Respiratory 1

Question 1

Explain the balance that results in sub-atmospheric intraplural pressure in inhalation

Answer 1

Elastin in the alveoli acts as an inward collapsing force- elastic recoil, which is opposed by the elastic recoil of the ribs acting as an outward expanding force

Question 2

A lung with high compliance is

Answer 2

easy to distend - low elasticity

Question 3

Describe the relationship between compliance and elasticity

Answer 3

Inversely proportional

Question 4

What is the equation for compliance

Answer 4

Compliance = total volume / total pressure

Question 5

Describe the effect of surface tension on an alveolus

Answer 5

Surface tension resists stretch

• more surface tension = compliance is reduced
• alveolus becomes smaller
• Tends to recoil after stretch (contributes to elastic recoil pressure)

Question 6

Contrast the effect of inflating lungs with water and air (with ref to surface tension)
(graph slide 14)

Answer 6

Lung requires greater trans-pulmonary pressure to inflate with air in order to overcome surface tension + elastic
recoil effect

Question 7

Explain how surface tension creates a relationship showing hysteresis between inhalation and exhalation

Answer 7

• During the first part of inhalation, the input of energy needed to overcome surface tension is high
• During exhalation less energy is expanded due to elastic and surface tension recoil
• Breathing costs more energy on one loop of the ventilation cycle than the other
• Showing HYSTERESIS, revealed as a lag phase due to the surface tension effect during inhalation

Question 8

What size of alveolus have a higher surface tension ? (larger or smaller?

Answer 8

Smaller

Question 9

What is the law of Laplace?

Answer 9

Pressure in the bubble = 2T/r

T = surface tension & r = radius of bubble

Question 10

What is pulmonary surfactant composed of?

Answer 10

Dipalmitoyl phosphatidyl choline (DPPC) packaged around surfactant proteins (A-D)

Question 11

What secretes pulmonary surfactant

Answer 11

Type II alveolar epithelial cells

Question 12

What effects does pulmonary surfactant have?

Answer 12

• Reduces surface tension
• Reduces the pressure require to inflate lungs
• Prevents collapse of alveoli during lung expansion and contraction

Question 13

How does the radius of an alveoli effect surface tension?

Answer 13

As r falls, surfactant molecules crowded together, surface tension reduced. Smaller alveolus stabilised.

Question 14

What is a static force that influences breathing

Answer 14

Mechanical properties of the lung that influence gas flow but which are independent of volume change