2. Pleura

Question 1

What is the pleura

Answer 1

The pleura (or strictly speaking the pleurae, as there are two), is the serous
membrane that

invests the lungs as the visceral pleura,
and lines the thoracic cavity as the parietal pleura.

They extend from the dome of the pleura superiorly, to the
diaphragm inferiorly.

The pleural membranes of the left and right lungs do not
connect with each other, being separated by the mediastinum.

Question 2

Parietal pleura:

Answer 2

Parietal pleura: this is continuous but for descriptive purposes is divided into
separate parts. These are the cupola (cervical pleura), the costal pleura, the mediastinal
pleura and the diaphragmatic pleura

Question 3

Visceral pleura

Answer 3

Visceral pleura. The parietal pleura is reflected onto the lung, at which point it
becomes the visceral pleura. It covers the entire surface of the lung, including the
fissures which separate the lobes.

Question 4

Pleural space.

Answer 4

Pleural space.

This is a potential space between the layers of the visceral and parietal
pleura which contains around 10–20 ml of pleural fluid

(it has been calculated as being 0.3 ml kg–1 body weight).

This is produced by the serous membrane and is
similar in composition to plasma apart from its much lower protein count.

It allows movement between the chest wall and the lung.

Question 5

Innervation

Answer 5

Innervation: the visceral pleura receives autonomic innervation via the pulmonary
plexus and like the visceral peritoneum is sensitive to stretch but not to pain or
temperature.

The parietal pleura is innervated by the intercostal nerves and by some
branches of the phrenic nerve, which means that pain can be referred to the
ipsilateral shoulder

Question 6

Vascular supply:

Answer 6

Vascular supply: the visceral pleurae as well as the parenchyma of the lung are
supplied by the internal thoracic arteries.

The parietal pleurae are supplied by the
intercostal arteries. There is rich lymphatic drainage.

Question 7

Pneumothorax.

Answer 7

pleura is vulnerable to damage from amongst other things
trauma, infection and malignancy. There are a number of anaesthetic procedures
that can also put it potentially at risk

Question 8

Pleural effusion.

Answer 8

Pleural effusion.

The small volume of fluid in the pleural cavity is maintained by the

balance of oncotic and hydrostatic pressure
and by efficient lymphatic drainage.

Increases in the normal volume of pleural fluid are always abnormal,

and effusions are classified traditionally as

transudative (low protein)

exudative (high protein

Question 9

Transudative effusions

Answer 9

Causes include
congestive cardiac failure,
hypoproteinaemia,
cirrhosis of the liver
(ascites can cross the diaphragm into the pleural cavity)
and the nephrotic syndrome.

These are essentially ultrafiltrates produced by alterations in the
balance between the oncotic and hydrostatic pressures.

Question 10

Exudative effusions

Answer 10

Exudative effusions:

these are associated with inflammatory pathologies

that include infection,

primary and secondary malignancy
(mesothelioma being the classic tumour of the pleural mesothelial cells)

and autoimmune conditions such as rheumatoid arthritis.

There may be increased capillary disruption,
impaired lymphatic drainage
and increased fluid production
by the pleural membranes themselves.

Exudative effusions can also occur after pulmonary embolism. (As a practical point, it requires
the accumulation of 250 ml of fluid before an effusion is apparent on a chest X-ray