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Lungs By James Gallagher, kindly presented by Aaron CampbellLearning outcomes • Identify and describe the anatomy of the trachea and bronchial tree • Identify and describe the fissures, lobes, borders and surfaces of the right and left lungs • Identify the hilar structures of the right and left lungs • Identify and describe the surface projections of the right and left lungs • Identify and describe the anatomy of the diaphragm in terms of location, attachments, function, innervation and openings • Identify and describe the azygos system of veins • Identify and describe the anatomy and course of the thoracic duct • Identify and describe the sympathetic chain • Identify the normal anatomy of the thoracic cavity on plain film x -ray images Trachea • C-shaped cartilage rings with trachealis muscle at post aspect • Begins at level of C6 (lower border of cricoid cartilage) • Ant. to oesophagus • Bifurcates at T4 level (Carina) to give L and R main bronchi • Only present in sup. Mediastinum • Lined by ciliated pseudostratified columnar epi. and goblet cells • Sensory innervation= recurrent laryngeal n. • Art. Supply= inferior thyroid a. Bronchi • Primary bronchi formed at level of sternal angle • Further bifurcation forms secondary bronchi (3 right, 2 left) which supply lobes • Secondary split to form segmental bronchi (supply bronchopulmonary segments) • Right main bronchus= wider, shorter, more vertical (higher risk of foreign body inhalation) • Left main bronchus= inf to aortic arch, ant to thoracic aorta • Cartilage encircles lumen in both main bronchi • Lobar and segmantal bronchi= cresent shaped cartilage • Nerve supply= vagus nerve • Blood supply= bronchial a./v. Bronchioles • No cartilage/ goblet cells • Club cells produce surfactant= prevents walls sticking together in expiration • Conducting bronchioles -> terminal bronchioles - > terminal bronchioles -> respiratory bronchioles -> alveoli Asthma • Asthma is a chronic inflammatory disorder of the airways, characterised by hypersensitivity, reversible outflow obstruction and bronchospasm. • There is remodelling of the small airways, causing increased smooth muscle thickness around the bronchioles, damaged epithelium and a thickened basement membrane. • “Asthma attacks” are acute exacerbations of the condition whereby a trigger (e.g. allergens, exercise) causes sudden inflammation and contraction of the smooth muscle around bronchioles (bronchospasm). This narrows the airways, causing difficulty in breathing and wheezing, a characteristic feature of asthma.Lung Structure • Cone shaped, left smaller than right due to presence of heart • Each lung consists of: • Apex – The blunt superior end of the lung. It projects upwards, above the level of the 1st rib and into the floor of the neck. • Base – The inferior surface of the lung, which sits on the diaphragm. • Lobes (two or three) – These are separated by fissures within the lung. • Surfaces (three) – These correspond to the area of the thorax that they face. They are named costal, mediastinal and diaphragmatic. • Borders (three) – The edges of the lungs, named the anterior, inferior and posterior borders. Lobes • The right lung has three lobes; superior, middle and inferior. The lobes are divided from each other by two fissures: • Oblique fissure – Runs from the inferior border of the lung in a superoposterior direction, until it meets the posterior lung border. • Horizontal fissure– Runs horizontally from the sternum, at the level of the 4th rib, to meet the oblique fissure. • The left lung contains superior and inferior lobes, which are separated by a similar oblique fissure.Surfaces • The mediastinal surface of the lung faces the lateral aspect of the middle mediastinum. The lung hilum (where structures enter and leave the lung) is located on this surface. • The base of the lung is formed by the diaphragmatic surface. It rests on the dome of the diaphragm, and has a concave shape. This concavity is deeper in the right lung, due to the higher position of the right dome overlying the liver. • The costal surface is smooth and convex. It faces the internal surface of the chest wall. It is related to the costal pleura, which separates it from the ribs and innermost intercostal muscles. Mediastinal impressions • Mediastinal surfaces contain a number of impressions: Left Lung Right Lung •Heart •Oesophagus •Arch of aorta •Heart •Inferior vena cava •Thoracic aorta •Superior vena •Oesophagus cava •Subclavian a. •Azygous vein *right impressions= venous, left impressions= arterial Borders • The anterior border of the lung is formed by the convergence of the mediastinal and costal surfaces. On the left lung, the anterior border is marked by a deep notch, created by the apex of the heart. It is known as the cardiac notch. • The inferior border separates the base of the lung from the costal and mediastinal surfaces. • The posterior border is smooth and rounded (in contrast to the anterior and inferior borders, which are sharp). It is formed by the costal and mediastinal surfaces meeting posteriorly. Roots • The lung root is a collection of structures that suspends the lung from the mediastinum. Each root contains a bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, pulmonary plexus of nerves and lymphatic vessels. • All these structures enter or leave the lung via the hilum – a wedge shaped area on its mediastinal surface. Vasculature • The lungs are supplied with deoxygenated blood by the paired pulmonary arteries. Once the blood has received oxygenation, it leaves the lungs via four pulmonary veins (two for each lung). • The bronchi, lung roots, visceral pleura and supporting lung tissues require an extra nutritive blood supply. This is delivered by the bronchial arteries, which arise from the descending aorta. • The bronchial veins provide venous drainage. The right bronchial vein drains into the azygos vein, whilst the left drains into the accessory hemiazygos vein. Nerves and lymphatics • The nerves of the lungs are derived from the pulmonary plexuses. They feature sympathetic, parasympathetic and visceral afferent fibres: • Parasympathetic – derived from the vagus nerve. They stimulate secretion from the bronchial glands, contraction of the bronchial smooth muscle, and vasodilation of the pulmonary vessels. • Sympathetic – derived from the sympathetic trunks. They stimulate relaxation of the bronchial smooth muscle, and vasoconstriction of the pulmonary vessels. • Visceral afferent – conduct pain impulses to the sensory ganglion of the vagus nerve. • The lymphatic vessels of the lung arise from two lymphatic plexuses: • Superficial (subpleural) – drains the lung parenchyma. • Deep – drains the structures of the lung root. • Both these plexuses empty into the trachebronchial nodes – located around the bifurcation of the trachea and the main bronchi. From here, lymph passes into the right and left bronchomediastinal trunks. Which blood tests might Pulmonary embolism you request for suspected • A pulmonary embolism refers to the obstruction of a PE? pulmonary artery by a substance that has travelled from elsewhere in the body. The most common emboli are: • Thrombus – responsible for the majority of cases and usually arises in a distant vein. • Fat – following a bone fracture or orthopaedic surgery. • Air – following cannulation in the neck. • The effect of a pulmonary embolism is a reduction in lung perfusion. This results in decreased blood oxygenation, and the accumulation of blood in the right ventricle of the heart. haemoptysis and tachypnoea. In clinical medicine, the Wells’ score is used to assess the probability of PE. • Definitive treatment involves anticoagulation and thrombolytic therapy. This reduces the size of the embolus, and prevents further clotting. Diaphragm • The diaphragm is located at the inferior -most aspect of the ribcage, filling the inferior thoracic aperture. It acts as the floor of the thoracic cavity and the roof of the abdominal cavity. The attachments of diaphragm can be divided into peripheral and central attachments. It has three peripheral attachments: • Lumbar vertebrae and arcuate ligaments. • Costal cartilages of ribs 7 -10 (attach directly to ribs 11-12). • Xiphoid process of the sternum . • The parts of the diaphragm that arise from the vertebrae are tendinous in structure, and are known as the right and left crura: • Right crus – Arises from L1-L3 and their intervertebral discs. Some fibres from the right crus surround the oesophageal opening, acting as a physiological sphincter to prevent reflux of gastric contents into the oesophagus. • Left crus – Arises from L1-L2 and their intervertebral discs . • The muscle fibres of the diaphragm combine to form a central tendon. This tendon ascends to fuse with the