Block 2 Week 2 Thorax Tracheobronchial tree/ lungs part 2 Flashcards
What is the mediastinum?
Is the central region in the thoracic cavity bound by lungs within their pleural cavities
Where does the respiratory system develop from?
What is the name of the bud formed?
At what week does this occur?
At what week does outgrowth occur and describe what it contacts/ what forms from which layers
Respiratory system develops as an outpouching of the gut tube (endoderm) and forms what is known as the respiratory diverticulum. This occurs at 4 weeks.
The respiratory diverticulum grows out as multiple buds that start to form lung tissue at week 5. This diverticulum grows out and contacts the mesoderm which will form the blood vessels, cartilage of the trachea, smooth muscles and visceral pleura of the lungs.
The endoderm forms the respiratory epithelial lining and glands of the lung.
What needs to happen in order to develop a viable respiratory system?
The respiratory diverticulum and developing lungs need to separate from the gut tube. If they remain open this is incompatible with life.
At around 4/5 weeks a septation separates the trachea from the oesophagus.
What are two potential consequences of abnormal trachea-oesophageal septation?
1) Proximal atresia (absence or abnormal narrowing of an opening of the body) of the oesophagus and a distal fistula (connection between the trachea and oesophagus distally).
2) Fistula where there remains a connection between the trachea and oesophagus
Both defects need to be surgically corrected as they are incompatible with life.
what forms as the respiratory diverticulum outpouches?
Bronchial buds
What do the bronchial buds split into on the right and left sides?
Bronchial buds split into the right secondary bronchus with splits into 3 and on the left splits into the left secondary bronchus which further splits into two. Follows the pattern of lobes in the adult.
What do the R and L seconday buds split into?
The r and l secondary buds further split into segmental bronchi.
The mesoderm divides with the segmental bronchi forming the lobes.
At what week have all major structures developed apart from respiratory epithelium?
At what week does the respiratory epithelium start to develop and from which embryological layer?
What does this mean for lung function and what is the clinical relevance for premature babies?
By week 16 all major lung parts have developed except those for gas exchange.
It is not until week 26 that the lungs start to develop respiratory epithelia (from the endoderm) and become functional.
Clinical relevance and function: Before week 26 no respiratory simple squamous epithelia has developed in the terminal bronchi or alveoli, meaning no gas exchange can take place. This is why a premature baby has little chance of survival before 26 weeks as there is no way to force the development of respiratory epithelium.
How long does it take for full lung maturation to occur?
Full lung maturation doesnt occur until after 7-10 years of life.
Describe the lobes and fissures of the R vs L lung
What is the clinical relevance of the deepness of the fissures?
R lung: 3 lobes 1) superior 2) middle 3) inferior lobe
between superior lobe and inferior lobe is the oblique fissure
Between the superior and middle lobe is the horizontal fissure.
L lung: 2 lobes 1) superior 2) inferior
Split by an oblique fissure.
Fissures can run very deep, all the way to the hilum of the lung and completely separate the lobes of the lung. Diseases can affect different lung lobes separately without having any affect on the other lobes (E.g. superior lobe collapse on R side, middle and inferior lobe unaffected).
Which surface of the lung contains the hilum?
The mediastinal surface
what structures contact the mediastinal surface of the right lung- what impressions do they leave?
On the mediastinal surface more medial to the hilum are the IVC and SVC impressions.
Superior to the SVC impression is the brachiocephalic vein joining the SVC.
Laterally to the SVC is the azygous vein joining the SVC superiorly and running posterior to the hilum and inferiorly.
Sandwiched inbetween the azygous vein and hilum is the oesophageal impression.
Inferiorly on the right lung is the diaphragmatic impression (liver very closely related underneath).
What structures contact the mediastinal surface of the left lung and what impressions do they leave?
Again there is an impression of the oesophagus on the left lung (midline structure so contacts both the R & L lungs)
medially see large cardiac impression, inferiorly the diaphragmatic impression.
Superiorly to the cardiac impression you can see the arch of the aorta and the subclavian artery coming off it superiorly.
posterior to the hilum of the lung you can see the descending aorta and oesophagus.
What passes through the hilum of each lung?
Main bronchus, pulmonary arteries and 2 pulmonary veins along with nerves and lymphatics.
