Page 211 - 84 human physiolofy part-1

The Respiratory System

a condition where fibrous tissue builds up in the lungs. This makes it so our lungs cannot inflate
properly and are always tending toward deflation.

Asthma
Asthma is a respiratory disease of the bronchi and bronchioles. The symptoms include wheezing,
shortness of breath, and sometimes a cough that will expel mucus. The airways are very sensitive
to irritants which can include pollen, dust, animal dander, and tobacco. Even being out in cold air
can be an irritant. When exposed to an irritant, the smooth muscle in the bronchioles undergoes
spasms. Most asthma patients have at least some degree of bronchial inflammation that reduces
the diameter of the airways and contributes to the seriousness of the attack. While asthma is not
curable, it IS treatable.

Respiratory Distress Syndrome

• Pathophysiology

At birth the pressure needed to expand the lungs requires high inspiratory pressure. In the presence
of normal surfactant levels the lungs retain as much as 40% of the residual volume after the first breath
and thereafter will only require far lower inspiratory pressures. In the case of deficiency of surfactant
the lungs will collapse between breaths, this makes the infant work hard and each breath is as hard as
the first breath. If this goes on further the pulmonary capillary membranes become more permeable,
letting in fibrin rich fluids between the alveolar spaces and in turn forms a hyaline membrane. The
hyaline membrane is a barrier to gas exchange, this hyaline membrane then causes hypoxemia and
carbon dioxide retention that in turn will further impair surfactant production.

• Etiology

Type two alveolar cells produce surfactant and do not develop until the 25th to the 28th week of
gestation, in this, respiratory distress syndrome is one of the most common respiratory disease in
premature infants. Furthermore, surfactant deficiency and pulmonary immaturity together leads to
alveolar collapse. Predisposing factors that contribute to poorly functioning type II alveolar cells in a
premature baby are if the child is a preterm male, white infants, infants of mothers with diabetes,
precipitous deliveries, cesarean section performed before the 38th week of gestation. Surfactant
synthesis is influenced by hormones, this ranges form insulin and cortisol. Insulin inhibits surfactant
production, explaining why infants of mothers with diabetes type 1 are at risk of development of
respiratory distress syndrome. Cortisol can speed up maturation of type II cells and therefore
production of surfactant. Finally, in the baby delivered by cesarean section are at greater risk of
developing respiratory distress syndrome because the reduction of cortisol produced because the lack
of stress that happens during vaginal delivery, hence cortisol increases in high stress and helps in the
maturation of type II cells of the alveoli that cause surfactant.

• Treatment

Today to prevent respiratory distress syndrome are animal sources and synthetic surfactants, and
administrated through the airways by an endotracheal tube and the surfactant is suspended in a saline
solution. Treatment is initiated post birth and in infants who are at high risk for respiratory distress
syndrome.

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