the mechanisms of breathing

Question 1

what does the rate of airflow depend on ?

Answer 1

• increased resistance = decreased airflow
• increased pressure gradient = increased airflow
• decreased airway radius = increased resistance = decreased airflow

Question 2

what is lung compliance ?

Answer 2

• how easily the lungs expand
• Higher lung compliance = less expansive force is required to inflate the lungs = ↑ volume change per transpulmonary pressure change (indicated by a greater [steeper] gradient on volume-pressure curves)
• Lower compliance = more expansive force is required to inflate the lung = ↓ volume change per transpulmonary pressure change (indicated by a lower [shallower/less steep] gradient on volume-pressure curve)

Question 3

how is lung compliance calculated ?

Answer 3

Cl = change in volume / change in pressure

Question 4

what factors and diseases affect lung compliance ?

Answer 4

• chest wall mechanics - scoliosis , obesity - decrease lung compliance
• alveolar surface tension - decrease compliance
• elastin fibres - fibrosis - decrease compliance , emphysema - increase lung compliance

Question 5

how is surface tension created within the alveoli ?

Answer 5

• created by the Prescence of a bubble like structure within the alveoli due to the structure of alveoli which is filled with air and lined by fluid
• H bonds between the fluid molecules exerts a collapsing force towards the center of the bubble.

Question 6

what is the potential problem caused by this surface tension ?

Answer 6

• smaller bubbles generates higher pressure than larger ones so smaller bubbles will empty into larger ones due to the pressure gradient.
• this will cause smaller alveoli to collapse making inflation of the lungs difficult

Question 7

what is the purpose of pulmonary surfactant ?

Answer 7

• reduces surface tension of air-liquid interface
• phospholipoprotein secreted by type II pneumocytes (alveolar cells).
  *Surfactant molecules are amphipathic, with hydrophilic head and hydrophobic tail regions, and so will naturally position themselves at the air-liquid interface.
  *The presence of the surfactant molecules then acts to disrupt the attractive forces between water molecules, reducing surface tension and the collapsing pressure generated.
• as alveoli expand number of surfactant molecules decreases increasing surface tension now larger alveoli collapse into smaller ones helping consistent inflation of the lungs

*Surface tension produced at the air-liquid interface also reduces hydrostatic pressure. Fluid is then pulled out of surrounding capillaries and into the alveoli.
By reducing surface tension, pulmonary surfactant helps to prevent alveolar oedema, as observed in patients with insufficient surfactant.

Question 8

what is neonatal respiratory distress syndrome ?

Answer 8