RESPIRATORY TRACT
LUNGS
Congenital Anomalies
Developmental defects of the lung include the following:
-Agenesis or hypoplasia of lungs, one lung, or single lobes
- Tracheal and bronchial anomalies (atresia, stenosis, tracheoesophageal
fistula)
- Vascular anomalies
- Congenital lobar overinflation (emphysema)
-Foregut cysts
- Congenital pulmonary airway malformation
Pulmonary hypoplasia. Is the defective development of both lungs
resulting in: Decreased weight, volume, of lung compared to the body
weight and gestational age.
Foregut cysts represent an abnormal detachment of primitive foregut and
are most often located in the hilum of middle mediastinum.
Pulmonary sequestration refers to the presence of a discrete mass of the
lung tissue without any normal connection to the airway system.
Atelactasis (collapse):
It refers either to incomplete expansion of the lungs (neonatal atelactasis) or
to the collapse of previously inflated lung, producing areas of relatively
airless pulmonary parenchyma.
Acquired ate.:
Encountered mainly in adults, devided into resorption (or obstruction),
compression, and contraction ate..
♦RESORPTION ATE.:Is the consequences of complete obstruction of an airway, which leads to
resorption of the oxygen trapped in the dependent alveoli, since lung volume
is diminished, the mediastinum shifts toward the atelactatic lung.
♦COMPRESSION ATE.:Results whenever the pleural cavity is partially or completely filled by fluid
exudates, tumor, blood, or air, when air pressure impinges on and threatens
the function of the lung and mediastinum.
♦CONTRACTION ATELACTASIS:Occurs when local or generalized fibrotic changes in the lung or pleura
prevent full expansion.
♦ significant atelactasis reduces oxygenation and predispose to infection.
♦ it is a reversible disorder (except that caused by contraction).
OBSTRUCTIVE VERSUS RESTRICTIVE PULMONARY
DISEASES
Depending on the pulmonary function test pulmonary diseases can be
classified into two categories:
1- Obstructive diseases (OPD), characterized by an increase in resistance to
airflow owning to partial or complete obstruction at any level of respiratory
tract.
2- restrictive diseases (RPD), reduce expansion of the lung parenchyma, with
reduce total lung capacity.
Obstructive diseases (OPD):- emphysema.
- Chronic bronchitis.
- Asthma.
- And broncheactasis.
EMPHYSEMA
It is a condition of the lung characterized by abnormal permanent enlargement
of the airspaces distal to the terminal bronchioles, accompanied by destruction
of their walls and without obvious fibrosis.
♦ overinflation: enlargement of the airspaces unaccompanied by destruction.
TYPES:
According to the anatomic distribution in the lobule:
- centriacinar.
- Panacinar.
- Paraseptal.
- Irregular.
1- CENTRIACINAR EMPHYSEMA:
- involve the central or proximal parts of the acini (formed by the respiratory
bronchioles ), sparing the distal part.
- More common in the upper lobes.
- The wall often contain large amount of black pigment.
- It occurs predominantly in heavy smokers , often in association with chronic
bronchitis.
2- PANACINAR E.:- the acini are uniformly enlarged from the level of the respiratory bronchiole
to the terminal blind alveoli.
- More commonly in the lower zone of the lung, and most severe in the bases.
- Associated with alpha1 antitrypsin deficiency.
3- DISTAL ACINAR E.:- The distal part is predominantly involved.
- Occur adjacent to the areas of fibrosis, scarring, or atelactasis.
- Usually more severe in the upper part of the lung.
4- Airspaces enlargement with fibrosis (irregular emphysema),
- acinus irregularly involved.
- Almost invariably associated with scarring.
- Usually asymptomatic and insignificant.
PATHOGENESIS:
For the destruction of the alveolar walls the most plausible hypothesis is the
◘ protease antiprotease mechanism aided by ◘ oxidant-antioxidant imbalance.
Alveolar wall destruction result from an imbalance between protease (mainly
elastase) and antiprotease in the lung.this theory based on important
observations; the homozygous patients with a deficiency of protease inhibitor
(α1-AT) have markedly enhanced tendency to develop pulmonary emphysema.
This theory also explains the deleterious effect of cig. Smoking both increased
elastase availability and decreased antielastase activity occur in smokers.
Smoking also cause oxidant- antioxidant imbalance, tobacco smoke contain
abndant amount of free radicals (reactive oxygen species which deplete
antioxidant mechanisms in the lung, thereby inciting tissue damage.
Figure 15-7 Pathogenesis of emphysema. The protease-antiprotease imbalance and oxidantantioxidant imbalance are additive in their effects and contribute to tissue damage. 1 antitrypsin (1 -AT) deficiency can be either congenital or "functional" as a result of oxidative
inactivation. See text for details. IL-8, interleukin 8; LTB4 , leukotriene B4 ; TNF, tumor
necrosis factor.
