L6. Control of Pulmonary airways

Question 1

What are the changes in SA, airflow and resistance along the respiratory airway tree

Answer 1

The cross sectional SA increases from trachea to alveoli x500. (funnel effect)
Therefore the resistance to airflow is greatest in trachea and decreases at the alveoli.
Therefore the air flow is fast and turbulent in the area of highest resistance and slow and laminar in alveoli for gas exchange

Question 2

Compare anatomical / physiological dead space

Answer 2

Dead space = space that plays no part in ventilation. It causes contamination of freshly inhaled air diluting the O2 content.
Anatomical dead space = conducting zone.
Physiological dead space: regions of the lung not ventilated properly/ not receiving blood flow.

Question 3

What are the physical mechanisms controlling airflow

Answer 3

-Upper airways have around 50-70% of the resistance generally due to SA.
When you exhale you have minimal radial traction but during inspiration, the respiratory zone airways are pulled open by their parenchyma which decreases resistance.

Question 4

What are the chemical mechanisms controlling blood flow

Answer 4

Bronchoconstriction is caused by Histamine (inflammation), SRS-A (slowly reacting substance of anaphylaxis and Pg F2a. (also smoke, dust, SO2).

Bronchodilation is caused by increased CO2 levels and Pg E

Question 5

What are the neural mechanisms controlling blood flow

Answer 5

Smooth muscle in the upper airways is innervated by ParaSymp and Sympathetic nerves.
Bronchoconstriction caused by Parasymp activation of muscarinic receptors using Ach.
Bronchodilation by Symp activation of B2 receptors by Na

Question 6

Describe the Cough reflex- autonomic reflex by vagal nerves

Answer 6

1. Irritant receptor activated by inflammatory mediators in larynx sends sensory signal to
2. Medulla Oblongata respiratory centres
3. Bronchoconstriction triggered by efferent Ach muscarinic receptors–> increasing airflow velocity by forced expiration to remove source of irritation.

Question 7

Describe the Hering-Breuer inflation reflex

Answer 7

1. Lung mechanoreceptor (stretch) is stretched during inflation sends vagal afferent to
2. Medulla oblongata respiratory centres which send
3. Sympathetic efferent to bronchioles to bronchodilate by Na to b2 receptor. It also terminates inspiration.

Question 8

What test is used to measure airway resistance

Answer 8

FEV1 / FVC. The FEV1 will be greater if there is less resistance. Normally the ratio is 80%.

Question 9

What is restrictive lung disease and what are some of the intrinsic vs extrinsic factors and although both FEV1/FVC are reduced from normal 4/5 L, which one reduces more

Answer 9

Caused by intrinsic: interstitial pulmonary fibrosis, asbestosis, tb or Extrinsic- NeuroM disease, obesity, diaphragmatic hernia, pleural thickening.
RLD is a restriction in lung expansion, resulting in decreased lung volume, increased work of breathing, therefore inadequate ventilation.
The decline in FVC is greater than in FEV1 so ratio is higher than 80%

Question 10

What is obstructive lung disease and what are some of the intrinsic vs extrinsic factors and although both FEV1/FVC are reduced from normal 4/5 L, which one reduces more

Answer 10

Due to an obstruction in the airways-
mucus, inflammation and easily collapsible airways or excessive constriction of airway SM due to smoke inhalation
Caused by asthma, bronchiectasis, COPD from smoking and CF.
FEV1 reduced more than FVC so ratio is lower than 80%

Question 11

What are the regional differences in ventilation within the lung and why

Answer 11

Greatest ventilation at the base of the lung because the alveoli at the top of the lung are larger than at the bottom so they have less capacity to inflate more. The smaller alveoli are more compliant. This is because intrapleural pressure is greater the top (more negative) due to gravity exterting positive force on the intrapleural space at the bottom so there is greater distension (suction force) of the alveoli