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Physiology

Respiratory

Question 113 of 180

A 55 year old women presents to ED with a chronic cough. Which of the following pulmonary receptors is likely to be involved in causing her cough:

Answer:

Irritant receptors are located throughout airways between epithelial cells, with rapidly adapting afferent myelinated fibres in the vagus nerve. Receptors in the trachea lead to cough, those in the lower airway to hyperpnoea. Stimulation also causes reflex bronchial and laryngeal constriction. Irritant receptors are stimulated by irritant gases, smoke and dust, rapid inflation/deflation, airway deformation, pulmonary congestion and inflammation. Irritant receptors are responsible for deep augmented breaths or sighs seen every 5 - 20 minutes at rest, which reverse the slow collapse of the lungs that occurs in quiet breathing.

Various types of lung receptors provide feedback from the lungs to the respiratory centre.

Stretch Receptors

Stretch receptors are located in smooth muscle of the bronchial walls. Their afferent nerves ascend via the vagus nerve. Stimulation of stretch receptors causes short, shallow breaths, and delay of the next inspiratory cycle. These receptors are largely responsible for the Hering-Breuer reflex where excessive lung inflation inhibits inspiratory muscle activity to prevent over inflation.

Juxtapulmonary (J) Receptors

Juxtapulmonary or 'J' receptors are located on alveolar and bronchial walls close to the capillaries. Their afferents are small unmyelinated C-fibres or myelinated nerves in the vagus nerve. Activation causes depression of somatic and visceral activity by producing apnoea or rapid shallow breathing, a fall in heart rate and blood pressure, laryngeal constriction and relaxation of skeletal muscles via spinal neurones. J receptors are stimulated by increased alveolar wall fluid, pulmonary congestion and oedema, microembolism and inflammatory mediators. J receptors are thought to be involved in the sensation of dyspnoea in lung disease.

Irritant Receptors

Irritant receptors are located throughout airways between epithelial cells, with rapidly adapting afferent myelinated fibres in the vagus nerve. Receptors in the trachea lead to cough, those in the lower airway to hyperpnoea. Stimulation also causes reflex bronchial and laryngeal constriction. Irritant receptors are stimulated by irritant gases, smoke and dust, rapid inflation/deflation, airway deformation, pulmonary congestion and inflammation. Irritant receptors are responsible for deep augmented breaths or sighs seen every 5 - 20 minutes at rest, which reverse the slow collapse of the lungs that occurs in quiet breathing.

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  • Biochemistry
  • Blood Gases
  • Haematology
Biochemistry Normal Value
Sodium 135 – 145 mmol/l
Potassium 3.0 – 4.5 mmol/l
Urea 2.5 – 7.5 mmol/l
Glucose 3.5 – 5.0 mmol/l
Creatinine 35 – 135 μmol/l
Alanine Aminotransferase (ALT) 5 – 35 U/l
Gamma-glutamyl Transferase (GGT) < 65 U/l
Alkaline Phosphatase (ALP) 30 – 135 U/l
Aspartate Aminotransferase (AST) < 40 U/l
Total Protein 60 – 80 g/l
Albumin 35 – 50 g/l
Globulin 2.4 – 3.5 g/dl
Amylase < 70 U/l
Total Bilirubin 3 – 17 μmol/l
Calcium 2.1 – 2.5 mmol/l
Chloride 95 – 105 mmol/l
Phosphate 0.8 – 1.4 mmol/l
Haematology Normal Value
Haemoglobin 11.5 – 16.6 g/dl
White Blood Cells 4.0 – 11.0 x 109/l
Platelets 150 – 450 x 109/l
MCV 80 – 96 fl
MCHC 32 – 36 g/dl
Neutrophils 2.0 – 7.5 x 109/l
Lymphocytes 1.5 – 4.0 x 109/l
Monocytes 0.3 – 1.0 x 109/l
Eosinophils 0.1 – 0.5 x 109/l
Basophils < 0.2 x 109/l
Reticulocytes < 2%
Haematocrit 0.35 – 0.49
Red Cell Distribution Width 11 – 15%
Blood Gases Normal Value
pH 7.35 – 7.45
pO2 11 – 14 kPa
pCO2 4.5 – 6.0 kPa
Base Excess -2 – +2 mmol/l
Bicarbonate 24 – 30 mmol/l
Lactate < 2 mmol/l

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