inferior surface of the fibrous pericardium. Either side of the pericardium, the diaphragm ascends to form left and right domes. At rest, the right dome lies slightly higher than the left – this is thought to be due to the presence of the liver. Openings Oesophageal Aortic Hiatus Caval Hiatus (T8) Hiatus (T10) (T12) •Oesophagus •Inferior vena cava •Right and left •Aorta •Terminal branches vagus nerves •Thoracic duct of right phrenic •Oesophageal nerve branches of left •Azygous vein gastric artery/vein A tip for remembering the vertebral levels: vena cava has eight letters (T8), oesophagus has ten letters (T10), and aortic hiatus has twelve letters (T12). Neurovasculature • The halves of the diaphragm receive motor innervation from the phrenic nerve. The left half of the diaphragm (known as a hemidiaphragm) is innervated by the left phrenic nerve, and vice versa. Each phrenic nerve is formed in the neck within the cervical plexus and contains fibres from spinal roots C3-C5. • The majority of the arterial supply to the diaphragm is delivered via the inferior phrenic arteries, which arise directly from the abdominal aorta. The remaining supply is from the superior phrenic, pericardiacophrenic, and musculophrenic arteries. The draining veins follow the aforementioned arteries.Paralysis of diaphragm • Caused by damage to phrenic nerve, cervical spinal cord or brainstem due to: • Mechanical trauma: ligation or damage to the nerve during surgery. • Compression: due to a tumour within the chest cavity. • Myopathies: such as myasthenia gravis. • Neuropathies: such diabetic neuropathy. • Paralysis of the diaphragm produces a paradoxical movement. The affected side of the diaphragm moves upwards during inspiration, and downwards during expiration. A unilateral diaphragmatic paralysis is usually asymptomatic and is most often an incidental finding on x -ray. If both sides are paralysed, the patient may experience poor exercise tolerance, orthopnoea and fatigue. Lung function tests will show a restrictive deficit. • Management of diaphragmatic paralysis is two -fold. Firstly, the underlying cause must be identified and treated. The second part of treatment deals with symptomatic relief. This is usually via non-invasive ventilation, such as a CPAP (continuous positive airway pressure) machine Thoracic duct • Largest lymphatic channel (lymph from everywhere but upper right quadrant to venous system) • Originates at L1 at cisterna chyli (in abdomen) • Ascends through aortic hiatus • Passes between oesophagus and vertabrae in middle • Moves to left as enters superior mediastinum • Receives branches along course, including jugular, subclavian and broncho-mediastinal trunks near its termination • Terminates at union of L. jugular and subclavian v. (left venus angle) Sympathetic trunks • Sympathetic fibres from sympathetic ganglions innervate visceral structures of thorax and abdomen • Fibres descend along posterior aspect, moving medially as descend • T1-T4 innervate thoracic viscera • T5-T9/10 form greater splanchnic nerve • T9/10-T11 form lesser splanchnic nerve • T12 forms least splanchnic nerve Phrenic Nerves • “C3,C4,C5 keep the diaphragm alive” • Supply diaphragm, pericardium and mediastinal pleura • Right: Descends along right brachiocephalic v., SVC and pericardium – Ant. to root of right lung – Right of IVC and passes through diaphragm near caval opening • Left: Descends between L. subclavian and left common carotid – Ant. to arch of aorta – Ant. to left lung root – Through diaphragm to left of pericardium, giving fibres on inferior surface of diaphragm.Azygous System of Veins • Azygous v – Drains right post thorax (and abdomen) – Formed from r. ascending lumbar and subcostal v. – Ascends post. mediastinum close to T5-12 vertebrae – Arches over root of right lung to terminate in SVC – Drains 2 ndto 12thright intercostal v., mediastinal, oesophageal and bronchial v. • Hemi-Azygous v. – Arises from left lumbar v. – Ascends on vertebral bodies of T12 to T8/9. – Crosses at T8/9 to join azygous v. on right side. – Receives intercostal v. 9-11, communicates with L. renal v. • Accessory Hemi-azygous v. – Medial aspect of 4 thIntercostal space to T8 on left – Receives 4 thto 8thintercostal v. (and sometimes left bronchial v.) – Crosses at T8 to join azygous on right (may join directly to hemi-azygous)Normal Chest X-rayIdentify the pathology• Is this feature pathological?