3.2 lung mechanics Flashcards
(46 cards)
What is the pleura ?
a continuous double layered membrane which surrounds the lungs
Which surfaces are the pleura in contact with ?
contact with cavity wall = parietal layer
layer on lung surface = visceral layer
What are the lungs and chest wall ‘locked together’ by ?
intrapleural fluid in the intrapleural space
Ventilation is the process of ….?
air flowing by bulk flow into the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation)
why does air flow in bulk ?
because od pressure difference between the atmosphere and the gases inside the lungs
During inspiration what is responsible for the following ?
1. increasing the volume of the thorax
2. decreasing the pressure
- ribs and sternum raised
- diaphragm contracts
During expiration what results in the following ?
1. decreasing the volume of the thorax
2. increasing the thoracic pressure
- ribs and sternum lower
- diaphragm relaxes
What does the elasticity of lung tissure reduce ?
energy required during expiration (elastic recoil )
In inspiration following the expansion of the chest cage what is enough to hold the 2 layer of pleura firmly together ? [change Q]
expansion of chest cage pulls outwards on the lungs and intrapleural pressure becomes more negative. This small negative pressure is enough to hold the two layers of pleura firmly together
split Q above !!!
What is forced expiration ?
active process dependent on the abdominal muscles and internal intercostal muscles
What conditions is forced expiration affected in ? & why ?
- pregnancy & obesity cos diaphragm can’t easily move
- COPD & asthma due to narrowing of airways
what 2 factors cause the lungs to recoil during expiration ?
- elastic connective tissue in the lungs
- alveolar surface tension
what is alveolar surface tension?
attraction between water molecules at the water-air interface
What is equation for laplace’s law ?
P = 2T/ r
P = inward directed collapsing pressure
T = surface tension
r = radius
why are collapsed alveoli hard to reinflate ?
walls tend to stick together
What are septal cells ?
type II penumocytes that produce surfactant
found in the septa between alveoli
what is surfactant ?
a phospholipoprotein dissolved in a watery secretion that lines the alveolar sac
reduces the surface tension in the alveoli and stops the alveoli collapsing during expiration
What’s the difference between smaller and larger alveoli during inspiration and expiration with and without surfactant ?
without:
During expiration smaller alveoli collapse completely , larger alveoli change little
with:
during expiration both alveoli decrease proprtionately in size, alveoli shrink evenly during expiration
What is respiratory distress syndrome of a new born ? [shorten !]
foetal lungs unable to synthesise surfactant until late in pregnancy so premature babies may not have enough pulmonary surfactant
so lungs are hard to inflate and some alveoli may fail to open at all during inspiration
baby has to make very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
If the pleural cavity is damaged/ruptured where does air enter ?
pleural space because pleural pressure is less than atmosphere
Differences between atmospheric pressure and alveolar pressure to result in the following ?
1. no airflow
2. airflow into lungs
3. airflow out of lungs
What may lead to pneumothorax ? [alter Q !]
when intrapleural pressure becomes equal to or exceeds the atmospheric pressure and the pressure surrounding the lungs will increase and lungs may collapse
what is pleuritis or pleurisy ?
parietal pleura can become inflamed causing pain