MORPHOLOGY:
GROSS: voluminous lungs, large blebs or bullae may bee seen.
MIC:
there are abnormally large alveoli separated by thin septa, there are
even larger abnormal airspaces.often the respiratory bronchioles and vasculature
of the lung deformed and compressed.
Figure 15-6 A, Centriacinar emphysema. Central areas show marked emphysematous damage (E),
surrounded by relatively spared alveolar spaces. B, Panacinar emphysema involving the
entire pulmonary architecture.
CHRONIC BRONCHITIS
Chronic bronchitis, so common--among habitual smokers and inhabitants of
smog-laden cities. When persistent for years, it may (1) progress to chronic
obstructive airway disease, (2) lead to cor pulmonale and heart failure, or (3)
cause atypical metaplasia and dysplasia of the respiratory epithelium,
providing a rich soil for cancerous transformation. Important definitions in
bronchitis include the following:
Chronic bronchitis per se is defined clinically. It is present in any patient
who has persistent cough with sputum production for at least 3 months in at
least 2 consecutive years, in the absence of any other identifiable cause.
* In simple chronic bronchitis, patients have a productive cough but no
physiologic evidence of airflow obstruction.
* Some individuals may demonstrate hyperreactive airways with intermittent
bronchospasm and wheezing. This condition is called chronic asthmatic
bronchitis.
- Finally, some patients, especially heavy smokers, develop chronic airflow
obstruction, usually with evidence of associated emphysema, and are
classified as showing obstructive chronic bronchitis.
Pathogenesis. The primary or initiating factor in the genesis of chronic
bronchitis appears to be chronic irritation by inhaled substances such as
tobacco smoke (90% of patients are smokers) and grain, cotton, and silica
dust. Bacterial and viral infections are important in triggering acute
exacerbation of the disease. Both sexes and all ages may be affected, but
chronic bronchitis is most frequent in middle-aged men. Chronic bronchitis
is 4 to 10 times more common in heavy smokers regardless of age, sex,
occupation, and place of dwelling.
The earliest feature of chronic bronchitis is hypersecretion of mucus in the
large airways, associated with hypertrophy of the submucosal glands in the
trachea and bronchi.2° Proteases released from neutrophils, such as
neutrophil elastase and cathepsin, and matrix metalloproteinases, stimulate
this mucus hypersecretion. As chronic bronchitis persists, there is also a
marked increase in goblet cells of small airways—small bronchi and
bronchioles—leading to excessive mucus production that contributes to
airway obstruction. It is thought that both the submucosal gland
hypertrophy and the increase in goblet cells are a protective metaplastic
reaction against tobacco smoke or other pollutants. Many of the respiratory
epithelial effects of environmental irritants are believed to be mediated
through the epidermal growth factor (EGF) receptor.
Morphology. Grossly, there may be hyperemia. swelling, and edema of the
mucous membranes, frequently accompanied by excessive mucinous
mucopurulent secretions layering the epithelial surfaces. Sometimes, heavy
casts of secretions and pus fill the bronchi and bronchioles.
The characteristic histologic features of chronic bronchitis are:
◘ chronic inflammation of the airways (predominantly lymphocytes)
◘ and enlargement of the mucus-secreting glands of the trachea and bronchi.
◘Although the numbers of goblet cells increase slightly, the major increase
is in the size of the mucous glands.
◘The bronchial epithelium may show squamous metaplasia and dysplasia.
◘There is marker narrowing of bronchioles caused by goblet cell metaplasia,
mucus plugging, inflammation, and fibrosis.
◘ In the most severe cases, there may be obliteration of lumen due to fibrosis
(bronchiolitis obliterans).
Clinical Features. The cardinal symptom of chronic bronchitis is a
persistent cough productive of sputum. For years, no other respiratory
functional impairment is present but eventually, dyspnea on exertion
develops. With time, and usually with continued smoking, other elements of
COPD may appear, including hypercapnia, hypoxernia, and mild cyanosis.
ASTHMA
it is a chronic inflammatory disorder of the airways that causes recurrent
episodes of wheezing, breathlessness, chest tightness, and cough especially
at night or in the early morning.
TYPES:
1- atopic; most common type, usu begins at childhood, triggered by
environmental antigens, e.g.dust, pollens, animal danders, and foods. A
positive family history of atopy is common, asthmatic attacks are often
preceded by allergic rhinitis, urticaria, or eczema.
2- Nonatopic asthma: most commonly triggered by RTI especially viral, a
positive family history is uncommon.serum IgE level is normal, there is no
other associated allergies, pathogenesis; due to hyperirritability of the
bronchial tree; virus induce inflammation of the respiratory mucosa lowers
the threshold of the subepithelial vagal receptors to irritants.
