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Structural Plan A basic plan of the respiratory system would be similar to an inverted tree if it were hollow; leaves of the tree would be comparable to alveoli, with the microscopic sacs enclosed by networks of capillaries The upper respiratory tract includes the nose, pharynx, and larynx The lower respiratory tract includes the trachea, bronchial tree, and the lungs Pharynx Structure The pharynx (throat) is about 12.5 cm (5 inches) long, and lined by a mucous membrane The two nasal cavities, the mouth, esophagus, larynx, and the auditory tubes all have openings into the pharynx Functions Passageway for food and liquids Air distribution; passageway for air Larynx Structure Several pieces of cartilage form its framework framework It is covered in a mucous lining The vocal cords stretch across the interior of the larynx Functions Air distribution; passageway for air to move to and from lungs Voice production Disorders of the Upper Respiratory Tract Laryngeal cancer Incidence increases with age and alcohol abuse Occurs most often in men over age 50 Treatment may involve removal of the larynx Upper respiratory infection (URI) Rhinitis: nasal inflammation, as in a cold, influenza, or allergy Infectious rhinitis: a common cold Allergic rhinitis: such as in hay fever Pharyngitis (sore throat): inflammation or infection of the pharynx Laryngitis: inflammation of the larynx resulting from infection or irritation Trachea (Windpipe) Structure A mucous-lined tube about 11 cm (4½ inches) long that extends from the larynx into the thoracic cavity C-shaped rings of cartilage hold the trachea open Function Serves as a passageway for air to move to and from the lungs Bronchi, Bronchioles, and Alveoli Structure The trachea branches into right and left bronchi Each bronchus branches into smaller and smaller tubes, eventually leading to bronchioles Bronchioles end in clusters of microscopic alveolar sacs, the walls of which are made up of alveoli Function Bronchi and bronchioles provide a passageway for air to move to and from the alveoli Alveoli allow the exchange of gases between air and blood Lungs and Pleura Structure The lungs are large enough to fill the chest cavity, except for the middle space occupied by the heart and large blood vessels Apex: the narrow upper part of each lung, under collarbone Base: the broad lower part of each lung; rests on the diaphragm Pleura are the moist, smooth, slippery membranes that line the chest cavity and cover the outer surface of the lungs; these reduce friction between the lungs and chest wall during breathing Function: breathing (pulmonary ventilation) Pleurisy: inflammation of the pleura Atelectasis: incomplete expansion or collapse of the lung (alveoli); can be caused by: Pneumothorax: presence of air in the pleural space Hemothorax: presence of blood in the pleural space Respiration Mechanics of breathing Pulmonary ventilation includes two phases called inspiration (movement of air into the lungs) and expiration (movement of air out of the lungs) Changes in size and shape of the thorax cause changes in air pressure within that cavity and in the lungs Air pressure differences actually cause air to move into and out of the lungs Inspiration An active process: air moves into the lungs Inspiratory muscles include the diaphragm and the external intercostals The diaphragm flattens during inspiration, increasing the top-to-bottom length of the thorax The External intercostals contract, elevating the ribs and increasing the size of the thorax from front to back and from side to side The increase in the size of the chest cavity reduces pressure within it, and air enters the lungs Expiration Quiet expiration is a passive process During expiration, the thorax returns to its resting size and shape; elastic recoil of lung tissues aids in expiration Expiratory muscles used in forceful expiration are the internal intercostals and the abdominal muscles The Internal intercostals contract, depressing the rib cage and decreasing the size of the thorax from front to back Contraction of the abdominal muscles elevates the diaphragm, thus decreasing the size of the thoracic cavity from top to bottom Reduction in the size of the thoracic cavity increases its pressure, and air leaves the lungs Disorders of the Lower Respiratory Tract Lower respiratory infection Acute bronchitis or tracheobronchitis: inflammation of the bronchi or bronchi and trachea caused by infection (usually resulting from the spread of a URI) Pneumonia: acute inflammation (infection) in which lung airways become blocked with thick exudates Tuberculosis (TB): a chronic, highly contagious lung infection; can progress to involve tissues outside the lungs and pleurae Lung cancer: a malignant tumor of the lungs; occasionally treatable Disorders of the Lower Respiratory Tract Obstructive pulmonary disorders Obstruct breathing Chronic obstructive pulmonary disease (COPD) can develop from preexisting obstructive conditions Chronic bronchitis involves chronic inflammation of the bronchial tree Emphysema involves a reduced surface area of lungs caused by rupture or other damage to the alveoli Asthma involves recurring spasms of the airways accompanied by edema and mucus production