Physiology
Respiratory
Which of the following is part of respiratory host defence:
Answer:
Macrophages in the airways ingest foreign materials and destroy pathogens. In the alveoli, alveolar macrophages take the place of cilia by clearing debris. Surfactant is produced by type II pneumocytes. The mucociliary escalator only extends down to the respiratory bronchioles and does not extend into the alveolar epithelium. The respiratory tract contains a predominance of IgA immunoglobulin. Alpha-1-antitrypsin is an anti-protease that protects the airway from destructive proteases released by pathogens and immune cells.Respiratory Epithelial Function
Physiology / Respiratory / Lung Mechanics
Last Updated: 30th March 2020
Mucociliary Clearance
The respiratory tract from the trachea down until the respiratory bronchioles is lined with ciliated columnar epithelial cells. Goblet cells and submucosal glands secrete a thick, gel-like mucus. Synchronous beating of the cilia moves the mucus and associated debris to the mouth where it is swallowed or expectorated, a process known as mucociliary clearance.
Impaired Mucociliary Clearance
Factors that increase the viscosity of the mucus (e.g. cystic fibrosis, asthma, inflammation or poor humidity) or factors that impair ciliary activity (e.g. smoking, pollutants, infection or general anaesthetics) lead to defective mucociliary clearance and recurrent infections.
Mucus contains substances that protect the airway from pathogens and from destructive proteases released from dead bacteria and immune cells e.g. alpha-1-antitrypsin, lysozyme, IgA. Genetic deficiency of alpha-1-antitrypsin leads to early-onset emphysema as a result of uninhibited protease activity in the lung resulting in destruction of elastin in the alveoli.
Epithelial Cells
The single layer of epithelial cells forming the walls of the alveoli and alveolar ducts are non ciliated squamous cells, predominantly very thin type I alveolar pneumocytes joined by tight junctions lying on a basement membrane. These form the gas exchange surface with the pulmonary capillary endothelium.
A few type II alveolar pneumocytes make up a small proportion of the alveolar surface area and secrete surfactant which bathes the alveoli, reducing the surface tension and preventing alveolar collapse.
Macrophages in the airways ingest foreign materials and destroy pathogens. In the alveoli, alveolar macrophages take the place of cilia by clearing debris.
Structure of an Alveolus. (Image modified by FRCEM Success. Original sourced from Wikimedia Commons.)
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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 |
