commensals of upper respiratory tract

Question 1

List common bacteria of upper respiratory tract

Answer 1

Streptococcus
Actinobacillus
Pasteurella multocida
Bordetella bronchiseptica
Escherichia coli

Question 2

What makes bacteria commensal vs pathogenic

Answer 2

Location on host
Acquisition of virulence genes
Change in gene expression
Host specific
Host controls impaired

Question 3

What are the specific and non-specific ways of removing foreign agents from respiratory tract

Answer 3

Non-specific (removal of particles):
Physical & anatomical (e.g. head position, cilia)
Lubricants (e.g. mucus)
Reflexes (e.g. coughing & sneezing)
Antimicrobial compounds (e.g. lysozyme)

Specific (recognition of particles by immune system):
Passive immunity (e.g. vaccination)
Lymph nodes/tissues
Innate immune system
Mucosal immunity (antibodies & lymphocytes)

Question 4

How does sneezing/coughing defend the respiratory tract

Answer 4

To remove foreign objects/irritants

Sneeze reflex:
Upper resp tract
Clears nasal passages

Cough reflex:
Lower resp tract
Clears trachea & bronchi

Question 5

What are the antimicrobial compounds that defend the respiratory tract

Answer 5

Defensins:
Short chains of amino acids
Produced by macrophages, neutrophils & epithelium
Kill bacteria, fungi & enveloped viruses

Lysozyme:
In mucous
Anti-bacterial enzymes
Break down of bacterial cell walls

Question 6

What are the main lymph nodes that drain the head and respiratory tract

Answer 6

Head:
Parotid
Mandibular
Retropharyngeal

Thorax:
Tracheobronchial

Question 7

Describe the fate on inhaled particles in the upper respiratory tract

Answer 7

Trapped in mucus & transported via mucociliary escalator
–> swallow

Stimulation of receptor/reflexes: sneeze or cough/glottis closure
–> swallow

Stimulation of immune responses/antimicrobial agents in mucus/secretions
–> killed

Question 8

What alveolar leucocytes are found in healthy & diseased respiratory tract

Answer 8

Healthy lung:
Macrophages
Lymphocytes
Occasional neutrophils
Low level of mucus

Diseased lung:
Macrophages
Lymphocytes
Frequent neutrophils (neutrophilia)
Excess mucus
Hemosiderophages (macrophages that have ingested red blood cells)

Question 9

What is bronchiolar spasm and what causes it

Answer 9

Bronchiolar spasm is sudden constriction of smooth muscles in wall of bronchioles

Causes:
Irritation (particles, fumes)
Infection
Allergy (e.g. equine or feline asthma)

Question 10

How do allergic reactions cause bronchospasm

Answer 10

Allergens themselves harmless but activate T & B cells

Activation of B cells leads to type I hypersensitivity reaction:
1. IgE antibodies formed when B cell first came in contact with allergen
2. IgE bind to mast cells/basophils in mucous membranes
3. If allergen encountered again, mast cells/basophils degranulate & release large amount of histamine & other inflammatory mediators
4. Inflammatory mediators lead to smooth muscle contraction around bronchioles
5. –> bronchoconstriction