Flashcards in Mechanics Of Breathing And Gas Exchange Deck (37)
What is the term for the stretchiness of the lungs?
Give some features of lung fibrosis
Low compliance, stiff lungs
Exposed to asbestos/coal dust
Collagen laid down
Stops elastin moving
Lungs cannot fill very much
Give some features of emphysema
Loss of elasticity, high compliance
More air into lungs
No elastic recoil as elastin has been destroyed by elastases
Expiration is difficult
Give some factors that decrease lung compliance
Laparoscopic surgical interventions (increased abdo pressure)
Severe restrictive pathologies
Hydrothorax (pleural effusion)
High standing of diaphragm (obesity, pregnancy)
What is surface tension?
The water molecules of the lining fluid of the lungs attract each other (H bonds)
The interface of air and fluid makes the surface resistant to stretching
(Why we need surfactant)
Why do we need lining fluid in the lungs?
To be able to move gases
Why do we have surfactant in the lungs?
To reduce the surface tension
Is a detergent that interrupts the H bonds
Makes the alveoli easier to inflate
What are the constituents of surfactant?
Where is lung surfactant produced?
Type 2 pneumocytes
(Simple cuboidal epithelial cells)
Surfactant works better for: bigger or smaller breaths?
Quiet breathing uses less energy
What is Laplace's law for working out the pressure inside a bubble?
Pressure = (2 x surface tension) / radius
Define the law of bubbles
If a big bubble is connected to a small bubble, air will flow from the higher pressure (small bubble) into the lower pressure (big bubble). Therefore the small bubble will collapse into the big bubble.
How does surfactant help to keep alveoli open?
Equalises the pressure between different sized alveoli so that they do not collapse into each other
Parts of the lung collapsing
Describe infant respiratory distress syndrome
Babies born prematurely (<36 weeks) have too little surfactant
Lungs are very stiff
Few, very large alveoli
Surfactant is dripped into the lungs and the baby is put on a low pressure ventilator
Why don't you put the infants with RDS on a high pressure ventilator?
Would cause the lungs to rupture or pneumothorax
Describe adult RDS
Not due to a lack of surfactant
More difficult to treat because of the widespread inflammation in the lungs
What different factors are taken into account in Fick's first law of diffusion?
Solubility of gas in solution
Cross sectional area of fluid
Distance molecules most travel
Molecular weight of the gas
Temperature of the fluid
How much more soluble in CO2 than O2?
20x more soluble
The diffusion coefficient is proportional to:
Solubility / square root of molecular weight
What is the equation for permeability?
(Diffusion coefficient x solubility) / thickness of the membrane
At 37'C what is the partial pressure of H2O in inspired air?
What happens to carbon dioxide when it enters the RBCs?
Reacts with water to form carbonic acid
Dissociates to form bicarbonate ions and H+ ions
Bicarbonate moves into plasma
H+ buffered by Hb
How is carbon dioxide carried in the blood?
90% carried as bicarbonate ions in the plasma
5% carried as dissolved CO2 in plasma
5% carried as carboxyhaemoglobin on proteins
What is the partial pressure of oxygen in alveolar air?
What is the partial pressure of carbon dioxide in the alveoli?
What are the approximate partial pressures of oxygen and carbon dioxide in normal air?
Oxygen = 20.8 kPa
Carbon dioxide = 0.04 kPa
What fraction of the time that the blood is in the pulmonary capillaries is required for gas exchange?
What is the approximate surface area of the lungs?