Anatomy
Thorax
Regarding the pleura, which of the following statements is CORRECT:
Answer:
Superiorly, the pleural cavity projects as much as 3 - 4 cm above the first costal cartilage but does not extend above the neck of rib 1. The two pleurae approach each other medially but are separated by the middle mediastinum. The costal pleura (the part of the parietal pleura related to the ribs and intercostal spaces) is innervated by the intercostal nerves. The lungs do not completely fill the pleural cavities, producing two pleural recesses, the costomediastinal and costodiaphragmatic recesses, in which fluids can collect.Pleura
Anatomy / Thorax / Pleura and Lungs
Last Updated: 11th April 2019
Each lung is surrounded by a pleura. The pleura consists of two parts, the parietal pleura (which lines the thoracic cavity) and the visceral pleura (which lines the lungs). The two parts of the pleura are continuous with each other at the hilum of each lung. The potential space between these two parts of the pleura is called the pleural cavity.
Pleural Cavity. (Image by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)
Pleural Cavity
The pleural cavity normally contains a small amount of lubricating fluid to allow the visceral pleura attached to the lungs to smoothly slide over the parietal pleura attached to the thoracic wall during respiration. The serous fluid also produces a surface tension, pulling the parietal and visceral pleura together. This ensures that when the thorax expands, the lung also expands, filling with air.
Innervation
The parietal pleura is innervated by somatic afferent fibres. The costal pleura (pleura related to the ribs and intercostal spaces) is innervated by branches of the intercostal nerves, and pain is felt in relation to the thoracic wall. The diaphragmatic pleura (covering the diaphragm) and the mediastinal pleura (covering the mediastinum) are innervated mainly by the phrenic nerves (C3 - C5), and pain is referred the the C3 - C5 dermatomes (lateral neck and supraclavicular region of shoulder).
Although the visceral pleura is innervated by visceral afferent fibres, pain is not generally elicited from this tissue.
Surface Markings
Superiorly the pleural cavity projects as much as 3 - 4 cm above the first costal cartilage but does not extend above the neck of rib 1.
Anteriorly the pleurae approach each other posterior to the upper part of the sternum. At the lower part of the sternum the left pleura does not come as close to the midline as the right pleura because the middle mediastinum bulges to the left.
Inferiorly the pleura reflects onto the diaphragm above the costal margin. The inferior margin of the pleural cavity is a line that runs between rib 8 in the midclavicular line, rib 10 in the midaxillary line and vertebra T12 posteriorly.
The inferior margin of the lung in quiet respiration is a line that runs between rib 6 in the midclavicular line, rib 8 in the midaxillary line and vertebra T10 posteriorly.
The lungs therefore do not completely fill the pleural cavities, producing two pleural recesses, the costomediastinal and costodiaphragmatic recesses, in which fluids can collect.
The costomediastinal recess occurs on each side where the the costal pleura is opposed to mediastinal pleura, particularly on the left side in the region overlying the heart.
The costodiaphragmatic recess occurs between the costal and diaphragmatic pleura. It is the region between the inferior margin of the lung and the inferior margin of the pleural cavity and is clinically important for pleural aspiration.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Lung-pleura.png)
Surface Markings of the Pleura. (Image by Henry Vandyke Carter [Public domain], via 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 |
