D’YOUVILLE COLLEGE
BIOLOGY 307/607 - PATHOPHYSIOLOGY
Lecture 13 - RESPIRATORY DISORDERS
Chapter 12
1.
Anatomy of Respiratory System:
• lungs & pleural cavities: each lung supplied by a primary bronchus
- secondary bronchi supply lobes (three in right, two in left) (fig. 12 - 1 &
ppt. 1)
- lungs are housed in pleural cavities, normally containing thin film of
pleural fluid (fig. 12 - 2 & ppt. 2), which is below atmospheric pressure
- lung collapse, due to elastic interstitial tissue in lungs + strong internal
surface tension, is prevented by pleural fluid
- lung surface tension is alleviated by pulmonary surfactant
- disruption of pleural fluid film, e.g. pneumothorax, may cause collapsed
lung (fig. 12 - 32 & ppt. 3); also hydrothorax & hemothorax
• airways of upper & lower respiratory tract: upper respiratory tract: airways
of nasal cavities, pharynx, larynx, & cervical portion of trachea (fig. 12 - 4 & ppt. 4)
- lower respiratory tract: lower trachea & bronchial tree (intrathoracic)
- bones adjacent to nasal cavities (maxillae, frontal, ethmoid, & sphenoid)
contain air spaces (paranasal sinuses) that are lined with mucous membranes and
drain into nasal cavities (fig. 12 - 3 & ppt. 5)
- larynx provides opening (glottis) from pharynx to trachea (& bronchial
tree); it is composed of a cartilaginous skeleton & contains vocal folds that facilitate
phonation (ppt. 6)
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- trachea & bronchial tree (fig. 12 - 5 & ppt. 7) are prevented from collapse
by reinforcing cartilages (C-shaped in trachea, coiled in primary, secondary &
smaller bronchi) (ppt. 8)
- directly posterior to great vessels of heart, trachea bifurcates into two
primary bronchi (right is more vertical than left, which makes it more vulnerable to
admitting aspirated material)
- at the point of bifurcation, an internal ridge (carina) triggers violent
cough reflex when contacted by aspirated material
- bronchioles are the microscopic passageways extending from smallest
bronchi; lined with smooth muscle, but no cartilages; smallest conducting
bronchioles (terminal bronchioles) extend to respiratory bronchioles
- respiratory units include respiratory bronchioles, alveolar ducts, & alveoli
-- all composed of thin respiratory membranes facilitating gas exchange with blood
capillaries (fig. 12 - 6 & ppt. 9)
2.
Physiology of Respiratory System:
• ventilation: movement of air into & out of lungs, achieved by bellows action
of diaphragm assisted by intercostal muscles
- several volumes (measured by pulmonary function tests -- table 12 - 1):
- total lung capacity = vital capacity + residual volume; vital capacity =
tidal volume + inspiratory reserve volume + expiratory reserve volume) (fig. 12 - 12
& ppt. 10); FEV1 (= one second forced expiratory volume) is useful in diagnosis of
COPD
• gas exchange: oxygen uptake from alveolar air to blood (hemoglobin
oxygenation) and carbon dioxide discharge from blood to alveolar air depend on
maintenance of adequate diffusion gradients, maintained by ventilation to
perfusion ratio (fig. 12 - 11 & ppt. 11)
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- in lungs, oxygenation of hemoglobin provides a chemical impetus for
conversion of bicarbonate ion (main form of CO2 transport) to carbonic acid; this is
converted to CO2 and H2O (by enzyme carbonic anhydrase in red cells) (fig. 12 - 7 &
ppt. 12); reverse reactions occur in tissues (fig. 12 - 8 & ppt. 13)
- defenses: mucous blanket (contains antibacterial and antiviral agents) on
ciliated epithelium (fig. 12 - 4 & ppt. 14) & macrophages in respiratory units facilitate
removal of respiratory contaminants (figs. 12 - 9, 12 - 10 & ppts. 15 & 16)
4.