What clusters around the hilum?
many lymphatics
What surrounds the lung and thoracic cavity?
Two layers of pleura - parietal and visceral pleura surround each lung.
Visceral pleura covers lung surface, runs deep into the fissures and is reflected at the hilum as parietal pleura.
The parietal pleura lines the pleural cavity walls contacting the - costal surface, mediastinum, cervical region and diaphragm.
What holds the parietal and visceral pleura closely together?
Surface tension- normally this is only a potential space.
What happens if the surface tension in the pleural cavity is disturbed?
If surface tension in the pleural cavity is disturbed the intrapleural pressure will no longer be negative and this will compress the lung and affect respiratory function.
What can enter the pleural cavity in disease states and what is each called?
1) Air- pneumothorax
2) Blood- haemothorax
3) Lymphatic fluid- Chylothorax
What is pleural effusion?
Pleural effusion refers to a build up of fluid on the lung surface between the pleural layers. Fluid can come from a build up of fluid in the lung itself.
Where does the parietal pleura reflect and what is the fold of parietal pleura at this structure called?
Parietal pleura reflects at the hilum of each lung, the fold of parietal pleura is called the pulmonary ligament
Describe the levels of the structures in the hilum and what they carry
Superior in each hilum is the main bronchus (either R or L)
next down in hilum is the pulmonary artery that carries deoxygenated blood from the RV and pulmonary trunk (splits into R/L pulmnary artery).
most inferior are the pulmonary veins that drain oxygenated blood from the lungs back to the LA of the heart.
What nerve runs anterior to each hilum?
the phrenic nerve
What shape is the pulmonary trunk, what are its branches?
Classically a T shape
Splits into R and L pulmonary arteries
The R pulmonary artery continues as interlobular artery that splits to give superior, middle and inferior segmental branches.
The L pulmonary artery conties as interlobular artery that splits to give left superior lobe segmental branches and L inferior lobe segmental branches
What is a venous thrombosis? What would it have to travel through to reach the lungs?
What is it called when a venous thrombosis reaches the lungs?
A venous thrombosis is a blood clot that forms within the venous system. It would have to travel via the pulmonary arteries to reach the lungs. Once in the lungs it is called a pulmonary embolism.
Looking at the CT on the card notice the T shape of the Pulmonary trunk, the arch of the aorta (two circular structures) and the darker region which is a clot in the left pulmomary artery.
What important nerves pass through the mediastinum and where are they in relation to the hilum of each lung?
The phrenic nerve passes anteriorly to the hilum of each lung
The vagus nerve passes posteriorly to the hilum of each lung and gives off recurrent branches - the L/R recurrent laryngeal nerves.
Describe the passage of the vagus nerve on the right side of the mediastinum, what could pathologically affect the important branch coming off this nerve?
The right vagus nerve will pass posteriorly to the hilum of the right lung and loop back round to give off the right recurrent laryngeal nerve. It slips underneath the R subclavian near the apex of the lung.
Pathology: a Pancoast tumour of the apex of the lung could compress the right recurrent laryngeal nerve and cause hoarseness of voice.
Describe the passage of the left vagus nerve over the left mediastinum and what pathology can affect the important branch it gives off?
The left vagus nerve travels posterioly to the hilum of the left lung and arches back to give off the left recurrent laryngeal nerve. This arches back at the arch of the aorta.
Aortic aneurysm could compress the left recurrent laryngeal nerve causing hoarseness of voice.
What are the classical signs of a tension pneumothorax on a chest X-ray?
And in respiratory examination? (resonance)
Mediastinal shift, loss of heart shadow and shift
Tracheal deviation to one side
Diaphragmatic depression
Unilateral hyperinflation
Increased intercostal space size
Hyperresonance
How do you treat a tension pneumothorax?
Needle decompression (wide bore needle) in the 2nd intercostal space in the midclavicular line to relieve the build up of air.
Where does the apex of the lung sit in relation to the clavicle?
Apex sits above and superior to the medial 1/3 of the clavicle (around 2cm above).
What is the relevance of the sternal angle?
1) know it is T4/5 where tracheal bifurcation occurs
2) know 2nd costal cartilage articualtes here- therefore you can count ribs
3) Needle decompression midclavicular line in 2nd intercostal space
What level are the fissures on the right lung?
