Pulmonary defence mechanisms Flashcards
(14 cards)
why are lungs a potential site of immunological vulnerability
-humans consume around 500L of oxygen per day, obtained from atmosphere around inhalation of 8000L of air per day. This process requires:
-fast movement of air from atmosphere to respiratory surfaces- places limit on filtering/barrier structures possible.
-efficient gas exchange- requires a thick membrane innervation by blood vessels, and a warm moist environment which most microorganisms thrive in.
explain different infections that can occur in the resp. system
-tuberculosis
-pneomonia
-aspergillosis
-bronchitis
-whooping cough
-measles
-asthma
-lung cancer
-occupational lung disease
-allergic rhinitis
-emphysema
explain what size/types of particles can air contain?
Large particles:
-foreign body aspiration
(e.g. food, liquid, choke hazards)
Fine particulate material:
-pollution (<2.5-1000um)
-dust (0.1-1000um)
-pollen (10-100um)
Microscopic pathogens:
-fungal scores (2-10um)
-bacteria (0.5-5um)
-viruses (>1um)
explain how the resp system has mechanisms that improve immunological defence
Physical obstructions:
-macro—> nasal hairs, turbinates, branching airways
-micro—-> cilia, mucous
protective reflexes;
-coughing, sneezing, expiratory reflex
immunological defence system;
-lung residant immune cells
-structural cells
-antimicrobial proteins
biological symboisis- commensals/microbiota
explain the adaptations of immunological defence organs
-Nasal hair and turbinates help filter air and prevent particles from reaching the airways.
-come into contact with tissue mucous/fluid so particles get stuck and filtered out before reach lungs
-cilia and mucus function to trap and remove microorganisms and particles.
cilia and mucus function to trap and remove microorganism and particles
what are the effects of loss/imairment of mucus-ciliary function
CFTR mutation —-> mucus dehydration + decrease airway surface fluid —> cilia dysfunction —> decrease mucus clearance
explain the process of mucus secretion
1) mucus ciliary clearance —> mucus constantly being pushed towards the throat from the airways where it can be swallowed into the GIT to be filtered by acid so particles trapped are then expelled.
2) cilia will have an adaptation so when the reverse stroke (move backwards) they curl up so overall width/depth it penetrates to mucus decreases in reverse stroke.
3) when it goes backwards its within perciliary layer which is more watery where mucus sits on top —> it moves forwards it extends forward deeper into the mucus layer and pushes it forward.
explain how the cilia and mucus function to trap and remove microorganism and particles
-requires one function cilia but also pericilliary layer of particular depth which is 4-6 microns healthily.
-if it becomes shallower in cases like cystic fibrosis (dehydration of resp.surface) can get less deep so in reverse stroke.
-percilliary layer comes in contact with mucus layer so not as effective clearance of mucus
explain how protective reflexes remove irritant or harmful particles from the airways
1) coughing
2) laryngeal expiratory reflex
3) sneezing
explain the basic mechanism of protective mechanisms
1) the basic mechanism involves the activation of 2 afferent sensory neurones, which transmit the impulse to breathing centres within the brain.
2) efferent signals are then transmitted to specific respiratory muscles, the glottis and airways to initiate a coordinated respiratory effort which rapidly expels air from the nasal cavity/airways/lungs.
3) sneezing is initiated by stimulation of sensory receptors within the nasal cavity and involves a deep inspiration phase, a compression phase, and a final expiration phase where air is expelled
4) coughing involves 3 phases, but it 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.
5) The laryngeal reflex is short, forcible expiratory effect without a preceding inspiration, 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 upper respiratory tract.
-an initial inspiration before expiration is undesired in some circumstances as it could potentially lead to inspiration pneumonia
discuss how the branching structure of the airways also helps to filter particles
-the overall structural pattern of the airways acts to increase filtering of air and prevent particles from reaching lower respiratory structures.
-human airways branch approximately 23x between the trachea and alveoli.
-when inahled air reaches an airway branching site, airflow changes from laminar to semi-turbulant flow pattern.
-increasing particle deposition as more particles come into contact with the mucus lined airway wall
explain how the resident immune cells provide the last line of defence
1) alveolar macrophages (AM) are the resident phagocytes within the lung and develop from progenitors produced in the bone marrow that migrate to the lung.
2) AM are found within the airspace and phagocytose pathogens, foreign material and cell debris, digesting it into residual material that is subsequently removed by the lymphatic system
3) However certain particles cannot be digested and cleared by macrophages, triggering inflammation and tissue damage/fibrosis.
4) Macrophages constitute part of the innate immune system and help to trigger further inflammation and an adaptive immune system and help to trigger further inflammation and an adaptive immune response by secreting cytokines and other inflammatory mediators in response to Toll-like receptor stimulation.
5) Some macrophage populations can also act as antigen presenting cells, (presenting antigens to T cells to stimulate cell-mediated immunity, B cell antibody production).
6) However alveolar macrophages display very little capacity for this
explain how structural cells can initiate/coordinate immune responses
In addition to leukocytes, structural cells such as epithelial cells and fibroblasts also express pattern recognition receptors; secrete antimicrobial peptides and signal (via cytokine release) to initiate/coordinate immune responses
give a summary of the key points
1) inhaled air contains harmful particles of various sizes; fine particulates, microorganisms and allergens.
2) the respiratory system defensive adaptations include; physical barriers, mucociliary clearance, protective reflexes, and resident immune cells.
3) mucus traps inahled particles, contains antimicrobial peptides and is removed from the lun via coordinated cilia movement.
4) alveolar macrophages patrol the airspaces, removing particles, microorganisms and dead cells from respiratory surfaces via phagocytosis.
