Dr. Mujahid Khan

The pleurae and lungs lie on either side of the mediastinum within the chest cavity

Each pleura has two parts:

Parietal layer Visceral layer

It lines the thoracic wall

Covers the thoracic surface of the diaphragm and the lateral aspect of the mediastinum

Extends into the root of the neck to line the undersurface of the suprapleural membrane at the thoracic outlet

It completely covers the outer surfaces of the lungs

Extends into the depths of the interlobar fissures

The two layers continuous with one another by means of a cuff of pleura

This cuff surrounds the structures entering and leaving the lung at the hilum of each lung

Pleural cuff hangs down as a loose fold called the pulmonary ligament

The parietal and visceral layers are separated from one another by a slitlike space called pleural cavity

Clinicians use the term pleural space instead of the anatomic term pleural cavity

Pleural cavity contains thin film of tissue fluid called pleural fluid

Fluid permits the two layers to move on each other with the minimum of friction

Parietal pleura is divided into the region in which it lies or the surface that it covers

The cervical pleura extends up into the neck

It lines the undersurface of the suprapleural membrane

It reaches a level 1 to 1.5 in. (2.5 to 4 cm) above the medial third of the clavicle

It lines the inner surfaces of:

The ribs The costal cartilages The intercostal spaces The sides of the vertebral bodies The back of the sternum

It covers the thoracic surface of the diaphragm

In quiet respiration, the costal and diaphragmatic pleurae are in apposition to each other below the lower border of the lung

Costal and diaphragmatic pleurae separate in deep inspiration

The lower area of the pleural cavity into which the lung expands on inspiration is referred to as the costodiaphragmatic recess

It covers and forms the lateral boundary of the mediastinum

It is reflected as a cuff around the vessels and bronchi at the hilum of the lung

Then continuous with the visceral pleura

Each lung lies free except at the hilum

it is attached to the blood vessels and bronchi that constitute the lung root

During full inspiration the lungs expand and fill the pleural cavities

During quiet inspiration the lungs do not fully occupy the pleural cavities at four sites

The right and left costodiaphragmatic recesses

The right and left costomediastinal recesses

Are slitlike spaces between the costal and diaphragmatic parietal pleurae

Separated only by a capillary layer of pleural fluid

During inspiration, the lower margins of the lungs descend into the recesses

During expiration, the lower margins of the lungs ascend so that the costal and diaphragmatic pleurae come together again

Are situated along the anterior margins of the pleura

They are slitlike spaces between the costal and the mediastinal parietal pleurae

Separated by a capillary layer of pleural fluid

During inspiration and expiration, the anterior borders of the lungs slide in and out of the recesses

The parietal pleura is sensitive to pain, temperature, touch and pressure, and is supplied as follows:

The costal pleura is segmentally supplied by the intercostal nerves

The mediastinal pleura is supplied by the phrenic nerve

The diaphragmatic pleura is supplied over the domes by the phrenic nerve and around the periphery by the lower six intercostal nerves

The visceral pleura covering the lungs is sensitive to stretch

It is insensitive to common sensations such as pain and touch

It receives an autonomic nerve supply from the pulmonary plexus

The pleural space normally contains 5 to 10 ml of clear fluid

It lubricates the opposing surfaces of the visceral and parietal pleurae during respiration

The formation of the fluid results from hydrostatic and osmotic pressures between the capillaries

The pleural fluid is normally absorbed into the capillaries of the visceral pleura

Any condition that increases the production of the fluid or impairs the drainage of the fluid results in the abnormal accumulation of fluid, called pleural effusion

The presence of 300 ml of fluid in the costodiaphragmatic recess in an adult is sufficient to enable its clinical detection

The clinical signs include decreased lung expansion on the side of the effusion, with decreased breath sounds and dullness on percussion over the effusion

Inflammation of the pleura secondary to inflammation of the lung called pneumonia

Pleural surfaces become coated with inflammatory exudate, causing the surfaces to be roughened

Produces friction, and a pleural rub

It can be heard with the stethoscope on inspiration and expiration

Often the exudate becomes invaded by fibroblasts

That lay down collagen and bind the visceral pleura to the parietal pleura

Forms pleural adhesions