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Flashcards in Surface tension Deck (19):
1

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.

2

Describe the impact of surface tension on lung function.

1. 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)

3

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.

4

Describe surfactants impact on lung function

increases lung compliance, prevent collapse of small alveoli, and prevent the accumulation of fluid inside the alveoli

5

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.

6

list the different types of air-flow. Which is most common in airways

laminar flow, turbulent flow, transitional flow. Transitional flow is most common

7

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)

8

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.

9

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

10

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

11

List factors that can alter airway resistance

Lung volume, bronchial smooth muscle tone and dynamic airway collapse

12

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

13

Describe lung volume in people with increased airway resistance

They breathe at high lung volumes to reduce the resistance and expand airways

14

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.

15

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.

16

Mechanisms of bronchial smooth muscle dilation

Bronchodilation occurs in response to stimulation of adrenergic receptors by epi and NE (Beta2 receptors), high CO2 pressure and isoproterenol or albutenol (Beta AR agonists).

17

Define dynamic airway collapse and its effect on expiration

Intrapleural pressure is usually negative, which makes transpulmonary pressure positive and the airway stays open. If intrapleural pressure becomes positive(such as suring forced expiration), it can result in a negative transpulmonary pressure, and the airways can collapse.

18

Describe airway collapse in emphysema patients

Patients with emphysema have a much higher tendency to have airways collapse, even during quiet expiration. They have reduced tendency of lung recoil (due to higher lung compliance) and they are likely to employ expiratory muscles even during quiet breathing. They also have a loss of supporting connective tissue in the airway which makes them more prone to collapse

19

How to emphysema patients expire

with pursed lips to keep airways open