Aerosol is the collection of particles/lipid droplets which are small enough to remain suspended in the air for a period of time.
Aerosols suspended in air are inhaled
Aerosols are classified as inhalable/PM 10 (10µ or less) and respirable/PM 2.5 (2.5µ or less)
These inhaled particles are trapped by the moist surface of the tracheobronchial tree depends on the size of the particles.
Large particles (> 5µ) are trapped by inertial impaction
Inertial impaction occurs as bends in the large air ways
Large particles (> 5µ) travel at high velocity are unable to cross these bends.
Inertial impactions are provided by the lymphoid tissues in the tonsils, bronchi associated with lymphoid tissues.
Particles < 4µ settle down by means of sedimentation on the wall of the airways and remain in the lung for ever.
Particles that diffused into the alveoli epithelium are exhaled out.
Type of breathing alters the settlement of the particles in the respiratory tract
Slow, deep breathing transport the particles deep into the lung
Rapid, shallow breathing enhances inertial deposition in the air ways
Bronchoconstriction enhances the deposition in the central airways
Bronchodilatation favors peripheral deposition
Deposition of particles
Toxic gases get deposited based on their solubility and concentration
Highly soluble sulphur dioxide at lower concentration is removed by the nose, but at higher concentration it will go deep into the lung
Less soluble gases also go deep into alveoli
Inhalation of toxic gases initiates protective reflexes like cough, sneeze, high mucous secretion and bronchospasm.
Anatomical specialties of mucociliary blanket of the respiratory tract
It consists of sol and gel mucous layers overlying the epithelial cells
Particles deposited in the lung are transported by the mucociliary escalator to the pharynx for its swallowing
Sol layer is a low viscous layer over which the cilia beats and baths surface of the epithelial cells
Gel layer is more viscous that traps the inhaled particles
Forward beating of the cilia propels the particles to tracheobronchial system or nasal cavity
Rate of ciliary beating depends on the surface area and also gravity
Slow ciliary beating in the bronchiole than bronchi and trachea
Respiratory mucous secretion
Clara cells are the non ciliated portion of bronchioles in the smaller airways
Goblet cells are located in the large air ways secrete mucous
Bronchial glands also secrete serous and mucous via sub mucosal glands
Mucous secretions are under the influence of autonomic nervous system
On the surface of the epithelial cells, the microvilli assist the ions fluid exchange
The composition of the mucous varies with the nature of stimuli
During bacterial overload increased viscosity of mucous secretion, lesser the clearance rate
Transepithelial movements of water and ions changes the composition of the mucous layer
Cough reflex
It is a protective reflex initiated by irritation of the sub epithelial layer or stimulation of stretch receptors in the large bronchi by the foreign bodies
Inflammation of the air passage and injury to respiratory epithelium also causes hyper responsive cough reflex
It clears the mucous secretions from the trachea and large bronchi
