Thorax, Tracheobronchial Tree & Lungs (Part 2) Flashcards
What is the mediastinum?
Central region bounded by the pleural cavities surrounded by lungs & just below the manubrium/sternal angle
How does the respiratory system develop?
- Respiratory diverticulum appears as an outgrowth of the gut tube; oesophagus separates from trachea via septum (4 weeks)
- Lung/bronchials then bud off of this
- Buds grow into splancho-pleuric mesoderm (week 5)
- Mesoderm forms blood vessels, cartilage, SM & visceral pleura
- Endoderm forms lining & glands
What 2 embryological things can go wrong in the development of the respiratory tract?
Issues separating trachea & oesophagus:
- Proximal atresia w/distal fistula: blind ended oesophagus at top and trachea-oesophageal link inferior to it
- Fistula: oesophagus goes into trachea & off of it again i.e. they have not separated properly
How do lung/bronchial buds branch embryologically?
Day 28: trachea branches into bronchial buds
Day 35: R and L secondary bronchus branch
Day 56: segmental bronchi develop (mesoderm divides with them too)
Week 16: all major lung parts developed
Week 26: respiratory epithelia begins to develop
7-10 years: full lung maturation
Why do babies who are born before 26 weeks have a much higher mortality rate?
Respiratory epithelia has not developed fully as this stage & therefore gaseous exchange cannot happen so the baby cannot breath (not much you can do as a doctor to speed up the development of this)
Describe the structure of the lungs.
R lung: 3 lobes (superior, inferior; middle); 2 fissures (oblique & horizontal) - 10 segments
L lung: 2 lobes (superior & inferior); 1 fissure (oblique) - 8-9 segments
ALTHOUGH this can vary
Why is the separation of lungs via lobes a good characteristic?
Disease, collapse or atelectasis can affect lobes independently
What are the anatomical relations of the lungs?
Rib 1
Diaphragm (& liver on R)
Oesophagus
Cardiac impression (L)
Veins: azygous, SVC & IVC (R) and brachiocephalic (both)
Arteries: subclavian, descending aorta & aortic arch (L)
What does the mediastinal surface of both lungs contain?
The hilum i.e. where all structures going to & from the lungs pass
What structures make up the hilum of the lungs?
Blood, vessels, nerves, lymphatics & airways:
Pulmonary artery
Pulmonary veins
Autonomic nerves
Main/lobar bronchi
Point of pleural reflection (parietal & visceral pleura) Pulmonary ligament (fold of parietal pleura)
Phrenic nerve passes anterior
What do the pulmonary vessels do?
2 pulmonary arteries (R & L) carry deoxygenated blood from heart to each lung
4 pulmonary veins (L & R superior + inferior) carry oxygenated blood from lungs to LA of heart
How can venous thromboses pass into the lungs?
Via pulmonary artery where it is then taken to the lungs (good at catching clots before they get to heart/brain)
What important nearby structures can be damaged by lung pathology? Whereabouts are they?
Vagus nerves: posterior to hilum & branches off into RLNs ->
R RLN: recurs at R lung apex under R subclavian artery)
L RLN: recurs at hilum/aortic arch)
Phrenic nerve: anterior to hilum
Describe the pleural layers of the lungs.
Visceral & parietal pleura surround lungs & held closely together via surface tension - potential space containing serous fluid between them called pleural cavity
Visceral covers lung surface into fissures & reflected at hilum as parietal pleura
Parietal pleura lines pleural cavity walls; costal, mediastinum, cervical & diaphragm
What are the different ways in which you can disturb the surface tension of the pleural cavity?
Pneumothorax Tension pneumothorax Haemothorax Chylothorax Pleural effusion
What is a tension pneumothorax?
Occurs when pressure of air trapped in the pleural cavity continues to increase
What will show on a chest X-ray if a patient has a tension pneumothorax?
Mediastinal shift Tracheal deviation Diaphragmatic depression Unilateral hyperinflation Increased intercostal space size Hyper-resonant
What do you do if a patient has a tension pneumothorax?
Needle decompression: stick needle into 2nd intercostal space at midclavicular line to relieve air
What are the surface markings of the lungs?
