Block 2 Week 2 Thorax/ Tracheobronchial tree/ lungs Flashcards
Describe the thorax and its composition/boundaries/apertures
The thorax is an irregular cylindrical cavity with 2 apertures, the superior and inferior apertures that allow important structures to enter/leave the thoracic cavity.
Boundaries: by the diaphragm inferiorly, ends at costal margin.
By the thoracic cage laterally.
Posteriorly by the thoracic vertebra
Anteriorly by the sternum, ribs and costal cartilages
Within the thoracic cage is the pleural cavity made of parietal and visceral pleura. Within the pleural cavity is the mediastinum which houses the heart and great vessels.
Describe the structure of the thoracic cage
Thoracic cage is made up of 12 ribs that attach posteriorly to the thoracic vertebra and (1-10) insert anteriorly via their costal cartilages onto the sternum. In between the ribs are the intercostal muscles which pull the ribs up/down during inspiration/expiration. Ribs 11 and 12 are flaoting ribs and do not end in cartilage but are embedded in muscle.
what is the function of the thorax?
Provides passageway between the abdomen and neck/upperlimb
Protection and breathing
Describe the layers of the thoracic wall
- Skin
- Subcutaneous fat
- Muscle layers- External intercostal, internal intercostal, innermost intercostal (in between ribs) (Inbetween the inner intercostal muscle and innermost intercostal muscles is the neurovascular bundle with Vein Artery Nerve).
- parietal pleura
- intrapleural space
- visceral pleura
- lung
What joints are between the ribs and thoracic vertebra- why is this important?
Synovial joints, allows movement of thoracic cage during inspiration and expiration.
Thoracic cage= mobile yet has structural rigidity
Rib fractures can lead to paradoxical movement of the thoracic wall segment: describe this
On normal inspiration ribs are elevated by the external intercostal muscles that pull the rib up by bucket-handle effect. When a rib is fractured it is no longer anchored to the sternum/thoracic vertebrae meaning when muscles contract and there is a drop in intrapleural pressure, the rib is depressed downwards during inspiration and pushed out during expiration.
Describe the superior thoracic aperture- its boundaries and what passes through it.
What is the clinical relevance of this?
Bound anteriorly by the manubrium of the sternum, the joint between the first rib and posteriorly by Rib 1 joining the T1 vertebra.
Structures that move through are the subclavian vessels (vein and artery) , common carotid arteries and internal jugular veins. Centrally have the trachea and oesophagus.
The brachial plexus (C5/C6/C7/C8/T1) also passes through here.
Clinical relevance: these vessels and nerves are quite vulnerable. Ca be damaged by trauma, tumour or cervical rib. A cervical rib ( where an extra rib forms at C7) could compress these vessels and damage the brachial plexus.
What do you notice about the 1st dorsal webspace? What is this caused by?
There has been muscle atrophy in the 1st dorsal space. Caused by loss of innervation via the brachial plexus (C5/6/7) due to compression by a cervical rib.
Describe the sternum, its ossification, parts, angles, vertebral levels and relevance of this.
Sternum is formed of three parts, the manubrium, body and xiphoid process (finishes at T9/10 good bony landmark). At the top of the sternum is the suprasternal/jugular notch at the level of T2. Where the manubrium meets the body there is the sternal angle which can be palpated.
The sternal angle is at T4/T5 and this is where the trachea birfucates, marks where the arch of the aorta begins and ends. Also know that rib 2 articulates at the sternal angle. Useful for counting ribs.
Sternal angle splits the thoracic caivty into superior and inferior portion.
Sternum fully fuses later in life (25 yrs)
Are fractures of the sternum common?
No- fractures of the sternum are rare and often fatal.
Describe structure of the individual rib
Each individual rib is formed by a head, neck, bony tubercle, angle, body and ends in costal cartilage anteriorly(1-10) or in muscle (11 and 12). The angle of each rib is used by anaesthetists to perfrom intercostal nerve blocks. They articulate with the thoracic vertebra posteriorly. On inferior aspect of each rib is a costal groove in with the intercostal neurovascular bundle sits (VAN).
