Physiology
Respiratory
Which of the following receptors are responsible for the Hering-Breuer reflex preventing overinflation of the lungs:
Answer:
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.Lung Receptors
Physiology / Respiratory / Control of Respiration
Last Updated: 11th April 2019
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 |