Tracheal bifurcation: 2nd cc or just below T4/5 (sternal plane)
Apex: sits behind + up to 2cm superior to medial 1/3 of clavicle
Horizontal fissure of R lung: 4th cc horizontally back to oblique fissure
Oblique fissure: T3 spinous process to 6th cc anteriorly
Bottom of lung: 10th rib paravertebral line posteriorly
Pleura & lung at end tidal inspiration (i.e. costodiaphragmatic recess): 12th rib paravertebral line posteriorly
Why is it important to know the surface markings of the lung fissures?
So you know what lung lobe you are listening to in clinical exam
Where do you auscultate the lung lobes?
Upper lobes: anteriorly
Middle lobes: laterally along axillary lines
Lower lobes: posteriorly
What is the costodiaphragmatic recess?
Region between lung & pleural reflection where parietal pleura reflects forming a recess between the thoracic wall & diaphragm
Why might you have a problem listening to the middle lung lobe?
Breast tissue may be in the way on the anterior side (why you listen to it laterally)
What pleural surface markings map the point of reflection (change of direction) of parietal pleura from thoracic wall i.e. costodiaphragmatic recess?
6th costal cartilage medial
Mid-clavicular line: 6th rib
Mid-axillary line: 8th rib
Can extend below 12th rib
What is the clinical relevance of the costodiaphragmatic recess?
Region for potential fluid accumulation i.e. pleural effusion
Where do the lungs move during breathing? Why?
Do not fill pleural cavity during normal breathing but lungs can expand into the costodiaphragmatic recess during deep inspiration as they are soft & compliant
What is the risk of procedures crossing the costodiaphragmatic recess? What would you ask the patient to do to reduce risk?
Risks lung damage i.e. pneumothorax
Liver, kidney & spleen damage
Ask patient to exhale so lung tissue is out of the way
What procedures may cause damage to the costodiaphragmatic recess? Why?
Renal operations & biopsy as it can extend below 12th rib
Where are chest drains inserted?
Revised triangle of safety:
- Anterior axillary fold (posterior border of Pec Major)
- Base of axilla
- Mid-axillary line
- Inferior part of 4th ICS (avoids damaging neurovascular bundle)
Why was the triangle of safety for a chest tube insertion revised?
Posterior border moved forward to avoid damaging the lung thoracic nerve as this nerve rotates scapula & patient will not be able to lift arm over 90 degrees if this is damaged
Where is the trachea?
Originates at lower end of larynx i.e. cricoid cartilage
Midline structure palpable via sternal notch
Bifurcates at T4/5 & enters lung hilum at T5/8
The right main bronchus is wider than the left. Why is this important?
Aspirations more likely to enter right bronchus due to less resistance
What is the cartilage like that lines the trachea?
Hyaline & C-shaped with gaps posteriorly
The carina of the trachea should look sharp. What could a swollen & rounded carina indicate?
Lymph nodes are immediately inferior so metastases or lymph node enlargement
What are the 3 right and left lung bronchi divisions in order from superior to inferior?
Main (primary)
Lobar (secondary)
Segmental (tertiary)
What are bronchopulmonary segments? What is the advantage of having them in the lungs?
Functionally independent wedge/pyramid shaped parts of the lung separated by fibrous tissue with apex’s directed towards hilum
Smallest functionally independent region of lung that can be resected without affecting other regions
So if a segmental/lobar bronchus gets atelectasis, that segment will collapse but the rest of the lung will be fine
Where do pulmonary arties & veins run in the lungs?
Artery: run with bronchi + bronchioles i.e. bronchial tree
Veins: between segments
What affects drainage of bronchopulmonary segments?
Gravity + posture
What procedures do functionally independent lung sections allow us to perform?
Pneumonectomy
Lobectomy
Segmentectomy (wedge resection)
Describe the structure of the bronchi.
Contain cartilage, SM + elastic fibres in their walls
Describe the structure of bronchioles.
No cartilage and walls mainly SM + elastic fibres
How do the airways split up after the segmental bronchus?
Subsegmental bronchi -> tertiary bronchioles -> respiratory bronchiole -> alveolar ducts, sacs + alveoli
Where do bronchial arteries arise from and what do they supply?
Aorta
Bronchi + lung connective tissue
What is the lymphatic drainage of the lungs?
Follows the tracheobronchial tree
Majority is to R lymphatic duct + R subclavian vein
EXCEPT left upper lobe which drains to the thoracic duct + L subclavian vein
What lymph structures are present in the lung from inferior to superior?
Hilar/bronchopulmonary nodes
Tracheobronchial nodes
Paratracheal nodes
Bronchomediastinal duct
