within the rib (or thoracic) cage between the superior thoracic aperture and inferior thoracic aperture.
It contains the mediastinum, pericardial & pleural cavities, and associated organs (heart, lungs, esophagus, trachea) and neurovascular structures (e.g., vagus n., phrenic n., sympathetic chain ganglia, aorta, great vessels).
Inferiorly, the thoracic cavity is separated from the abdominopelvic cavity by the diaphragm.
thoracic cavity contentsa
within 3 serous membrane-lined cavities, the lungs, mediastinum, and associated organs and neurovascular structures.
inferior thoracic aperature (thoracic outlet)
formed by the rib margin, xiphoid process, 11th & 12th ribs, and T12.
It is closed off by the diaphragm.
Clinical Note: Clinically, the superior thoracic aperture is called the �thoracic outlet.�
Sternum and Sternal Angle
The sternum is comprised of three bones: the manubrium, the body, and the xiphoid process.
The manubrium comes together with the body at an angle. This is called �the sternal angle.�
Note that rib 2 articulates at the sternal angle. A
lso note that the heart lies directly behind the body of the sternum.
Ribs & Costal Cartilages
There are 12 pairs of ribs.
The first 7 ribs are true ribs and articulate with the sternum via their own costal cartilage.
Ribs 8-10 are �false ribs� because they do not articulate directly with the sternum but instead they join the costal cartilage of the rib above them.
Ribs 11-12 are �floating ribs� and do not articulate with the sternum.
Ribs are long bones and every long bone has a head, neck, and body or shaft.
The head articulates with the demifacets on vertebral bodies.
The articular facet (see here) articulates with a corresponding costal facet on the transverse processes of vertebrae.
The costal groove accomodates the intercostal nerve and vessels.
The superior and inferior articular processes join two vertebrae together to form the zygapophyseal or facet joints.
The demifacets on the vertebral body and the facets on the transverse process are for the head and articular facets of ribs in the formation of the costovertebral joints.
The ribs articulate with the vertebrae and form costo-vertebral joints.
There is a joint between the head of a rib and vertebral bodies.
There is another joint between the rib and the transverse processes of the vertebrae. They are are synovial joints (subtype: plane or gliding joints). Remember, synovial joints are one of the 3 basic kinds of joints in the body. They have a fibrous joint capsule, synovial membrane, synovial fluid, and hyaline cartilage on the articulating surfaces.
3 muscular layers
From superficial to deep, these layers are formed by:
(1) the external intercostal ms.,
(2) the internal intercostal ms., and
(3) the innermost intercostal ms.
These muscles are located in the intercostal spaces (between ribs) and are supplied by the intercostal nerves and arteries & veins which run between the 2nd and 3rd muscle layers inferior to each rib in the costal grooves.
The intercostal muscles function during inspiration and expiration. However, the diaphragm is the main muscle of respiration.
External & Internal Intercostal Muscles
The external intercostal m. fibers are oriented in a �hands down� position (as if you are putting your hands in your pocket). The internal intercostal m. fibers are oriented in a �hands up� position.
Innermost Intecostal Muscles
lie deep to the internal intercostal layer.
The innermost intercostal layer of muscles can be represented/visualized by the transversus thoracis muscle.
Running between the internal and innermost intercostal muscle layers are the intercostal arteries (and intercostal veins).
The posterior intercostal arteries come from the aorta.
The anterior intercostal arteries come from the internal thoracic arteries.
The posterior and anterior intercostal arteries anastomose together.
Internal Thoracic Arteries
internal thoracic artery originates from the subclavian artery.
ccompanied by the internal thoracic vein which drains into the subclavian vein.
run on each side of the sternum on the internal surface of the thoracic wall.
Also running between the internal and innermost intercostal muscle layers are the intercostal nerves.
ventral rami of spinal nerves from the thoracic segments of the spinal cord
innervate the intercostal muscles.
(Vein, Artery, Nerve) Relationship
Posteriorly, the intercostal vein, artery, and nerve travel in the middle of each intercostal space.
Laterally and anteriorly along the thoracic wall (depicted here), they run in the costal groove of the superior rib.
From superior to inferior, the relationship is vein, artery, and nerve (VAN).
These structures run between the internal and innermost intercostal muscle layers.
The Pleural Cavities
2 separate serous-membrane lined cavities related to each lung
Each pleural cavity is lined by a serous membrane which forms an enclosed sac which normally contains a thin layer of serous fluid.
The lungs are not in the pleural cavities, but are outside of them.
The serous membrane of each cavity is called �the pleura.�
Imagine that the developing lung is like �fist�.
As it develops it presses against the outside of the balloon until it becomes covered by �balloon tissue�.
The fist is still not inside the balloon itself.
The pleural cavity is like the balloon and the lung is like the fist which pushes against it thus becoming covered by pleura but still not being in the pleural cavity.
Remember, there is nothing in the pleural cavity normally except a thin layer of serous fluid.
can be divided into two �kinds�. It is really all one continuous membrane.
However, there is some pleura intimately covering the lung which is an organ and so we can call this the visceral pleura.
