The trachea extends from the inferior border of the larynx at vertebral level C6/7 to bifurcation of trachea into right and left main bronchi at T4/5 (the level of the sternal angle). The trachea consist of many C-shaped cartilage rings with the trachealis muscle (smooth m) located posteriorly.
Location of the trachea in the neck
The trachea is situated in the midline, partially covered anteriorly by infrahyoid (strap) muscles and isthmus of thyroid gland. Posterior to the trachea is the oeseophagus and vertebral bodies.
Anatomic relationship between arch of aorta and trachea
The arch of aorta is located anterior and to the left of the trachea.
The trachea bifurcates into the main (primary) bronchi at vertebral level T4/5.
The difference between the right and left main bronchus.
The right main bronchus is more vertical and wider than the left main bronchus therefore aspirated objects are more likely to go into the right bronchus.
A cartilaginous ridge located at the bifurcation of the trachea, slightly to the left of the midline. It is particularly sensitive to irritation producing a strong cough reflex.
The thoracic cavity
Is divided into two pulmonary cavities (laterally) containing the lungs with the mediastinum, located centrally, containing the heart, great vessels, trachea, oeseophagus etc.
A continuous seorus membrane (simple squamous epithelium and underlying CT) covering the lungs (visceral pleura) and the thoracic wall, diaphragm and mediastinum (parietal pleura). The visceral and parietal pleura are continuous at the hilum of the lung.
A potential space between visceral and parietal pleural layers containing a thin film of serous fluid. It surrounds lung but the lung is not 'in' it. The left and right pleural cavities are separate and not connected.
Excess fluid in the pleural cavity
Blood in the pleural cavity
Air in pleural cavity
Is divided into:
- Cervical (superior)
- Diaphragmatic; and
Innervation of parietal pleura
The parietal pleura is innervated by pain fibres (but visceral pleura isn't).
- Inercostal nn invervate the costal and peripheral diaphragmatic pleura
- Phrenic n (C3-5) innervates the mediastinal and central diaphragmatic pleura - pain referred ot neck, shoulder.
Lines of pleural reflection and recess
Occur where the parietal pleura reflects from one surface to another.
- Costodiaphragmatic recess is located at the junction of teh costal and diaphragmatic pleura.
- Costomediastinal recess is located at the border of the mediastinal pleural and costal pleura.
Lung borders and surfaces
The lung has three surfaces (costal, diaphragmatic, mediastinal) an apex and three borders (anterior, posterior, inferior).
Hilum of lungs
Also known as the 'root' of the lung.
- Connects the lungs to the mediastinum.
- The parietal and visceral pleura are coninuous at the hilum.
- Contains pulmonary veins, pulmonary artery, bronchus, nerves, bronchia aa vv, lymphatic vessels and nodes.
Right lung anatomy
The right lung has three lobes (upper, middle, lower) and two fissures oblique and horizontal.
The pulmonary a, vv and bronchus are located in the hilum with the pulmonary ligament extending inferiorly from the hilum.
Left lung anatomy
The left lung has two lobes separated by an oblique fissure
- Upper: with lingual and cardiac notch
The main (primary) bronchi divide into two secondary bronchi to upper and lower lobes on the left and three secondary bronchi to the upper, middle and lower lobes on the right.
Secondary bronchi divide into tertiary (segmental) bronchi which supply bronchopulmonary segments. Tertiary bronchi divide many times to eventually become bronchioles (lack cartilage).
There are 10 segments on the right and 8 (or 10) on the left.
One segmental (tertiary) bronchus and one segmental pulmonary artery supply each bronchopulmonary segment. Each bronchopulmonary segment is pyramidal in shape with the apex towards the lung hilum and the base at the pleural surface, and each segment is separated by CT.
- Right atrium
- Right ventricle
- Pulmonary trunk
- Pulmonary arteries
- Lobar arteries
- Segmental arteries...
- Capillaries (gas exchange)
- Pulmonary veins
- Left atrium
- Left ventricle
Bronchial arteries and veins
Bronchi and large bronchioles receive blood supply from the systemic circulation.
Bronchial aa arise from the aorta or posterior intercostal a.
Bronchial veins drain into the azygous system and pulmonary veins.
Lymphatics of the lung.
Pulmonary (intrapulmonary) lymphatics have a diffuse distrivution, they drain into the hilar (bronchopulmonary) nodes --> carinal (inferior tracheobronchial) nodes --> superior tracheoronchial nodes --> tracheal (paratracheal) nodes --> bronchomediastinal lymph trunks to the right lymph duct or thoracic duct or directly into the brachiocephalic vein (R/L). May also drain to inferior deep cervical nodes.
The left lower lobe drains to carinal nodes, then predominanly across the midline to the right paratracheal nodes.
Efferent innervation of lungs
Parasympathetic: vagus (CN X).
Preganglionic cell bodies are located in the medulla of the brainstem. Ganglia are intramural - within lungs, trachea.
Actions: bronchoconstriction, vasodilation, secretomotor to glands of bronchial tree.
Preganglionics in T1-T5 spinal cord, synapse in sympathetic chain, postganglionic axons travel through pulmonary plexus located anterior and posterior to primary bronchi.
Actions: bronchodilator, vasocontrictor, inhibits gland of bronchial tree.
Afferent innervation of lungs
- Stretch, irritants: travel with vagus n to brainstem (neuron cell bodies in inferior ganglion of vagus n), pressure receptors in pulmonary aa and chemoreceptors in pulmonary vv also travel via the vagus.
- Pain (nociceptive): travel with sympathetics to T1-T5 spinal cord, except via dorsal root (neuron cell bodies in dorsal root ganglia of T1-T5). The exception is the trachea which travels via the vagus.
Surface anatomy apex
1-2 cm above medial 1/3 of clavicle
Surface anatom of anterior border
Deep to sternum, except cardiac notch on left (ribs 4-6)
Surface anatomy inferior border