Describe the articulation of the ribs with the thoracic vertebra and sternum
Thoracic vertebra has 3 sites on each side for articulation with the ribs.
Two demifacets are located superior and inferior on the vertebral body. Superior costal facet articulates with the head of its own rib and the inferior costal facet articulates with the head of the rib below. The transverse costal facet on the transverse process articulates with the tubercle of its own rib.
Describe 3 classification of the ribs
Ribs 1-7 known as vertebrosternal ribs- they articulate with the thoracic vertbera posteriorly and the sternum via costal cartilage anteriorly.
Ribs 8/9/10 Vertebrocostal ribs that articulate with thoracic vertbera posteriorly and insert onto the costal cartialge of rib 7 anteriorly so indirectly onto the sternum.
Ribs 11 and 12 are the floating ribs that articulate with the thoracic vertebra posteriorly and end in muscle (no costal cartilage @ end).
What is contained within the intercostal space? What is the function of the structure?
Intercostal spaces lie between adjacent ribs are filled by 3 layers of intercostal muscles 1) external 2) internal 3) innermost
Between the internal and innermost is the neurovascular bundle on inferior margin of rib in costal groove.
External intercostal runs from inferior margin of rib above down to superior margin of rib below. Innervated by intercostal nerves (T1-11). Active during inspiration, moves ribs superiorly.
Internal intercostals originate from lateral edge of costal groove and inserts into superior surface of rib below. Innervated by intercostal nerves (T1-T11), depress ribs during expiration.
Innermost intercostals deepest layer, originate from medial edge of costal groove and insert into superior surface of rib below, innervated by T1-11 intercostal nerves, act with internal intercostals, depress ribcage.
Where should you insert a chest drain and why?
Chest drains should be inserted into the inferior part of the intercostal spaces (above superior surface of rib) to avoid damaging the main neurovascular bundle in the costal groove on inferior aspect of each rib.
Describe how the intercostal nerves innervate the thoracic wall, give reference to their branches, spinal cord level and what they innervate
The intercostal nerves are anterior rami of spinal nerves T1 - T11 and lie in the intercostal spaces inbetween adjacent ribs.
Intercostal nerve passes laterally around the thoracic wall in an intercostal space, and pierces the 3 layers- forming lateral cutaneous branch. This lateral cutaneous branch divides into an anterior and posterior branch that innervate overlying skin.
Intercostal nerves end as anterior cutaneous branches that pierce the intercostal space parallel to the sternum, supply anterior skin.
Intercostal nerves supply the 3 intercostal muscles, somatic sensory innervation to the skin/cartilage/bone/parietal pleura.
Describe the innervation pattern of intercostal nerves and what would happen if the nerve was damaged by:
1) chest tube insertion
2) shingles
Intercostal nerves (anterior rami of spinal nerves T1-T11) , branch into:
1) posterior ramus- skin on back
2) Lateral cutaneous branch which splits into anterior and posterior innervaes skins lateral wall
3) Anterior cutaneous branch innervates skin on anterior thoracic wall
Forms dermatomal pattern of innervation.
Damage by test tube insertion would lead to numbness in the area of skin/cartilage/bone/parietal pleura supplied
Reactivation of latent chicken pox virus in the dorsal root ganglion of spinal nerves can spread via intercostal nerves and has a dermatomal pattern of infection.
What are the facial symptoms of Horner’s syndrome?
PAM
Ptosis- dropping eyelid
Anhydrosis- loss of sweating
Miosis- Pupillary constriction
Often unilaterl presenation due to tumour on one side- loss of sympathetic innervation on that side.
What is the arterial supply to the thoracic wall? Describe the main arteries, their origins and their course.
What is the relevance of this in the event of aortic narrowing/coarctation?
Arterial supply to the thoracic wall is via anterior and posterior intercostal arteries.
The posterior intercostal arteries arise directly off the descending aorta.