Respiratory Diseases:
• signs & symptoms: cough, a reflex commonly associated with respiratory
disorders, helps to clear excessive mucus &/or foreign matter; sputum from
productive cough may have diagnostic significance
- dyspnea or shortness of breath may indicate presence of airway obstruction
or increased stiffness (reduced compliance) of lung
- cyanosis is a bluish tone to skin, indicating larger than normal amounts of
reduced hemoglobin in peripheral circulation (poor oxygenation)
• disruption of ventilation to perfusion ratio (V/Q) is usual impairment with
respiratory diseases (fig. 12 - 10 & ppt. 17)
- perfusion may be reduced (hypoperfusion) by left heart failure or
thromboembolism (fig. 12 - 13); pulmonary hypertension results & induces increased
resistance to blood flow; right failure (cor pulmonale) reduces cardiac output to
pulmonary circulation
- ventilation may be reduced (hypoventilation) by chronic airway
obstruction (obstructive pulmonary diseases) or by failure of lungs to expand
adequately (restrictive pulmonary diseases)
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• chronic obstructive pulmonary diseases (COPD): usually a result of
overproduction of mucus; in upper respiratory infections (colds, laryngitis,
bronchitis), disorders are normally resolved by cough and defensive responses
(immunity, phagocytosis); however, if mucus is not cleared, more serious chronic
conditions may become established, e.g., chronic bronchitis, emphysema
- chronic bronchitis is characterized by unresolved irritation of respiratory
mucosa (most often a consequence of smoking), persistent productive cough,
dyspnea, and increased incidence of infections (figs. 12 - 14, 12 - 15 & ppts. 18 & 19)
- emphysema: widespread destruction of partitions between alveoli,
resulting in loss of respiratory membrane & reduced gas exchange (figs. 12 - 16, 12 17)
- phagocytes attracted to sites of irritant damage secrete elastase; this causes
destruction of interstitial elastic tissue & results in airway collapse (fig. 12 - 18 & ppt.
20)
- in some smokers, there is a decline of a plasma protein that normally inhibits
elastase (from macrophages); elastic tissue damage progresses unopposed (fig. 12 - 19
& ppt. 21)
- damage may be confined to respiratory bronchioles (centrilobular) or may
extend to more distal parts of respiratory units (panlobular) (fig. 12 - 20 & ppt. 22)
- asthma: although less frequent than chronic bronchitis or emphysema,
asthma is included in the trio of conditions constituting COPD
- hypersecretion of mucus, bronchoconstriction, and bronchial swelling
produce obstruction of airway
- condition is reversible and may dissipate for some time but return later
- IgE mediated - type I hypersensitivity is a major cause; irregularities of
autonomic nervous system receptors or drug sensitivities may also be to blame (fig.
12 - 22 & ppt. 23)
- cystic fibrosis: genetic condition resulting in overproduction of thick mucus
in many glands, including lungs; sometimes included in COPD
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• restrictive lung disease: reduced expansion capability of lungs that may
result from external conditions (extrinsic restrictions) or changes in lung interstitial
tissue (intrinsic restrictions)
- extrinsic restrictions (fig. 12 - 23 & ppt. 24):
- abnormalities of thoracic cage morphology (due to trauma or
congenital malformation, e.g., kyphoscoliosis)
- muscular weakness due to muscular dystrophies
- neural abnormalities due to botulism, poliomyelitis, amyotrophic
lateral sclerosis, or myasthenia gravis
- excessive adipose interference (obesity)
- intrinsic restrictions: mainly involves capillary damage with accompanying
interstitial damage that reduces lung compliance; main conditions are acute (adult
respiratory distress syndrome - ARDS) or chronic (chronic intrinsic restrictive lung
disease - CIRLD)
- ARDS: main etiologic factor is pulmonary edema that results in lung
stiffness & interferes with respiratory exchange; capillary damage from pulmonary
congestion or hypertension (figs. 12 - 24, 12 - 25 & ppts. 25 & 26), or from other
damaging events (fig. 12 - 26 & ppt. 27) such as infections (pneumonias), circulatory
shock & blood-borne toxins
- CIRLD: chronic inflammation of interstitial tissue reduces lung
compliance; prolonged exposure to certain irritants (pneumoconioses - fig. 12 - 27 & ppt.
28), infections (especially viral), or immune conditions (autoimmunity,
hypersensitivity) are the three main etiologic factors (table 12 - 5)
• lung infections: bacterial pneumonias (rarer, due to success of antibiotics)
feature alveolus-centered inflammations, resulting in solid mass of macrophages
(consolidation)
- viral pneumonias feature inflammations of interstitial tissues
- also protozoan (Pneumocystis) type pneumonia; mostly associated with
compromised immune response, e.g. as in AIDS
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• lung cancer - central or peripheral tumors produce varying and progressive
levels of destruction (fig. 12 - 34 & ppt. 29)
• respiratory failure: deficient oxygen level (hypoxia, hypoxemia) sometimes
accompanied by elevated carbon dioxide level (hypercapnia) (fig. 12 - 29)