pulmonary defence mechanisms Flashcards
why are the lungs a site of immunological vulnerability ?
- The human body consumes approximately 500 L of oxygen/day in order to produce the energy for basal metabolic rate + physical activity.
- This oxygen is obtained from atmosphere, which requires inhalation of approximately 8000 L of air/day
- Supplying this much oxygen requires movement of large volumes of air from the atmosphere to internal respiratory surfaces (and out again) via the airways, which itself necessities:
- Fast movement of air in and out of the lungs - this places limits on the level of filtering/barrier structures possible (e.g. the solution the GI tract uses – stomach acid – is not possible).
- Efficient gas exchange - requires a large surface area, a thin membrane at the gas-blood interface (delicate structures vulnerable to damage and infection), innervation by blood vessels, and a warm, moist environment to allow diffusion of respiratory gases (but in which microorganisms also thrive).
what potentially harmful organisms/particles does the air contain ?
- The air we breathe is not sterile - we share it with everybody/everything else in our contained environment
- air contains many potentially damaging (both living and inanimate) particles/organisms:
- Microorganisms – bacteria, viruses, fungi, helminths
- Allergens – dust, pollen
- Organic particles – occupational exposures, pollution
- Toxic gases – carbon monoxide, sulphur dioxide, nitrogen dioxide
what size/types of particle can air contain ?
Large particulates:
Foreign body aspiration (e.g. food, liquid, choke hazards)
Fine particulate material:
Pollution (<2.5 - 1000 μm)
Dust (0.1-1000 μm)
Pollen (10 - 100 μm)
Microscopic pathogens:
Fungal spores (2 - 10 μm)
Bacteria (0.5 - 5 μm)
Viruses (< 1 μm)
True or False: The respiratory system is only vulnerable to infection from inhaled microorganisms.
False
The respiratory system is also vulnerable to damage from inhaled particles such as pollution and allergens.
What are some examples of chronic lung diseases caused by long-term inhalation of organic particles?
- Fibrosis
- Interstitial lung disease
- Coalminer’s pneumoconiosis
These conditions result from the damaging effect of particle deposition and the immune response.
What adaptations does the respiratory system have to improve immunological defense?
- Physical obstructions: nasal hairs, nasal turbinates
- Protective reflexes: coughing, sneezing
- Immunological defense system: alveolar macrophages, epithelial cells, antimicrobial proteins, microbiota
These adaptations limit the risks of infection and exposure.
What role do nasal hairs and turbinates play in respiratory defense?
- They filter air, preventing larger particles (>10μm) from reaching the airways
- The nasal turbinates/conchae are mucous membrane-lined, ridged structures within the nasal cavity that help to warm and humidify air before it reaches the airways/lungs, as well as help to filter out particles larger than ≈ 2μm.
Impairment of these structures is linked to increased asthma risk.
How does mucus function in the respiratory system?
Mucus ( secreted by goblet cells and submucosal glands) traps inhaled particles and microorganisms, contains antimicrobial proteins, and aids in their removal through ciliary action.
Mucus viscosity and color can indicate respiratory pathology.
describe the movement of cilia
- Under the mucus is a thin, watery periciliary layer (about 7μm deep). This layer is important because it allows tiny hair-like structures called cilia to move freely.
- Cilia are found along the airways, from the trachea to the smaller bronchioles. They beat in a coordinated rhythm to push mucus (and trapped particles) towards the throat, where it is swallowed or coughed out.
- Each cilium moves back and forth, but only touches the mucus during its forward stroke. During the backward stroke, it bends so its tip moves under the mucus. This way, the mucus is moved in one direction—out of the lungs and towards the throat—to keep the airways clear.
What are the three protective reflexes in the respiratory system?
- Sneezing - initiated by stimulation of sensory receptors within the nasal cavity and involves a deep inspiration phase (“ah….”), a compression phase (during which the glottis is closed, leading to pressure build-up), and a final expiration phase in which air is expelled (“….choo!”).
- Coughing - similarly involves these three phases, but is triggered by stimulation of receptors within the larynx and large airways. In contrast to sneezing, coughing can also be initiated voluntarily, and involves bronchoconstriction to further increase expulsion pressure.
- Laryngeal expiratory reflex - is a short, forcible expiratory effort without a preceding inspiration (differentiating it from coughing), triggered by stimulation of sensory receptors within the vocal folds. The role of this reflex is to prevent foreign bodies entering the airways, and to expel phlegm and the upper respiratory tract. An initial inspiration before expiration (such as with coughing) is undesired in some circumstances as it could potentially lead to inspiration pneumonia.
These reflexes help expel irritants and harmful particles from the airways.
How does the branching structure of the airways aid in filtering particles?
- The branching increases particle deposition by changing airflow from laminar to semi-turbulent when air reaches branching sites.
- particles are more likely to become trapped
This pattern enhances contact with mucus-lined airway walls.
what is the function of resident immune cells ?
last line of defence
What role do alveolar macrophages play in lung defense?
They phagocytose pathogens, foreign material, and debris, and secrete cytokines to initiate immune responses.
Certain particles cannot be digested by macrophages, leading to inflammation and tissue damage.
What is the significance of the airway/lung microbiota in immunological balance?
They help resist infection by other pathogens and modulate the immune system.
Understanding their role may lead to future treatment options.
Fill in the blank: The respiratory system’s ability to clear mucus is crucial for preventing _______.
respiratory infections
Impaired mucociliary clearance can lead to recurrent infections and inflammation.
What are the consequences of excessive mucus production in the airways?
It can obstruct airflow, leading to conditions like asthma and chronic bronchitis.
Mucus production can be influenced by local inflammation and nervous system stimulation.
