Surfactant, Compliance and Lung Function Tests Flashcards
Type I alveolar wall cells
thin walled cells that permit gas exchange
Type II alveolar wall cells
secrete surfactant fluid
Surfactant
detergent-like fluid produced by alveolar type II cells
Surfactant function
reduced surface tension on alveolar surface membrane (therefore reducing the tendency for the alveoli to collapse)
increases lung compliance
reduced lung tendency to recoil
makes work of breathing easier
Surfactant is more effective in…
smaller alveoli
because surfactant molecules come closer together and therefore are more concentrated
Law of LaPlace
p = 2T/r
Surfactant production begins at
25 weeks gestation
complete at 36 weeks
Premature babies without surfactant can have
infant respiratory distress syndrome
Compliance
change in volume relative to change in pressure
High compliance is a
large increase in lung volume for a small decrease in ip pressure
Low compliance is a
small increase in lung volume for a large decrease in ip pressure
Pulmonary fibrosis
hardening
less compliance
inert fibrous tissues means effort of inspiration increases
emphysema
loss of elastic tissue means expiration requires effort
destruction of alveoli/ loss of elasticity
obstructive lung disease examples
emphysema
bronchitis
COPD
Influenza
Asthma
Fibrosis leads to a decrease in
compliance
obstructive lung disease
obstruction of air flow - especially on expiration
restrictive lung disease
restriction of lung expansion
Spirometry
static
measure the volume exhaled
Spirometry
dynamic
measure the time taken to exhale a certain volume
FEV 1 in healthy male
4 litres
FVC in healthy male
5 litres
FEV1 / FVC ratio
80%
FEV1/FVC in obstructive disease ratio
lower
FEV1/FVC in restrictive disease ratio
higher or the same
Obstructive
rate at which air is exhaled is much slower
FVC (total expired volume) is also reduced
ratio is also reduced
Alveolar Ventilation
volume available for exchange in the alveoli
Pulmonary (minute) ventilation
product of tidal volume and respiratory frequency
Compliance is determined by…
elastic forces
surface tension at the alveolar air-liquid interface
airway resistance
Restrictive lung disease examples
pulmonary fibrosis
oedema
pneumothorax
infant respiratory distress syndrome
