Thorax

The pleura

The pleura


General arrangement of thoracic cavity Development of the lung Parts of parietal pleura Pulmonary ligament Surface projection of the pleura Pleural recesses Nerve supply Blood supply Pneumothorax Pleural effusion

General arrangement of the thoracic cavity

In a cross section through the chest you will find that the thoracic cavity contains principally two pleural cavities with, between them, the mediastinum

General arrangement of the thoracic cavity

the aorta lies in contact with the vertebral bodies slightly to the left of the midline producing slight flattening of the left side of the thoracic vertebral bodies of the middle of the series

General arrangement of the thoracic cavity

The esophagus lies anterior to the aorta

General arrangement of the thoracic cavity

the trachea is not shown since the section passes at a level below the level of the sternal angle where the trachea bifurcates

General arrangement of the thoracic cavity

The posterior border of the lung is rounded because it is shaped by the ribs. The anterior border is sharp because it fits in between the heart and the chest. From the front, therefore, part of the heart is in contact with the chest wall but part of it is overlaid by lung tissue

General arrangement of the thoracic cavity

The mediastinum forms a complete septum across the chest from front to back so that change in pressure in one pleural cavity may deflect the mediastinum to one side


The clinician can recognize mediastinal deviation by feeling the position of the trachea at the root of the neck where the trachea can normally be felt most anteriorly in the midline at the jugular notch

Hilum and root of the lung

The hilum of the lung is the site where structures like bronchi, pulmonary vessels, and others enter or leave the lung. These structures together contribute what is called the root of the lung, which connects the lung to the mediastinum

Pleural cavity

The pleural cavity on each side is almost completely filled by a lung, leaving a the cavity as a potential space containing a thin film of fluid (pleural fluid). The pleura is a thin membrane of fibrous tissue surfaced by a single layer of flat cells to make it slippery

Layers of pleura

The pleura is in two layers, the visceral pleura which covers the outer surface of the lung and is continuous at the hilum with the parietal pleura that lines the thoracic cavity on each side of the mediastinum

Visceral pleura

Unlike the parietal pleura, the visceral pleura dips into the lung fissures; therefore, in the fissures, the visceral pleura of adjacent lobes lie in contact with each other.

Development of the lung

each lung develops from a lung bud from what is called the laryngotracheal tube

Development of the lung

Each lung bud invaginates the wall of the celomic cavity

Development of the lung

Each lung then grows to fill the greater part of the cavity so that the original celomic cavity is reduced to a slit‑like space called the pleural cavity

Development of the lung

The lung will be covered with splanchnic mesoderm that forms the visceral pleura, while the thoracic wall will be lined by parietal pleura. This also demonstrates how the two layers of pleura are continuous with each other at the root of the lung

Parts of parietal pleura

The parietal pleura, though a continuous sheet, is given different names according to the parts it covers. It is therefore divided into costal, mediastinal, diaphragmatic, and cervical pleura

Costal pleura

The costal pleura covers the internal surfaces of the sternum, costal cartilages, ribs, intercostal muscles and the sides of thoracic vertebrae, separated from all these structures by a thin layer of loose connective tissue called the endothoracic fascia

Mediastinal pleura

The mediastinal pleura covers the mediastinum, it is continuous anteriorly and posteriorly with the costal pleura

Diaphragmatic pleura

Inferiorly, the mediastinal pleura is continues with the diaphragmatic pleura that covers the superior surface of the diaphragm while superiorly it is continuous with the cervical pleura

Pulmonary ligament

At the root of the lung, the mediastinal pleura passes laterally forming a sleeve that encloses the structures at the lung root

Pulmonary ligament

Inferior to the lung root the sleeve of the mediastinal pleura is too big for the contained structures forming a double layer called the pulmonary ligament

Pulmonary ligament

If you pinch together the cuffs of a jacket below your wrist, you will understand how the lower part of the sleeve at the hilum forms a double layer i.e. the pulmonary ligament

Pulmonary ligament

The pulmonary ligament is an ill‑chosen name (a misnomer), it has nothing to do with the lung since it is pleura; in addition, the pulmonary ligament is not a ligament in the correct sense of the meaning, it is a double fold of pleura that hangs down below the lung root as an empty fold

Function of the pulmonary ligament

The function of the pulmonary ligament is to provide a dead space into which the lung root descends with descent of the diaphragm.

