Learning Objectives for Blood on the Road
How are the lung and the chest wall related?
Definitions:
Chest wall: thoracic wall
The true thoracic wall includes the thoracic cage and the muscles that extend
between the ribs as well as the skin and cutaneous tissue, muscles, and fascia
covering it's anteriolateral aspect.
Thoracic wall contains the thoracic cavity, consisting of:
-
-
Right and left pulmonary cavities: non communicating (non-connected)
cavities containing:
o Lungs
o Pleurae
Central mediastinum (media=layer,
stinum= ??), a compartment
separating the pulmonary cavities.
It contains:
o Heart
o 'Great' Vessels (vena cava,
aorta)
o Trachea,
o Oesophagus
o Thymus
o Lymphatic structures
The lungs are the chest wall are related via the pleurae, a serous sac (serum
producing sac) consisting of:
-
Visceral Pleura: engulfs all surfaces of the lungs
Parietal Pleura: lines pulmonary cavities, consisting of:
o costal part
o mediastinal part
o diaphragmatic part
o cervical part: extends to line of C7 vertebrae
The pleural 'space' is a layer of serous/'serum-like' pleural fluid. The
lubrication of this fluid produces the ideal low-resistance environment needed to
facilitate efficient respiration. It also creates the surface tension needed for the
lungs to adhere to the chest/thoracic wall
From which structures could blood loss and air leaks arise?
Air leaks can come from:
-
Lung itself
External environment
This can be due to a penetrating injury to the thoracic cage (bullet, knife,
fractured rib), or the rupture of a pulmonary lesion into the pleural cavity
(bronchopulmonary fistula)
Air leaks causing a build up of pressure in the pleural cavity is called a
pneumothorax. This inevitably results in a collapse of the lung. Air in the
pleural cavity appears black on a radiograph, whilst lung tissue consists of
blackened areas with white lung markings
Blood loss could arise from:
-
Pulmonary vessels: especially the pulmonary arteries and veins
Lobar vessels (supply lobes of lungs)
Bronchial vessels
The 'great' vessels: aorta, superior/inferior vena cava
The coronary vessels, and other vessels that supply the heart
The heart itself
Blood leaks causing a build up of pressure within the pleural cavity is called a
haemothorax. They are represented by vast quantities of white on a radiograph suggesting fluid build up. Non-blood fluid build up in the pleura is called a
hydrothroax.
Characteristics of pneumothorax on radiograph:
-
Denser areas of white (collapsed lung) surrounded by blacker air
Elevation of diaphragm above usual level
Narrowed intercostal spaces
Mediastinal shift and tracheal deviation TOWARDS affected side
Which structures prevent the blood and air from moving
out into other tissues?
The pleura and mediastinum prevent the movement of blood and air into other
tissues. Thus, instead of moving to other regions of the body, blood and air can
accumulate within these tissues and place pressure on the vital organs within
them.
Normal lung (below)
Haemopneumothorax (below)
Sources: excuse lazy referencing!
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Clinically oriented anatomy
Google definitions
Wikipedia (pictures)
British Medical Journal (for pictures)