Respiratory system infections
Structure and Function
External respiration, or ventilation, brings oxygen into the lungs
Internal respiration exchanges oxygen and carbon dioxide between blood and body cells
Cellular respiration changes acid produced during metabolism into harmless chemicals in
the cells
Upper respiratory system
Nose, pharynx, mouth, throat associated structures
Purpose: to take in, warm and moisten air
Most common site of infections
Lower respiratory system
Larynx, trachea, bronchi, alveoli in the lungs
Purpose: ventilation, gas exchange
Protective structures of the respiratory system
Mucous membranes
Hairs; ciliated epithelia
Lymphoid tissues (tonsils)
Involuntary responses (coughing)
“Mucociliary escalator” keeps microbes out of
lower respiratory tract
Alveolar macrophages; IgA
Problems of Respiratory System
Common site of infection
Many germs enter nose and mouth
Disorders of the Respiratory System
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1. Pharyngitis, laryngitis, tonsillitis, etc.
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Can be caused by bacteria, viruses or both
Usually self-limiting
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S pyogenes is an important pathogen
Resistant to immune system
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Produces toxins (superantigens)
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Immune reaction (glomerulonephritis, rheumatic fever)
2. Diphtheria disease
also caused by exotoxin
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picked up by some cells but not others
inhibits protein synthesis (kills cells)
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Vaccines have been available for a long time
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neutralize toxin
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Passive immunization is available
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3. Otitis media, Conjunctivitis, Sinusitis
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Both bacterial and viral infectious agents have been found
Lower respiratory infections
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Pneumonia (inflammation of lung)
Tuberculosis (chronic inflammation)
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Whooping cough (kills ciliated cells)
Many infectious agents cause pneumonia
Bacterial
Legionella- spreads in ventilation systems
Mycoplasma (walking pneumonia)
very unusual microbes
“Pneumococcus” (S. pneumoniae)
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Encapsulated; causes inflammation
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Can spread and cause endocarditis, meningitis, septicemia
Tuberculosis
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Gram+ bacterium infects macrophages
Hypersensitivity reaction damages lung tissue
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Many people are infected; most do not develop TB
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Mantoux test detects prior exposure
Aggressive and long-term antibiotic treatment is required
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Several viral pneumonias also described
Adenovirus
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Complications of influenza
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Affects many types of animals (wild and domesticated); source of genetic exchange
Can frustrate immune system due to constant antigen change
kills epithelial cells; spreads rapidly to other cells
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RSV (respiratory syncytial virus)
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Especially dangerous for infants
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Tends to recur
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Kills epithelial cells which can block respiratory passages
Hantavirus pulmonary syndrome
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Spread by inhalation of dust contaminated by mice
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High fatality rate (40%)
No person-to-person spread
Infects capillary epithelium; blood vessel damage and shock
Fungal infections are rare in healthy people
Immune system usually controls growth
Soil source is typical
Can be accidental (after an earthquake, e.g., Coccidioides immitis, “Valley fever”
Histoplasma, a dimorphic fungus
Spread by droppings from birds or bats (do not get sick themselves)
“spelunkers’ disease”
TB-like symptoms
Recovery usually spontaneous, but slow