Function of the pulmonary ligament

More important is that pulmonary veins (contained in the lung root) can expand during periods of increased venous return from the lungs as in exercise (remember that the pulmonary veins carry oxygenated blood from the lungs to the heart)

Function of the pulmonary ligament

It is interesting to note that the two pulmonary veins at each root lie at the lower part of the root just above the pulmonary ligament


At the lung hilum the uppermost structure is the pulmonary artery (artery above) while the main bronchus is situated more posteriorly (bronchus behind). In front and below are the pulmonary veins

The femoral vein is related medially to the femoral canal, a potential space

You will notice that in many regions of the body, large veins always have a dead space nearby to allow for their dilation during times of increased venous return. Veins can dilate since they consist of thin wall unlike the arteries

Cervical pleura

The cervical pleura or the cupola of the pleura extends through the superior thoracic aperture into the root of the neck.

Cervical pleura

Its summit is 2‑4 cm superior to the medial 1/3rd of the clavicle

Cervical pleura

The cervical pleura does not extend superior to the neck of the first rib because the first rib slopes inferiorly.

Cervical pleura

Extension of the lung and pleura into the root of the neck make them liable to be injured in wounds of the neck

Surface projection of the pleura

Think of even numbers. The cervical pleura extends into the neck 2-4cm above the medial third of the clavicle

Surface projection of the pleura

From this point, the pleura passes behind the sternoclavicular joint reaching the midline at the level of the 2nd costal cartilage.

Surface projection of the pleura

From here, the two pleural cavities are in contact as far as the 4th cartilage, here the right pleura continues vertically down to the level of the 6th costal cartilage

Surface projection of the pleura

Here the right pleura continues vertically down to the level of the 6th costal cartilage

Surface projection of the pleura

The left pleura arches laterally at the level of the 4th costal cartilage and descends lateral to the border of the sternum down to the level of the 6th costal cartilage

Surface projection of the pleura

At the level of the 6th costal cartilage the pleura on both sides pass around the chest wall crossing the 8th rib at the mid‑clavicular line

Surface projection of the pleura

The pleura on both sides pass around the chest wall crossing the 10th rib at the mid-axillary line

Surface projection of the pleura

The pleura on both sides pass around the chest wall crossing the 12th rib at the back

Pleural reflections

The previously-mentioned lines are called lines of pleural reflection. The sternal pleural reflection is where the costal pleura is continuous with the mediastinal pleura posterior to the sternum.

Pleural reflections

The costal pleural reflection is where the costal pleura is continuous with the diaphragmatic pleura near the costal margin

Pleural reflections

The vertebral reflection lies posteriorly along the lateral side of the bodies of thoracic vertebrae.

Pleural reflections

The mediastino‑diaphragmatic reflection connects the inferior ends of the sternal and vertebral reflections


The lung markings correspond to those of the pleura above but are two ribs higher in the lower part of the thorax.


Thus the lung reaches the level of the 6th costal cartilage or rib in the mid‑clavicular line, 8th rib in the mid‑axillary line

The lung reaches the level of the 10th rib posteriorly

Pleural recesses


During full inspiration, the lung expands and fill the pleural cavity; but during quiet inspiration there are three sites where the lung does not fully occupy the pleural cavities.

Pleural recesses

At these sites the two layers of parietal pleura are in contact with each other at their inner surfaces. The sites where parietal pleura comes into contact with parietal pleura are called pleural recesses

Pleural recesses

The pleural recesses are only occupied by lung tissue during full inspiration, they are the right and left costo-diaphragmatic recesses and the costo-mediastinal recess

Costodiaphragmatic recess

Is located at the inferior margin of the pleura

Costodiaphragmatic recess

Radiologists call this region the costophrenic angle.

