Anatomy of thorax and mediastinum Flashcards
What is the function of the thorax?
Protects the lungs, great vessels, liver and spleen
Provides the mechanical function of breathing
What are the skeletal components of the thoracic wall?
12 thoracic vertebrae
12 pairs of ribs
Sternum (manubrium, body and diploid process)
See figure
Parts of the manubrium and the sternum
Manubrium:
Jugular notch
Clavicular notch
First costal notch
Sternal angle (angle of louis)
Manobriosternal joint
Sternum:
Body
2nd-7th costal notches
Xiphisternal joint
Xiphoid process
What passes to the right and behind the manubrium?
The aortic arch
What does the xiphisternal joint mark?
The centre of the diaphragm
Marks how high the liver goes
Left side of process = inferior border of the heart
What are the two parts of a rib?
Bony part (costo-)
Cartilage part (chondro-)
Where do the 12 pairs of ribs attach posteriorly? Type of joints?
Thoracic vertebrae
Mostly synovial
What is the diameter of the thoracic cage?
Not equal
More narrow superiorly
Parts of typical rib
Head
Neck
Costal tubercule
Costal angle
What do the facets of the head of the rib articulate with?
Two facets are separated by the crest of the head
One facet articulates with the body of the numerically corresponding vertebrae
Other facet articulates with the superior vertebrae
See figure
Role of costal tubercle of typical ribs
Located at the junction of the neck and body.
Has a smooth articular part for articulating with the corresponding transverse process of the vertebra (via a synovial joint)
Rough non-articular part for a fibrous attachment to the process via the costotransverse ligament
See figure
Typical and atypical ribs
Typical: 3-9
What are the true ribs? What joints to they form
aka Vertebrosternal ribs
1st to 7th ribs
attach directly to the sternum anteriorly through their own costal cartilages.
Form sternochondral joints
What are the false ribs?
aka Vertebrochondral ribs
8-10th ribs
cartilages on their anterior ends that are joined to the cartilage of the rib just superior to them
connection with the sternum is indirect.
synchondrosis (immovable joint)
What are the floating ribs?
11th and 12th, sometimes the 10th
Rudimentary cartilages on their anterior ends that do not connect even indirectly with the sternum
instead, they end in the posterior abdominal musculature.
What are the distinguishing features of the 2nd rib
Has formations for attachment of serrates anterior and posterior scalene muscles
What are the costal grooves of the ribs for?
To protect intercostal vessels and nerves
What is the role of the costal cartilage?
Prolong ribs anteriorly
Contribute to the elasticity of the thoracic wall
Thoracic cavity during inspiration
Inspiration: The vertical dimension (height) of the central part of the thoracic cavity increases during as the contracting diaphragm descends
Elevation of sternum causes the anteroposterior (AP) dimension of the thorax to increase considerably (pump-handle movement)
Elevation of the lateral portion of the lower ribs causes the transverse dimension of the thorax to increase (bucket-handle movement)
See figures
Which muscles of the thoracic wall work during inspiration?
Elevation of ribs
Scalenus muscles (forced inspiration)
External intercostal muscles
See figures
Which muscles of the thoracic wall work during forced expiration?
Internal intercostal muscles
Innermost intercostal muscles
Transverse thoracic muscle
Subcostal muscles
See figures
What are the muscles of the thoracic wall innervated by?
Intercostal nerves
What are the scalenus muscles innervated by?
Cervical plexus
What do the scalene muscles attach to?
1st rib: anterior and middle scalene
2nd rib: posterior scalene
Three layers of muscles in the intercostal spaces
outer layer: External intercostals
middle layer: internal intercostal
deepest: innermost intercostals
Orientation of muscle fibres of intercostal muscles?
External: infero-anterior (putting hands in pockets)
Internal: infero-posteriorly
Deepest: similar to internal (internal to the intercostal vasculature)
See figure
What structures form the thoracic inlet?
Thoracic inlet = superior aperture of thorax
First thoracic vertebra, upper margins of first ribs and manubrium of sternum
What structures form the thoracic outlet?
12th thoracic vertebrae behind
11th and 12th ribs on the sides
cartilages of the 10th, 9th, 8th and 7th ribs (ascend on each side and form an angle into the apex)
Outlet slopes obliquely downward and backward
What closes the thoracic outlet?
Diaphragm (forms floor of thorax)
What is the principal muscle of respiration?
Diaphragm
Diaphragm and respiration
Inspiration: diaphragm contracts and flattens. This increases the vertical diameter of the thoracic cavity, producing lung expansion and air is drawn in.