The rest of the pleura projects along the walls of the pleural cavity and so it is called parietal pleura (parietum means �wall� in latin).
These two pleura are continuous around the root of the lung.
The pleural cavity is that space between the visceral and parietal pleura.
divided up into
cervical (relating to the neck, it is also called �apical� or �the cupola�)
diaphragmatic parietal pleura.
It is still all one continuous membrane.
However, this additional vocabulary helps us talk about the parietal pleura in its different locations.
Within each pleural cavity are special areas where the parietal pleura extends beyond the borders of the lung.
These are called pleural recesses.
There are two such recesses: the costomediastinal recess and the costodiaphragmatic recess.
These recesses function to allow expansion of the lung during heavy breathing.
Lung & Pleura Borders (using Rib Landmarks)
allow us to see how the pleura (and the costodiaphragmatic recess) extend beyond the lungs.
Lungs CD recess
Midclavicular line rib 6 rib 8
Midaxillary line rib 8 rib 10
Midscapular line rib 10 rib 12
primary organs of respiration
attached to the heart and trachea by structures in the roots of the lungs.
root of the lung includes structures which enter and leave the lung such as the pulmonary vessels, main bronchus, bronchial vessels, lymph vessels, and nerves (the pulmonary plexus).
right lung has 3 lobes
left lung has 2 lobes.
These lobes are not the functional units of the lungs.
The functional units of the lungs are the bronchopulmonary segments.
Each lung has a costal surface (related to the ribs), diaphragmatic surface (related to the diaphragm), and a mediastinal surface (related to the mediastinum).
Lung Apex & Base
Each lung also has an apex and a base.
The base is the same as the diaphragmatic surface.
Each lung also has a sharp anterior margin and a blunt posterior margin.
You can use the apex (which is superior) and the sharp anterior margin to orient yourself so that you can tell whether you are looking at a right or left lung.
The right lung has two fissures: a horizontal fissure and oblique fissures.
The left lung has one fissure: an oblique fissure. The cardiac incisure and lingula are features of the left lung.
The right lung has 3 lobes - a superior, middle, and inferior lobe.
The left lung has 2 lobes - a superior and inferior lobe.
However, these morphological lobes are not the functional units of the lung.
The true functional units of the lung are the broncho-pulmonary segments.
These segments are defined as portions of the lung that have their own tertiary (or segmental) bronchus.
The trachea bifurcates into the primary or main bronchi. Each main bronchus divides into secondary bronchi.
The secondary bronchi divides into tertiary or segmental bronchi - which define the bronchopulmonary segments.
Right Lung Impressions
The relationships of the right lung to other organs are indicated by the impressions that those organs make on its hilar surface.
Note the positions of the grooves for the azygos vein, superior vena cava, and esophagus.
Also note the cardiac impression.
Left Lung Impressions
The relationships of the left lung to other organs are indicated by the impressions on its hilar surface.
Note the grooves for the aortic arch, descending aorta, and the larger cardiac impression.
Root of the Lung
includes those structures that enter or leave the lungs.
These structures include the pulmonary artery, pulmonary vein, primary bronchus, pulmonary nerve plexus, lymphatics, and the bronchial artery and vein.
Blood Supply to the Lungs
by way of the bronchial arteries which originate from the aorta (some variations are depicted here).
These arteries actually supply blood to the lung tissue itself and are part of the root of the lung structures.
The lungs are innervated by the pulmonary plexus which is a visceral nerve plexus consisting of visceral efferent (VE) fibers of the ANS and visceral afferent (VA) fibers.
The VE fibers include parasympathetic preganglionic (para/pre) fibers from the vagus nerve (CN X) and sympathetic postganglionic (symp/post) fibers from the sympathetic trunk.
To summarize, the pulmonary plexus has the following functional components: VA, VE-para/pre, VE-symp/post.
The pulmonary plexus fibers enter into the root of the lung.
The main muscle of respiration is the diaphragm.
When it contracts, it moves inferiorly increasing the vertical dimension of the thorax.
When the intercostal muscles contract, both the transverse (the bucket-handle action) and anteroposterior (the pump-handle action) diameters of the thorax increase.
This 3-dimensional increase in thorax dimensions results in inspiration as air moves from higher pressure to lower pressure.
Elastic recoil of the lung tissue results in expiration.
When the diaphragm contracts, it increases the vertical dimension of the thorax.
The diaphragm is a striated, voluntary (somatic) muscle.
The diaphragm is innervated by the phrenic nerve which is a somatic nerve formed by fibers from the C3,4,5 spinal cord levels. (Remember: �C3,4,5 keeps the diaphragm alive�).
The diaphragm attaches to the xiphoid process (sternum), upper lumbar vertebrae, and inferior margin of the thoracic cage.
Contraction of the intercostal muscles results in two inspiratory movements of the thorax:
the bucket-handle action and the pump-handle action. The bucket-handle action (depicted here) results in an increase in the transverse dimension of the thorax.
Contraction of the intercostal muscles results in two inspiratory movements of the thorax: the bucket-handle action and the pump-handle action.
The pump-handle action (depicted here) results in an increase in the antero-posterior dimension of the thorax.