PAC3421 Study Guide - Final Guide: Antidiarrhoeal, Antispasmodic, Motility
23 Jun 2018
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Cystic fibrosis:
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
There are 3 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
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