Physiology
Respiratory
The walls of the alveoli are predominantly formed by:
Answer:
The single layer of epithelial cells forming the walls of the alveoli and alveolar ducts are nonciliated 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.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.)
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- 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 |