Off the subclavian artery runs another artery that projects down parallel to the sternum called the internal thoracic artery. This artery then becomes the musculophrenic when it passes under the costal margin.
The anterior intercostal arteries arise from the internal thoracic and musculophrenic artery.
The anterior intercostal arteries run back and join the posterior intercostal artery forming an anastomoses.
This allows collateral circulation in the event of aortic coarctation (narrowing).
Why are internal thoracic arteries special?
Internal thoracic arteries are special as they:
1) allow collateral circulation via anterior intercostal arteries which anastomose with the posterior intercostal arteries to the thoracic wall in the event of aorta narrowing/coarctation
2) they resist plaque build up better than other arteries in the body
3) can be used for coronary arterial bypass grafting (CABG)
Describe the venous drainage of the thoracic wall, naming the major veins involved, their final destination and why the upper portion of the thorax is different.
Drainage of the thoracic wall is by an UNPAIRED azygous system.
Each intercostal space has a vein that needs to drain into the azygous system.
On the right side intercostal veins drain into the Azygous vein that runs parallel to the posterior thoracic wall.
On the left side intercostal veins drain into two accessory veins the 1) accessory azygous vein 2) hemiazygous vein before they join the azygous vein on the right side.
The azygous vein then joins the superior vena cava.
The upper intercostal spaces drain directly into the brachiocephalic veins.
What is the structure shown in the image? (blue arrow)
Azygous vein joining the SVC
What is the thoracic duct?
main vessel of the lymphatic system passing in front of the spine and emptying into the left brachiocephalic vein. Drains the majority of the body’s lymph fluid
.
Describe the course of the thoracic duct
The thoracic duct beigns at the cisterna chyli which is a dilation of the lymphatic system (on the right of the abdominal aorta).
Runs through the posterior and superior mediastinum, anterior to the vertebral bodies.
Empties into the left subclavian vein
There are many lymph nodes around the subclavian vein due to high level of lymph drained here.
Describe the structure of the diaphragm
What are its attachments?
Consists of R & L domes that are muscular.
Off R dome arises R crus from L1-L3 vertebra and some of the fibres surround the oesophageal opening forming physiological sphincter that prevents reflux.
Off L dome arises L crus from L1-L2
Muscles fibres of the diaphragm continue to form central tendinous portion that underlies the heart.
Diaphragm attaches to: Lumbar vertebrae posteriorly, and to ribs 10-12. Anteriorly to costal margin (ribs 7-10) and Xiphoid process.
What is the innervation of the diaphragm?
Phrenic nerve (C3/4/5 keeps the diaphragm alive!) which splits into R and L phrenic nerves.
Provides both motor and sensory innervation to the diaphragm
Why might inflammation of the gallbladder refer pain to the right hypochondrium and right shoulder?
The gallbladder sits in the midclavicular line in line with the 9th rib.
Infammation of the gallbladder can contact the diaphragm which is innervated by C3/4/5. Shoulder region is also innervated by these nerves and therefore can get referred pain to the shoulder.
Pain in the R hypochondrium is due to irritation of the intercostal nerves in that area that will refer the pain to that dermatomal region.
What is unilateral damage to the phrenic nerve called and what might it cause?
Hemidiaphragmatic palsy- cause loss of innervation to the diaphragm on one side, diaphragm will not move down during inspiration causing breathing diffuculty
What are the three openings in the diaphragm and at what vertebral levels do they occur?
I 8 10 Oranges at 12.
1) inferior vena cava- T8
2) Oesophagus - T10 (classically - more recent data suggest T11/12)
3) Aorta - T12
What is the name of a posterolateral diaphragmatic hernia
Bochdalek hernia- due to congenital abnormality you can get herniation of abdominal organs into the pleural cavity through abnormal opening of the diaphragm on posterolateral wall
What is the name of a retrosternal herniation through the diaphragm?
Morgagni hernia - herniation parallel to or behind the sternum due to congenital abnormality - opening through diaphragm can get abdominal organs through this hole