Costodiaphragmatic recess

Excess fluid in the pleural cavity will cause an opacity which obliterates the angle

Costo-mediatinal recess

Lies along the anterior margin of the pleura where the costal angle and mediastinal parts of the left pleura come into contact at the cardiac notch in the anterior border of the left lung where it overlies the heart.


4
5

Costo-mediatinal recess

Lies at the anterior ends of the 4th and 5th intercostal spaces and during full inspiration it becomes occupied by the lingula of the left lung


The pleura descends inferior to the costal margin in three regions 1- the right infrasternal angle

2 & 3:The right and left costovertebral angles.

These regions should be remembered by the surgeon when making incisions through the anterior abdominal wall so that the incision should not enter the pleural sac since this results in pneumothorax.



This is especially important for the costo-vertebral angles Which are located behind the upper pole of the kidney and are liable to be opened while incising for nephrectomy (removal of the kidney)

Nerve supply

The visceral pleura should be regarded as part of the lung, the parietal pleura as part of the chest wall.

Nerve supply

The nerve supply of the visceral pleura as in the lung is autonomic through nerves that accompany the bronchial arteries, these are vasomotor. The visceral pleura is thus insensitive to ordinary stimuli as pain and touch.

Nerve supply

The parietal pleura as part of the chest wall is supplied by somatic nerves namely intercostal and phrenic nerves.

Nerve supply

The collateral branches of intercostal nerves segmentally supply the costal pleura and the peripheral part of the diaphragmatic pleura

Nerve supply

The central part of the diaphragmatic pleura and the mediastinal pleura are supplied by the phrenic nerves. The parietal pleura is thus sensitive to pain.

Refered pleural pain

Irritation of the costal and peripheral part of the diaphragmatic pleura by disease causes local pain and referred pain i.e. pain referred or seems to be arising frown regions supplied by the same intercostal nerves that supply the pleura. Thus pain is referred to the chest and abdominal walls, both are supplied by intercostal nerves

Refered pleural pain

Irritation of the mediastinal or central part of the diaphragmatic pleura supplied by the phrenic nerve is referred to the tip of the shoulder where the dermatome there is that of C4 since the root value of the phrenic nerve is C3, 4, and 5 mainly C4


Irritation of the parietal peritoneum below the diaphragm (which is also supplied by the phrenic nerve) is also referred to the tip of the shoulder


therefore pain is referred to the dermatome whose root value is the same as that of the phrenic nerve. A root value of a nerve is the spinal cord segment from which it is derived

Blood supply

The visceral pleura derives its arterial supply froth bronchial arteries that supply lung tissue with oxygenated blood

Blood supply

The bronchial arteries are branches of the thoracic aorta.

Intercostal vessels

Blood supply


The blood supply of the parietal pleura is derived from that supplying the chest wall namely internal thoracic, intercostal, and musculophrenic arteries


The pleural cavity is a potential space containing a thin film of pleural fluid The pressure inside the cavity is slightly below atmospheric The pressure inside the lung is more or less atmospheric.

Pneumothorax

If the chest wall is penetrated following for example a stab wound or the visceral pleura is punctured usually as a result of rupture of bullae on the surface of the lung, air enters the pleural cavity so that its pressure becoming the same as that inside the lung; since the lungs are more elastic, the lungs tend to collapse

Tension pneumothorax

Sometimes air enters the pleural cavity during inspiration

Tension pneumothorax


But air cannot leave during expiration causing an increased accumulation of air (positive pressure pneumothorax).

Tension pneumothorax

This is dangerous since air accumulation will not only compress the ipsilateral lung but it will push the mediastinum to the other side compressing the opposite lung and killing the patient

Pleural effusion (hydrothorax)

The presence of excess fluid in the pleural cavity The fluid tends to gravitate towards the costomediastinal recesses, thus, it obliterates the costophrenic angle.

Pleural effusion (hydrothorax)

Accumulation of more fluid, like in pneumothorax, tends to collapse the lung and displace the mediastinum to the other side