertrophies in an effort to force blood into the lungs. Eventually the right ventricle is weakened by this effort, and blood pools in the right ventricle. Etiology Cor pulmonale is caused by various disorders of the lungs, the pulmonary vessels, or the chest wall that impede pulmonary circulation. Disorders that may lead to cor pulmonale include COPD, bronchiectasis, pneumoconiosis, pulmonary hypertension, kyphoscoliosis (abnormal backward and lateral curvature of the spine), multiple pulmonary emboli, upper airway obstruction, and living at high altitudes. The condition may be acute but is more commonly chronic. Signs and Symptoms Signs and symptoms include a productive, chronic cough; exertional dyspnea; fatigability; and wheezing respirations...
Pulmonary embolism ICD-9: 416.2 Description A pulmonary embolism is a mass of undissolved matter in the pulmonary artery or one of its branches. It is the most common pulmonary complication among hospitalized individuals with about 250,000 incident cases occurring annually. It is not considered a disease itself but is a complication of venous thrombosis. It is potentially lethal. Etiology FIGURE. Embolism. (From Thomas, CL : Taber’s Cyclopedic Medical Dictionary, ed 21. FA Davis, Philadelphia, 2005, p 744, with permission.) A pulmonary embolism generally originates in the pelvic veins or deep lower extremity veins and travels through the circulatory system until it blocks a pulmonary artery. At high risk for pulmonary emboli are individuals immobilized with chronic diseases, those in body casts, persons with congestive heart failure or neoplasms, and postoperative clients. Also at risk are pregnant women; women taking oral contraceptives; and individuals with venous diseases, such as var...