How would you find them?
How does this help auscultation?
Anteriorly: Know that horizontal fissure starts at the 4th costal cartilage (find by counting down two ribs from sternal angle).
Trace back horizontally to the oblique fissure.
Auscultate upper lobe anteriorly above the horizontal fissure.
Below horizontal fissure know it is the middle lobe. Auscultate anteriorly but laterally to avoid breast tissue/pectoralis major (in midaxillary line).
Oblique fissure found on posterior of the patient by asking them to abduct their arm and using the medial border of the abducted scapula. It begins at the T3 vertebra (can be found by using bony prominence of C7 on posterior and walking down vertebra). Then follow the line of the medial border of abducted scapula.
Allows us to ausculate inferior lobe on posterior of patient.
What and where is the costodiaphragmatic recess? (think surface anatomy)
The costodiaphragmatic recess is the space created by the reflection of the pleura between the lateral thoracic wall and the diaphragm overlying the liver.
Found: Posteriorly from T10 in the paravertebral line (horizontal from T10)
extends to T12 in the paravertebral line (horizontal line drawn across from T12).
Anteriorly: Sits approximately 2 ribs below where the actual lung finishes (medially at 6th costal cartilage, extends to 8th rib mid axillary line) so medially from 6th costal cartialge down to the 10th rib mid axillary line.
Why is a procedure crossing the costodiaphragmatic recess risky?
What would you ask a patient to do immediately before a procedure in the CDR?
Costodiaphragmatic recess is closely related to the liver, kidneys and spleen which are at risk of damage during a procedure. The lungs only extend into this space during inspiration, in order to access space ask patient to exhale immediately prior to procedure in this region.
During a chest tube insertion the triangle of safety is used. Describe the boundaries of the triangle of safety and what structures form it/ lie close to it.
What could happen in nerves within/near this region are damaged?
Borders:
Anterior: anterior axillary fold ,posterior border of pectoralis major
posterior: posterior axillary fold, midaxillary line
used to be formed by the anterior border of latissimus dorsi but the border has been moved forward due to the risk of damage to the long thoracic nerve.
The long thoracic nerve innervates the serratus anterior muscles which is responsible for rotating the scapula during abduction of the arm. Damage to this nerve leads to inability to abduct the arm from the midline.
Chest tube inserted inbetween these borders in the 4th intercostal space, in inferior portion to avoid damage to the Neurovascular bundle in the costal groove. (inferior part of ribs)
What is the bifurcation of the trachea called?
What does this region look like on endoscope?
What can be seen in the R and L main bronchi walls and what is their function?
1) the carina
2) sharp
3) rings of hyaline cartilage - maintain the bronchi in open state
How are the divisions of the bronchi described?
Each main bronchus known as a primary bronchus.
The next divisions are known as secondary or lobar bronchi
These split again and are known as tertiary or segmental bronchi
What are bronchopulmonary segments? Desribe their structure/ supply.
In each lobe there are multiple functionally independent pyramidal wedges of lung tissue.
They are the smallest functionally independent region of the lung that can be resected without affecting other regions.
The apex of each bronchopulmonary segment is directed towards the hilum.
Each segment has its own air and blood supply.
Tertiary bronchi bring air into each segment.
Fibrous tissue separates the segments.
Pulmonary arteries run with the bronchi and bronchioles.
Pulmonary veins run inbetween each segment.
How does gravity/posture affect drainage of a bronchopulmonary segment?
If a patient is supine (lying down) gravity can pool blood into the inferior aspect of the lung, into the apical/superior portion of the inferior lobe which is now the most inferior portion of the lung.
Pulmonary artery branches run along ___________
Pulmonary vein branches run ________ ___________.
pulmonary artery branches run along the bronchial tree
Pulmonary veins run inbetween segments.
Describe the lymphatic drainage of the lungs
Lymphatic drainage from the lungs follows the tracheobronchial tree.
From hilar nodes to tracheobronchial nodes, to paratracheal nodes to bronchomediastinal duct into the subclavian.
Majority of the lymphatic drainage (except the left upper lobe) is to the right subclavian vein
The left upper lobe drains directly into the left subclavian vein
