Pulmonary Host Defence - Dr Sunil Sharma Senior Resident...

Dr Sunil Sharma
Senior Resident
Dept. of Pulmonary Medicine

`
major function of the respiratory system is to major function of the respiratory system is to
procure O
2
& to eliminate CO
2
from the body
at rates required by tissue metabolism
`
Ambient inspired air along with O contains Ambient inspired air along with O
2
contains
noxious gases and a multitude of particulates
including viable microorganisms
Toxic substances in air are derived from
`
Toxic substances in air are derived from
many sources

`
naturally occurring processes can give rise to naturally occurring processes can give rise to
large amounts of aerosolized particles including
◦ resuspension of soil
◦ emissions from volcanic activity
◦ forest fires, photochemical reactions etc.
Ai b i l l i l d bi l i ll
`
Airborne particles also include biologically
derived viruses, bacteria, fungi, algae, spores,
and pollens
`
Industrial and occupational sources add SO
2
,
CO NO NH O hydrocarbons & inorganic and CO,NO
2
, NH
4
,O
3,
hydrocarbons & inorganic and
organic particles to the inspired air

`
Upper and lower airways represent the largest Upper and lower airways represent the largest
epithelial surface exposed to the outside
environment
`
Size of alveolar surface is that of a tennis court
`
To allow gas exchange foreign substances and
microorganisms must be stopped and removed
without inducing inflammation
`
variety of defences exists to protect host from
the harmful effect of microorganisms & air
pollutants

Airways and their mucosa
`
Luminal defence mechanisms
◦ Anatomical barrier
◦ Cough
◦ Mucociliary clearance
`
Blood derived cells of the
mucosa
◦ Dendritic cells
◦ Lymphocytes (T-cells; cd; NK cells)
◦ Secretory IgA
◦ Lysozymes, lactoferrins
◦ Defensins
Epithelial cells
◦ B lymphocytes
◦ Eosinophils; mast cells; basophils
`
◦ Epithelial barrier
◦ Mucin release
◦ Antimicrobial peptides
Alveolar spaces
`
Pneumocyte types I and II
Alveolar macrophages
◦ Bacterial receptors
◦ Chemotactic factors
◦ Growth factors; cytokines
`
`
Lymphocytes
`
Neutrophils
`
IgG and opsonins
`
Surfactant

Anatomical barrier
`
nose is efficient upper airway defence mechanism
that removes most airborne particles and water-
soluble gases from inspired air
`
Air entrained through the nasopharynx is subject to
filtration through tortuous epithelial passages
`
foreign particles of ≥ 10 μ m effective diameter are
ffi i tl d & l h i i t i t i efficiently removed & nasal hairs assist in trapping
larger inhalants
`
sneezing is an effective means of expelling some of
airborne contaminants

`
Microbes deposited into & attempting to colonize the Microbes deposited into & attempting to colonize the
nasopharynx has to compete against a dense flora of
nonpathogenic endogenous bacteria
`
Ciliated mucosal lining of the posterior nasopharynx
propels mucus and trapped foreign material into the propels mucus and trapped foreign material into the
oropharynx
b i b i d i h li d h
`
bacteria become mixed with saliva and are then
swallowed or expectorated
`
Anatomic barriers of the epiglottis and vocal cords
make aspiration into the trachea physically difficult