Expiration: diaphragm passively relaxes and returns to its original dome shape. Reduces volume of thoracic cavity
Dome of diaphragm? Need to ask about this
Level of T8 on right side
Level of T9 on left side
Parts of diaphragm
Central tendon: fused with the inferior part of the fibrous pericardium
Sternal part: two muscular slips that attach to posterior aspect of diploid process
Costal part: wide muscular slips that attach to the internal surfaces of the inferior six costal cartilages and their adjoining ribs on each side (forms domes of diaphragm)
Lumbar part
Actions of diaphragm
Principle muscle of respiration
Active part in coughing, forced defecation, weight lifting
Innervation of diaphragm
Phrenic nerve, C3, C4, C5
Keeps the diaphragm alive
3 major openings of the diaphragm
Vena cava aperture (level of T8)
Esophageal aperture (level of T10)
Aortic aperture (level of T12)
See figure
Changes in thoracic volume during inspiration
Inspiratory muscles contract
External intercostals elevate ribs
Diaphragm flattens
-> rib cage rises, increase in thoracic cavity in all of it’s dimensions (anterior-posterior and superior-inferior)
Changes in thoracic volume during expiration
Inspiratory muscles relax
External intercostals relax
Diaphragm rises
-> rib cage descends due to recall of costal cartilages, decrease in thoracic cavity volume
What do the arteries of the thoracic wall derive from?
Thoracic aorta -> posterior intercostal arteries
Subclavian artery -> internal thoracic -> anterior intercostal arteries
See figure
What are the intercostal veins? Branches?
Posterior intercostal -> azygous vein
Anterior intercostal -> internal thoracic vein
Both drain into superior vena cava
See figure
What are the veins of the thoracic wall?
Azygous vein (right)
Accessory Hemiazygous vein
Hemiazygous vein (drains into azygous)
See figure
What do the veins of the thoracic wall drain into?
The superior vena cava
How many pairs of spinal nerves does the thoracic wall have?
12 pairs of spinal nerves
What types of innervation do the nerves of the thoracic wall provide?
Provide motor supply to muscles of thoracic and abdominal wall
Provide sensory supply to skin and costal parts of the diaphragm
Provide sympathetic innervation to the skin (e.g. sweat glands, blood vessels)
What do the ventral rami of the thoracic spinal nerves supply?
The intercostal spaces of the thorax
Which ventral rami form the intercostal nerves? Where do they run?
T1-T11
These nerves run along the extent of the intercostal spaces
See figure
Where is the ventral rami of T12? What is it named?
Inferior to the 12th rib
Subcostal nerve
Where do the dorsal rami of the spinal nerves run? What do they supply?
run posteriorly (clos to vertebrae)
supply bones, joints, muscles and skin of the back region of the thorax
What is a dermatome?
An area of skin supplied by sensory neurons that arise from a spinal nerve ganglion.
Single nerve innervates single dermatome
Which nerves innervate the dermatomes of the thoracic wall?
Sensory branches of intercostal nerves
What is the content of the intercostal spaces?
Intercostal muscles (external, internal and innermost)
Blood vessels
Nerves
See figure
How are intercostal spaces named?
Named after the rib superior to it
What are the veins, arteries and nerves sandwiched between? where are they in relation to the rib?
The internal intercostal and the innermost intercostal
They are located in the costal groove
**order is vein, artery, nerve from superior to inferior
Is there a 12th intercostal space:
No
Inner linings of the thorax
Endothoracic fascia
Parietal pleura
See figure
What is the end-thoracic fascia attached to?
Ribs and muscles
What is the parietal pleura attached to?
Endothoracic fascia
What is the pleura?
Serous epithelial layer with sub epithelial connective tissue
What are the two parts of the pleura?
Visceral: attached to lung surface
Parietal: attached to the inner surface of the chest wall
These are separate cavities
Both are continuous at the root of the lung
What is the pleural cavity?
A potential space lined by the visceral and parietal pleura
What separates the visceral and parietal pleura?
A film of serous fluid
Reduces friction during breathing
Different parts of the parietal pleura
Cervical part: near the cervical vertebrae
Costal part: related to the ribs and intercostal space
Diaphragmatic part: covers the diaphragm
Mediastinal part: covers mediastinum
See figure
What are pleural recesses?
Potential spaces between the parietal and visceral pleura
When do the lungs expand into the recesses?
Usually only during forced inspiration
Clinical significance of recesses
provide potential spaces in which fluids can collect and from which fluids can be aspirated.
Where are the costomediastinal recesses? Where is the largest one?
Occurs on each side where costal pleura is
opposed to mediastinal pleura.
The largest is on the left side in the region overlying the heart.
