Thorax, Tracheobronchial Tree & Lungs (Part 1) Flashcards
What is the thorax?
Irregularly cylindrical cavity with openings at top & bottom composed of a thoracic wall, pleural cavities & mediastinum
What are the functions of the thorax?
Passageway between abdomen & neck/upper limb for vessels & nerves
Protection of organs
Breathing
What are the 2 openings of the thorax called?
Superior thoracic aperture
Inferior thoracic aperture
What is the bottom boundary of the thorax?
Diaphragm
What is within the mediastinum?
Heart
Great vessels
How does the thoracic wall allow breathing?
Able to withstand a range of positive & negative pressures during breathing
Mobile structure but with structural rigidity
Describe the structure of the ribs.
12 paired ribs with intercostal muscles in between
Ribs 1-10 end in costal cartilage whilst 11-12 embedded in muscle
Articulate with thoracic vertebra posteriorly around the thoracic inlet and connect to the sternum via costal cartilage anteriorly with variable articulations
Why can ribs move?
Articulation of ribs have synovial joints
What will happen if the ribs are fractured in terms of breathing?
Paradoxical movement of thoracic wall segment at point of fracture; ribs will not move normally e.g. they will depress rather than expand in inspiration
What is the lower border of the costal cartilage called?
Costal margin
What structures go through the thoracic apertures?
Part of brachial plexus
Subclavian vessels
What can happen if you are born with an cervical rib (at C7 instead of T1)?
May compress brachial plexus -> 1st dorsal webspace of hands looks deflated as these muscles are innervated by the brachial plexus and they atrophy due to lack of stimulation
What parts make up the sternum from the top down?
Suprasternal (jugular) notch (T2) Manibrium Manubrio/sternal angle (T4/5) Body Xiphoid process (T9/10)
What bit of the sternum is useful to palpate? What does this give you an indication of?
Sternal angle
Indicates that the 2nd costal cartilage is lateral & the sternal plane (T4/T5 IV disc)
Also divides sternum & mediastinum into superior & inferior parts
Are fractures of the sternum common?
No, usually only seen with serious of fatal injury
Where are the costal grooves of the rib? Why are they relevant?
On inferior margin
Where neurovascular bundle runs (collateral & accessory bundles inferior too)
What is the rib angle useful for?
Used by anaesthetists as a landmark to perform intercostal nerve blocks
What is in the neurovascular bundle in order?
V: Vein
A: Artery
N: Nerve
What do most ribs articulate with?
Bodies of their own vertebra (w/ synovial joints) AND one above it AND with transverse process of their own
What are the 3 classifications of the ribs and what ribs does each one cover?
- Vertebrosternal (ribs 1-7)
- Vertebrocostal (ribs 8-10)
- Floating ribs (ribs 11-12)
What are the 3 layers of intercostal muscles that fill the intercostal spaces?
- External intercostal muscle
- Internal intercostal muscle
- Innermost intercostal muscle
What muscle layers does the neurovascular bundle run between?
Internal & innermost intercostal muscles
What is the function of the intercostal muscles?
Provide support & contribute to thoracic wall movements
What muscles control inspiration and expiration mainly? What do they do?
Inspiration: external intercostal muscles (move downwards)
Expiration: internal intercostal muscles (move upwards)
Where should chest drains be inserted? Why?
Inferior part of intercostal spaces to avoid damaging the MAIN neurovascular bundle
What layer is on the inside of the innermost intercostal muscle?
Endothoracic fascia
Where do the intercostal nerves come from and what do they innervate?
Ventral rami of spinal nerves
Provide motor & sensory to the intercostal space & surrounding tissue (e.g. skin, cartilage, bone, muscle & parietal pleura)
Why is the dermatomal arrangement of intercostal nerves relevant clinically?
Pleuritic pain can refer to dermatome
Shingles can distribute to dermatome
Where does the sympathetic chain run?
Along posterior thoracic wall (T1-L2)
What can compress the sympathetic chain in its apical region? What can this cause? Why?
Pancoast tumour i.e. apical lung tumour
-> Horner’s syndrome; this chain sends branches to head & neck so symptoms will show in face mainly e.g. ptosis, miosis & loss of hemifacial sweating (on same side as tumour)
Describe the arrangement of the anterior (AIA) and posterior intercostal arteries (PIA).
PIA from descending aorta & AIA from internal thoracic artery + musculophrenic -> join to form anastomosis in middle
Allows a collateral circulation that can provide a potential bypass in aortic coarctation
What can the internal thoracic arteries (ITA) be used for? Why?
Coronary artery bypass grafting (CABG) because ITA resists plaque build up better than most arteries in body so good to harvest & replace a artery that doesn’t work anymore
How is the thoracic wall drained?
Unpaired azygous system:
- Upper intercostal spaces drain directly in brachiocephalic veins -> subclavian veins
- Right sided structures drain in azygous vein -> SVC
- Left sided structures drain via accessory azygous/hemiazygous veins-> cross midline into azygous -> SVC
Where is the thoracic duct? What does it do?
Runs through posterior & superior mediastinum, anterior to vertebral bodies
Drains majority of bodies lymph fluid into left subclavian vein
What is special about the left subclavian vein?
Extra supraclavicular nodes sit around this region due to the amount of lymph fluid draining at this point
What is the diaphragm?
Muscular & tendinous structure that domes into the thoracic cavity & fills inferior thoracic aperture
What are the characteristic features of the diaphragm?
Right & left domes
- Central tendinous part for heart
- Attaches to costal margin & ribs 10-12
- Diaphragmatic crura attach to lumbar vertebrae
What happens to the diaphragm during inspiration?
Drops down & flattens = thoracic cavity volume increases -> decreased pressure allowing air to move into the lungs
Describe the innervation of the diaphragm.
Phrenic nerve (C3-5) provides motor & sensory
Additional sensory innervation on periphery from intercostal nerves
What will occur if there is unilateral damage to the phrenic nerve?
Hemidiaphragmatic palsy
Where can gallbladder inflammation cause pain?
Shoulder due to the phrenic nerve
Regional pain in right hypochrondium due to intercostal nerve
As its in the midclavicular line around the 9th rib
What structures pierce the diaphragm? Why can this be problematic?
IVC (T8)
Oesophagus (T10-12)
Aorta (T12)
Creates relative weak spots through which a sliding or rolling hernia can form
Where can congenital diaphragmatic defects occur?
Posterolaterally (Bochdalek): part of liver pops up into diaphragm
Retrosternally (Morgagni): tranverse colon & greater omentum coming up behind diaphragm behind midline of sternum
If severe must be fixed early in life
The diaphragm separates the thoracic cavity from the ___ __.
Abdominal cavity
