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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