Trachea, main bronchi, broncho-pulmonary segments Flashcards
Trachea: origin and termination
- Originates from the inferior surface of the cricoid cartilage (a laryngeal structure)
- Most superior structure of the trache is the cricotracheal ligament, which connects the cricoid cartillage with the first tracheal ring
- Terminates at its bifurcation into right and left main bronchi at the carina (T4/5 level)
What is the cricotracheal ligament? Clinical importance?
Most superior structure of the trachea
Connects the cricoid cartilage with the first tracheal ring
Can be used to access the airway during emergency oxygenation with a needle placed directly into the trachea
Trachea: cervical and thoracic components
- Approximately equal length (5-6cm each)
- Cervical component runs from cricoid cartillage (C6) to sternal notch (T2/3). Easily accessible to ENT surgeon
- Thoracic component: sternal notch to tracheal bifurcation at carina (T4/5). Lies in mediastinum, requires thoracotomy for surgical access
Trachea: structure and lining
- 12-20 C-shaped cartilagionous rings
- Rings are incomplete and the trachealis muscle completes the posterior wall
- Lining: pseudostratified columnar epithelium with mucus glands
Trachea: length and diameter.
What factors affect this
- Approx 12cm long in adult
- Length is increased by several centimetres during inspiration
- 1.6-2cm in diameter
- Wider in the male
- Diameter is narrowed by contraction of trachealis
Trachea: functions (4)
- Physical tube forming part of the continuous airway from the external atmosphere to the alveoli
- Mucus layer traps small inahled particles. Coordinated beating of cilia transports the particles to the larynx -> swallowed or expectorated
- Mucus layer warms and humidifies gas in airway
- Takes part in cough reflex
Trachea: role in the cough reflex
- Afferent limb: sensation from trachea via vagus nerve
- Motor response: vigorous cough + contraction of trachealis -> narrowed diameter of the trachea increases the speed of the expulsive airflow
Note: velocity of gas flow during vigorous coughing exceeds the speed of sound
Relations of cervical portion of the trachea
C6 to T2/3
Anterior:
* Thyroid isthmus
* Inferior thyroid veins
* Strap muscles (sternothyroid and sternohyoid)
* Cervical fascia
* Subcutaneous tissue and skin
Lateral
* Carotid sheath: common carotid arteries, internal jugular vein, vagus nerve
* Right and left lobes of the thyroid gland
* Inferior thyroid arteries
Posterior:
* Oesophagus
* Recurrent laryngeal nerves on each side run in the groove between the trachea and oesophagus
Relations of thoracic portion of trachea
T2/3 (sternal notch) to T4/5 (carina)
Anterior:
* Skin, subcutaneous tissue
* Manubrium sterni
* Thymus (remnants)
* Left innominate vein
* Aortic arch or great vessels arising from the aorta
* Cardiac plexus
Lateral, on the right:
* Pleura
* Innominate artery
* Vagus nerve
Lateral, on the left:
* Recurrent laryngeal nerve
* Aortic arch
* Left common carotid and subclavian arteries
Anatomical relationship between trachea and oesophagus, clinical implications
- Oesophagus lies posterior to the trachea throughout its entire length
Implications:
* Oesophageal tumours may cause airway obstruction,
* Long-standing oesophageal foreign bodies may erode into the trachea
* Back wall of the trachea may be damaged during surgical resection of the oesophagus
Trachea: blood and nerve supply
- Arterial: inferior thyroid arteries, internal thoracic arteries, branches of the bronchial arteries
- Venous drainage: inferior thyroid veins
- Parasympathetic supply to smooth muscles and veins: either vagus nerve directly or recurrent laryngeal nerves
- Sympathetic nerve supply: sympathetic trunk
Position of the carina and right main bronchus
- In the supine patient: T4/5, surface marking = sternomanubrial junction (angle of Louis)
- Descends inferiorly in the erect patient & during inspiration, to at least T6/7
- In adults, R main bronchus is larger and in a more direct line with the trachea than the left -> carina may appear to the left of the midline of the trachea
Image from trachea during bronchoscopy. Note trachealis muscle posteriorly, incomplete tracheal rings, and carina
Carina: surrounding structures
Lies in the superior mediastinum, slightly to the right of the midline.
Anteriorly: main trunk of pulmonary artery divides into right and left pulmonary arteries, usually just to the left overlying the left main bronchus
Posteriorly: oesophagus
Aorta wraps around:
* Ascending aorta passes in front of pulmonary artery -> aortic arch, which passes to the left of the trachea -> arches over the left main bronchus
* Because the aorta is on the left, the lower trachea is slightly to the right of hte midline
* The branches of the aortic arch hug the lateral borders of the lower trachea: brachiocephalic artery on right, left common carotid on the left
Tracheobronchial tree: what is the sequence of airways?
- Trachea
- Main bronchus (2)
- Lobar bronchus (5 - to 5 lobes of lung)
- Segmental bronchus (19-20, to the bronchopulmonary segments)
- Terminal bronchioles
- Respiratory bronchioles (connected to alveolar sacs)
- Alveolar duct
- Alveolar sacs
- Alveoli
The tracheobronchial tree branches into progressively narrower tubes. The tracheobronchial wall initially maintains the cartilaginous ring structure until the branches are about 1 mm in diameter (then called bronchioles)
Main bronchi (size, names)
Trachea divides into right and left main (primary) bronchi at the carina
Right main bronchus: shorter and wider
* Upper limit of diameter in males: 21mm
* 25mm long
* ‘Bronchus intermedius’ = portion immediately distal to the origin of the right upper lobe. Continuation of the right main bronchus beyong the upper lobe to the origins of the middle and lower lobes. 30mm long.
Left main bronchus: longer and narrower
* Upper limit of diameter in males: 18mm
* 50mm long
Lobar bronchi (names, origin, supply)
Right lung lobar bronchi:
* Right upper -> supplies right upper lobe
* Right middle -> supplies right middle lobe
* Right lower -> supplies right lower lobe
Left lung lobar bronchi:
* Left upper -> supplies left upper lobe + lingula
* Left lower -> supplies left lower lobe
All origins of lobar and segmental bronchi are intrapulmonary, except the **right upper lobar bronchus, which arises about 2.5cm from carina **
Bronchopulmonary segments of left lung (number, names)
8-10 bronchopulmonary segments in the two lobes of the left lung
Common arrangement of 9 bronchopulmonary segments (medial basal/ ‘cardiac segment’ lost as result of ‘intrusion of heart into space occupied by left lung:
Upper lobe, including lingula:
* Apical
* Posterior
* Anterior
* Superior
* Inferior
Lower lobe
* Apical (or superior)
* Anterior basal
* Lateral basal
* Posterior basal
Bronchopulmonary segments of right lung (names, number)
10 bronchopulmonary segments in the three lobes
APALM AMALP
Upper:
* Apical
* Posterior
* Anterior
Middle:
* Lateral
* Medial
Lower:
* Apical
* Medial basal
* Anterior basal
* Lateral basal
* Posterior basal
