asthma and cough reflex Flashcards
what is the cough reflex?
protective reflex to rid the airway of irritants
In a cough reflex, what are the 3 predominant nerve fibre receptors which detect irritants?
Rapidly adapting receptors (RARS)
Slow adapting receptors (SARS)
C fibres
What do C fibres repsond to?
chemical stimuli, inflammatory and immunological mediators
describe how a signal is sent to trigger the cough reflex
receptors detect the presence of irritants and respond by sending a signal via the Vagus nerve to the NTS in the medulla. Efferent nerve fibres are PHRENIC, vagus and recurrent laryngeal which transmits the impulse to effector muscles: diaphragm, intercostal, laryngeal, abdominal, bronchial smooth muscles.
describe the cough reflex
inspiratory phase: Rapid deep inhalation. Brough about by contraction of diaphragm and external intercostal muscles.
This increases the pressure inside the lungs.
Compression: glottis closes off the windpipe and inspiratory muscles relax. Contraction of expiratory muscles (internal intercostal and abdominal). Resulting in higher lung pressure. This all happens simultaneously.
expiratory phase: glottis opens and air is forcefully expelled out due to high pressure in the lungs.
define asthma
chronic inflammatory disorder of the airways
describe the possible triggers and causes of asthma
allergen occupational sensitisers pollen drugs (Beta blockers, NSAIDs) Viral infections Cold air Strong emotion Irritant dusts, vapours and fumes cigarette smoke exercise
describe the pathophysiology of asthma
Thickened basement membrane
Bronchoconstriction due to increased responsiveness of bronchial smooth muscle (histamine release)
Bronchial smooth muscle hypertrophy
Hypersecretion of mucus due to increased number of goblet cells + hyperplasia, leading to plugging of airways
Infiltration of bronchial mucosa by mast cells, eosinophils, lymphoid cells and macrophages.
Necrosis of airway epithelium
Subepithelial collagen deposition in long-standing cases
Airway occlusion
increased number of blood vessels (angiogenesis)
what are the 3 main characteristics of asthma?
Airway hyper responsiveness
Airway obstruction
Bronchial inflammation
What is the difference between TH1 and TH2 cells?
TH1: promotes inflammation by increasing cell mediated immunity
TH2: promotes inflammation by increasing humoral immunity
In asthma which T helper cells are upregulated more?
TH2
Describe the pathogenesis of asthma
Allergen is engulfed by Antigen Presenting Cell and fragment is presented to T-lymphocytes. T lymphocytes can differentiate into either TH1 or TH2 cells. Asthmatics have more TH2 cells.
TH2 cells stimulate plasma cells via IL13 and IL4 to produce IgE antibodies. Through IL5, TH2 cells stimulate eosinophil production which release inflammatory cytokines and leukotrienes.
Allergen binds to IgE which binds to mast cells and the IGE/mast cell complex triggers histamine, leukotriene and prostaglandin release to stimulate an inflammatory response. This causes broncho constriction
Risk factors for asthma
Smoking family history Air Pollution Occupational sensitisers Allergies respiratory infections Obesity
List the symptoms of asthma,a
Cough (dry)
Wheezing (high pitched whistling sound coming from the airways)
Chest tightness
Breathlessness
Describe the management of asthma
Intermittent (no more than twice a week): Short Acting Beta Agonist
Mild persisting (more than twice a week but not everyday): SABA + low dose steroid
IF LOW DOSE steroid is not working, then consider adding LTRA.
Moderate persistent (daily symptoms): LABA + low dose steroid
Increase steroid dosage to medium if appropriate
Severe persistent asthma (symptoms throughout the day, night awakening maybe every night): LABA + high dose inhaled steroid. Could also use Leukotriene Receptor Antagonist instead of LABA
