PAC3421 Study Guide - Final Guide: Mucociliary Clearance, Cough Reflex, Respiratory Tract Infection
21 Jun 2018
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In cystic fibrosis there is a genetic defect in the production or expression of a particular transporter. Explain why this
is an issue in the airways. What cells and processes are affected and how does this reduce respiratory function?
In cystic fibrosis, lack functional membrane Cl- transporters means reduced outward movement of Cl- from airway
epithelial cells. This results in increased Na+ levels within the cell because Na+ ions normally passively follow Cl-
ions. As water follows Na+ out of the cells, the salt-water imbalance results in dehydrated and thickened secretions
(the luminal watery layer is diminished)
As a result, ciliated epithelial cells cannot beat effectively, the mucus escalator is dysfunctional and mucociliary
clearance is impaired. The accumulation of thick and dry mucus causes narrowed airway diameter, thereby
increasing airway resistance and creating obstruction to airflow which further impairs efficient gaseous exchange
process.
Furthermore, impaired mucociliary clearance allows persistent bacterial infiltration to cause chronic infection,
inflammation and tissue damage. The situation is made worse when defence proteins within the airway epithelial cells
are inactivated by high Na+ levels,
Note: In chronic bronchitis patients, CF will make the situation worse by causing “chronic bronchitis” to be progressed
into “bronchiectasis - i.e. localised irreversible dilation of the bronchial tree” and ultimately respiratory failure!
Pathophysiology & Pharmacology of Respiratory Diseases
Name three protective reflexes.
1. Mucus
-A viscoelastic gel containing water, HMW cross-linked glycoprotein, antimicrobial and antiinflammatory substances
-Colour of sputum cannot be used to differentiate between viral and bacterial infections
-Green sputum is due to the presence of myeloperoxidase (i.e. an enzyme found in neutrophils)
-However, greenness of sputum correlates with sputum bacterial count in COPD patients (because we already know
COPD patients definitely have bacterial infections and neutrophils)
-Mucus secretion mediated by parasympathetic nervous system
2. Cough
●Divided into productive and unproductive cough
●Productive cough is beneficial
○Caused by abnormal production of bronchial secretions
○Loosen and expectorate excess mucus from lower respiratory tract
●Unproductive cough has no benefit
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Document Summary
In cystic fibrosis there is a genetic defect in the production or expression of a particular transporter. Explain why this is an issue in the airways. In cystic fibrosis, lack functional membrane cl- transporters means reduced outward movement of cl- from airway epithelial cells. This results in increased na+ levels within the cell because na+ ions normally passively follow cl- ions. As water follows na+ out of the cells, the salt-water imbalance results in dehydrated and thickened secretions (the luminal watery layer is diminished) As a result, ciliated epithelial cells cannot beat effectively, the mucus escalator is dysfunctional and mucociliary clearance is impaired. The accumulation of thick and dry mucus causes narrowed airway diameter, thereby increasing airway resistance and creating obstruction to airflow which further impairs efficient gaseous exchange process. Furthermore, impaired mucociliary clearance allows persistent bacterial infiltration to cause chronic infection, inflammation and tissue damage.
