Surface tension Flashcards
What is surface tension
Surface tension is a property of the water
that lines the inner surfaces of alveoli. Water molecules form attractive interactions, while they form relatively unfavorable interactions with air. Because of these
favorable/unfavorable interactive forces, a tension develops at the interface between liquid and
air. Surface tension is a property of the water
that lines the inner surfaces of alveoli. Water molecules form attractive interactions, while they form relatively unfavorable interactions with air. Because of these
favorable/unfavorable interactive forces, a tension develops at the interface between liquid and
air.
Describe the impact of surface tension on lung function.
- Reduced lung compliance (surface tension in smaller alveoli produces a net force that opposes expansion of alveoli) 2. Fluid accumulation in alveoli (fluid movement into alveoli reduces liquid-air interfaces). 3. Collapse of small alveoli (the smaller the radius, the higher the interal pressure which would lead small alveoli to empty their air into larger ones and collapse)
Describe the physical properties of surfactant and its functions
Surfactant is a mix of lipids and proteins secreted by type II cells. It intercalates btw water molecules and reduces the attractive forces, thus lowering the surface tension of water. Efficacy increases at smaller alveolar radii because the concentration of surfactant incrases as surface area becomes smaller.
Describe surfactants impact on lung function
increases lung compliance, prevent collapse of small alveoli, and prevent the accumulation of fluid inside the alveoli
Respiratory distress syndrome
Surfactant deficiency: Affected infants have stiff, noncompliant lungs that are prone to collapse. Surfactant begins to be produced at fetal-week 24, which is about the earliest age pre-term infants can survive.
list the different types of air-flow. Which is most common in airways
laminar flow, turbulent flow, transitional flow. Transitional flow is most common
Describe laminar flows relation to airway resistance
Laminar flow: At low flow rates, air flows in stream-lines that are parallel to the sides of the tube. Flow rate is proportional to pressure difference. Resistance= (8nl)/(pi r^4)
Describe turbulent flows relation to airway resistance
Turbulent flow occurs as flow rate increases and flow rate is proportional to the square root of the pressure difference. It is less efficient than laminar flow. Turbulence depends on the velocity, gas density, radius and viscosity.
Describe transitional flows relation to airway resistance
In the airways, with the complex geometry of the bronchial tree, its many branching points, changes in diameter, and irregular wall surfaces, we describe the situation as one of transitional flow
where in the airway is the major site of airway resistance
intermediate sized bronchi. There is relatively litle resistance in the terminal bronchioles due to the large number of small bronchioles
List factors that can alter airway resistance
Lung volume, bronchial smooth muscle tone and dynamic airway collapse
How does lung volume alter airway resistance
Airways expand at large lung volumes and the resistance decreases. At smaller lung volumes, the airways are narrower and their resistance is greater. Bronchioles are most sensitive to lung volume b/c they do not have cartilage
Describe lung volume in people with increased airway resistance
They breathe at high lung volumes to reduce the resistance and expand airways
how does bronchial smooth muscle tone alter airway resistance
Contraction of the bronchial smooth muscle narrows the
airways and increases the resistance.Contraction of the bronchial smooth muscle narrows the
airways and increases the resistance.
Mechanisms of bronchial smooth muscle contraction
bronchial smooth muscle contracts in response to Vagus nerve innervation (induces bronchoconstriction via release of acetylcholine), histamine, arachidonic acid metabolism products, low CO2 pressure.
