pulmonary ventilation

Question 1

How does the pleural and alveolar pressure change during inspiration/ expiration?

Answer 1

Pleural pressure = pressure of the fluid in the space between the pleural surface of the lungs and the pleural surface of the chest
Alveolar pressure = pressure within the alveoli

Inspiration: pleural pressure decrease, alveolar pressure decrease
Expiration: pleural pressure increase, alveolar pressure increase

Question 2

What’s the main driving force behind transpulmonary pressure?

Answer 2

Transpulmonary pressure = difference between the pleural and alveolar pressure
2/3 of it is due to the elastic forces caused by surface tension (the remainder = elastic forces due to the lung tissues)

Question 3

What are the 3 factors that keep the small alveoli open?

Answer 3

1. interdependence - they share common airways/ septa
2. fibrous tissue - the fibrous septa provide additional control
3. surfactant - greatly reduces the surface tension, allows for interdependence and fibrous septa to be more effective

Question 4

Define the 4 different pulmonary volumes.

Answer 4

1. tidal volume: normal respiration volume (inspiration + expiration)
2. Inspiratory reserve volume: extra inspired air above and beyond the normal inspiration volume
3. Expiratory reserve volume: extra air above and beyond the normal expiration and can be exhaled
4. Residual volume: the volume of air that remains in the lung after maximum exhalation

Question 5

Define the 4 different pulmonary capacities.

Answer 5

1. Inspiratory capacity: tidal volume + inspiratory residual volume = maximum amount of air that can be inhaled
2. Functional residual capacity: residual volume + expiratory reserve volume = amount of air that remains in the lungs after normal exhalation
3. Vital capacity: inspiratory reserve volume + tidal volume + expiratory reserve volume = maximum amount of air that can be moved in and out
4. Total lung capacity: vital capacity + residual volume = maximum volume of which the lungs can expand to after greatest inspiration volume

Question 6

Define minute respiration and alveolar ventilation.

Answer 6

Minute respiration = breaths/min x tidal volume. This is the amount of new air that is moved into the respiratory passage per minute

Alveolar ventilation = amount of air that is engaged in gas exchange per minute. Takes into account of dead space
= breaths/min x (tidal volume - dead space)

Question 7

What are the 3 types of dead space?

Answer 7

1. anatomical: the parts of the respiratory passage that are not engaged in gas exchange
2. alveolar: the parts of the alveoli that is not engaged in gas exchange (close to zero in normal people)
3. physiological dead space = anatomical + alveolar

Question 8

Where is the greatest resistance to airflow in the respiratory passage in normal vs diseased setting?

Answer 8

• normally, it’s the major bronchi - though it has the biggest diameter, it also has the greatest air flow compared to the minute amount of air that goes through the tiny bronchioles
• however, in diseased state, it will be the small terminal bronchioles that will cause the most issues because:
  1. they are easily occluded due to their size
  2. they are easily constricted due to the relative high proportion of the smooth muscles vs their diameter

Question 8

How is constriction/ dilation of bronchioles controlled?

Answer 8

1. bronchodilation
   - very few sympathetic nerves penetrate the center of the lungs
   - but the bronchioles are all exposed to epinephrine and norepinephrine
   - especially sensitive to epinephrine due to that greater stimulation of beta adrenergic receptors –> dilation of the bronchial tree
2. bronchoconstriction
   - parasympathetic nervous system –> vagus nerve –> acetylcholine –> bronchoconstriction
   - use atropine to dilate

Question 8

What’s the importance of smooth muscles in the walls of the respiratory passage?

Answer 8

• the walls of the trachea and bronchi are mostly made of smooth muscles, when not cartilaginous
• the wall of the bronchioles = almost entirely covered in smooth muscles, except for the terminal bronchioles
• this is important as obstructive disease is due to excessive constriction of the smooth muscles, of which the bronchioles would be most affected

Question 9

What’s the function of mucus?

Answer 9

to moisten and entrap small particulate

Question 10

What’s the function of ciliated epithelium?

Answer 10

Ciliated epithelium is found in the entire reparatory passage, down to the terminal bronchioles
- functions to bring the mucus towards the pharynx –> coughed up or swallowed

Question 11

Which cells produce surfactant?

Answer 11

type 2 epithelial cells