3- Drug-Induced asthma: Aspirin- sensitive asthma.
4- Occupational asthma: simulated by fumes, organic, gases, and chemical
dusts.
Morphology;
1- whorls of epith (Curshman spirals).
2- Thickening of the b.m. of the bronchial epith.
3- Edema, and infl. Infil.
4- Increase in the size of the submucosal glands.
5- Hypertrophy of s.m. of bronchial wall.
Bronchiectasis
It is a disease characterized by permanent dilation of bronchi and
bronchioles caused by destruction of the muscle and elastic tissue,
resulting from or associated with chronic necrotizing infections. To be
considered bronchiectasis, dilation should be permanent; reversible
bronchial dilaion often accompanies viral and bacterial pneumonia.
because of better control of lung infections, bronchiectasis is now an
uncommon condition. It is manifested clinically by high fever, and
expectoration of copious amounts of fouling, purulent sputum.
Bronchiectasis develops in association with a variety of conditions, which
include the following:
• Postinfectious conditions, including necrotizing pneumonia caused by
bacteria (Mycobacterium tuberculosis, Staphylococcus aureus,
Haemophilus influenzae, Pseudomonas), viruses (adenovirus, influenza
virus, HIV), and fungi (Aspergillus species)
• Bronchial obstruction, owing to tumor, foreign bodies, and occasionally
mucus impaction, in which the bronchiectasis is localized to the obstructed
lung segment
• Other conditions, including rheumatoid arthritis, systemic lupus
erythematosus, inflammatory bowel disease, and post-transplantation
(chronic lung rejection, and chronic graft-versus-host disease after bone
marrow transplantation)
Etiology and Pathogenesis. Obstruction and infection are the major
influences associated with bronchiectasis, and it is likely that both are
necessary for the development of full-fledged lesions, although either may
come first. After bronchial obstruction (e.g., by mucus impaction, tumors,
or foreign bodies), normal clearing mechanisms are impaired, there is
pooling of secretions distal to the obstruction, and there is inflammation of
the airway. Conversely, severe infections of the bronchi lead to
inflammation, often with necrosis, fibrosis, and eventually dilatation of
airways.
cystic fibrosis. In this disorder, the primary defect in chloride transport
leads to impaired secretion of chloride ions into mucus, low sodium and
water content, defective mucociliary action, and accumulation of thick
viscid secretions that obstruct the airways. This leads to a marked
susceptibility to bacterial infections, which further damage the airways.
In primary ciliary dyskinesia, an autosomal-recessive syndrome, poorly
functioning cilia contribute to the retention of secretions and recurrent
infections that in turn lead to bronchiectasis. There is an absence or
shortening of the dynein arms that are responsible for the coordinated
bending of the cilia. Approximately half of the patients with primary ciliary
dyskinesia have Kartagener syndrome (bronchiectasis, sinusitis, and situs
inversus or partial lateralizing abnormality) . The lack of ciliary activity
interferes with bacterial clearance, predisposes the sinuses and bronchi to
infection, and affects cell motility during embryogenesis, resulting in the
situs inversus. Males with this condition tend to be infertile, owing to
ineffective mobility of the sperm tail.
Morphology. Bronchiectasis usually affects the lower lobes bilaterally,
particularly air passages that are vertical, and is most severe in the more
distal bronchi and bronchioles. When tumors or aspiration of foreign
bodies leads to bronchiectasis, the involvement may be sharply localized to
a single segment of the lung. The airways are dilated, sometimes up to four
times normal size. These dilations may produce long, tubelike
enlargements (cylindrical bronchiectasis) or, in other cases, may cause
fusiform or even sharply saccular distention (saccular bronchiectasis).
Characteristically, the bronchi and bronchioles are sufficiently dilated that
they can be followed, on gross examination, directly out to the pleural
surfaces. By contrast, in the normal lung, the bronchioles cannot be
followed by ordinary gross dissection beyond a point 2 to 3cm removed
from the pleural surfaces. On the cut surface of the lung, the transected
dilated bronchi appear as cysts filled with mucopurulent secretions.
The histologic findings:
there is an intense acute and chronic inflammatory exudation within the
walls of the bronchi and bronchioles,
associated with desquamation of the lining epithelium and extensive areas
of necrotizing ulceration.
There may be squamous metaplasia of the remaining epithelium.
In some instances, the necrosis completely destroys the bronchial or
bronchiolar walls and forms a lung abscess
Clinical Course. Bronchiectasis causes severe, persistent cough;
expectoration of foul-smelling, sometimes bloody sputum; dyspnea and
orthopnea in severe cases; and occasional life-threatening hemoptysis.
Obstructive ventilatory insufficiency can lead to marked dyspnea and
cyanosis. Cor pulmonale, metastatic brain abscesses, and amyloidosis are
less frequent complications of bronchiectasis.