Where are the costodiaphragmatic recesses?
Occur in each pleural cavity between the costal pleura and diaphragmatic pleura
Which recesses are most clinically important?
Costodiaphragmatic
Nerve innervation of the parietal pleura
Intercostal nerves: costal pleura
Phrenic nerve: mediastinal and diaphragmatic pleura
See figure
Nerve innervation of the visceral pleura (lungs)
Autonomic innervation by PSNS and SNS fibres
Does the parietal pleura have pain receptors?
No
What are the three surfaces of the lungs?
Costal
Mediastinal
Diaphragmatic
Anatomy of the costal surface of the lungs
Superior lobe
Middle lobe (right lung)
Inferior lobe
Oblique fissure
Horizontal fissure (right lung)
See figure
Which structures does the right lung have that the left lung does not have?
Middle lobe
Horizontal fissure
Impressions and grooves on the mediastinal surface of the lungs
Right: esophagus, azygous vein, right atrium
Left: Cardiac impression, aortic arch, left ventricle, lingula
Both have hilum and pulmonary ligament
See figure
What is the only root/attachment to the lungs?
Hium
What are the components of the hilum?
Pulmonary Artery (from pulmonary trunk)
Pulmonary Veins (drain into left atrium)
Bronchus
Autonomous nerves
Lymph nodes
Bronchial Arteries
Bronchial Veins
lymphatic vessels
Where does aspiration of foreign bodies most likely occur?
Right bronchus
Straighter and shorter
How many pulmonary veins per side enter the left atrium of the heart? How many pulmonary arteries exit?
2 pulmonary veins
One pulmonary artery
Lymphatic drainage from lungs and bronchi
See figure
Where do the lobes of the lungs drain?
The 3 lobes of the right lung and the lower lobe the left lung drain into the right lymphatic duct
The upper lobe of the left lung only drains into the left lymphatic (thoracic) duct.
Where does the thoracic duct drain?
Into the left-jugular subclavian junction
How does air enter the lungs during inspiration?
Muscles increase the thoracic space in all three of its dimensions
The parietal pleura is attached to the thoracic wall, forcing expansion of the lungs.
The pressure within the lungs drops below the atmospheric pressure outside, and the air passively rushes in (down the pressure gradient).
How does air leave the lungs during expiration?
Muscles of respiration relax.
The air in the lungs is then forced to move out of the lungs because of the high elasticity and retractility of the lung tissue.
See figure
What are the contours of the mediastinum?
Neck, arm
Left lung
Right lung
Abdomen
See figure
What are the three parts of the mediastinum?
Posterior
Middle
Anterior
See figure
What are the major organs of the mediastinum?
Thymus
Great vessels
Heart
Nerves
Trachea
Esophagus
Lymph vessels
What are the branches of the aorta?
Coronary arteries
Brachiocephalic trunk
Left common carotid artery
Left subclavian artery
Posterior intercostal arteries
Bronchial arteries
Esophageal arteries
Superior phrenic arteries
What are the branches of the aortic arch in ascending and descending order?
Ascending: Brachiocephalic (*), left common carotid (+), left subclavian (#)
See figure
What is the origin of the phrenic nerve? What does it supply?
Origin: cervical plexus (C3-C5)
Motor: diaphragm
Sensory: pericardium, parietal pleura (mediastinal, diaphragmatic), parietal peritoneum (underside of diaphragm)
What is the location of the phrenic nerve?
Ventral of anterior scalenus muscle
Descends anterior to the roots of the lungs
Between the fibrous pericardium and the mediastinal pleura
What are the nerves of the mediastinum?
Vagus
Phrenic
Recurrent laryngeal
Where does Vagus nerve run?
CN X
Runs posterior to root of lung
The right and left vagal trunks are adjacent to the esophagus
What does the vagus nerve contribute to?
Cardiac, Esophageal and pulmonary autonomous nerve plexus
Where does the recurrent laryngeal nerve branch from?
The vagus nerve
What does the recurrent laryngeal nerve innervate?
Motor: most of the muscles of the larynx
Sensory: inferior larynx
Course of the recurrent laryngeal nerve
Lateral to the trachea
Clinical significance of the recurrent laryngeal nerve
Apical lung cancer may cause hoarseness resulting from invasion of the recurrent laryngeal nerve
What provides sympathetic innervation of the mediastinum?
Sympathetic trunk (chain along the vertebral column)
Sphlanic nerves
Where do the PSNS nerves in the mediastinum derive from?
Vagus nerve
Function of SNS and PSNS nerves in the mediastinum
Pulmonary plexus
Esophageal plexus
Cardiac plexus
