Volume 1, BD Chaurasia Human Anatomy, Upper Limb and Thorax PDF

THORAX 264 16 Lungs One thousand Americans and same number of Indians stop smoking everyday – by dying ...

THORAX 264 16 Lungs One thousand Americans and same number of Indians stop smoking everyday – by dying  —Anonymous INTRODUCTION plexus. The pulmonary artery lies above the bronchus. The lungs occupying major portions of the thoracic Anterior to the bronchus is the upper pulmonary vein, while cavity, leave little space for the heart, which excavates the lower vein lies below the bronchus. more of the left lung. The two lungs hold the heart tight The mediastinal surface of left lung has the between them, providing it the protection, it rightly impression of left ventricle, ascending aorta. Behind the deserves. There are ten bronchopulmonary segments root of the left lung are the impressions of descending in each lung. thoracic aorta while oesophagus leaves an impression The lungs are a pair of respiratory organs situated in the lower part only (Refer to BDC App). in the thoracic cavity. Each lung invaginates the corresponding pleural cavity. The right and left lungs LUNGS are separated by the mediastinum. Features The lungs are spongy in texture. In the young, the Each lung is conical in shape (Fig. 16.1). It has: lungs are brown or grey in colour. Gradually, they 1 An apex at the upper end. become mottled black because of the deposition of 2 A base resting on the diaphragm. inhaled carbon particles. The right lung weighs about 3 Three borders, i.e. anterior, posterior and inferior. 700 g; it is about 50 to 100 g heavier than the left lung. 4 Two surfaces, i.e. costal and medial. The medial surface is divided into vertebral and mediastinal parts. DISSECTION The apex is blunt and lies above the level of the Identify the lungs by the thin anterior border, thick anterior end of the first rib. It reaches nearly 2.5 cm posterior border, conical apex, wider base, medial surface above the medial one-third of the clavicle, just medial with hilum and costal surface with impressions of the to the supraclavicular fossa. It is covered by the cervical ribs and intercostal spaces. In addition, the right lung is pleura, the suprapleural membrane, and is grooved by distinguished by the presence of three lobes, whereas the subclavian artery on the medial side and anteriorly Thorax left lung comprises two lobes only (refer to BDC App). (see Fig. 12.10). On the mediastinal part of the medial surface of right The base is semilunar and concave. It rests on the lung identify two bronchi—the eparterial and hyparterial diaphragm which separates the right lung from the bronchi, with bronchial vessels and posterior pulmonary right lobe of the liver, and the left lung from the left plexus, the pulmonary artery between the two bronchi lobe of the liver, the fundus of the stomach, and the on an anterior plane. The upper pulmonary vein is spleen (see Fig. 15.8). situated still on an anterior plane while the lower The anterior border is very thin (Figs 16.2 and 16.3). It pulmonary vein is identified below the bronchi. is shorter than the posterior border. On the right side, 2 The impressions on the right lung in front of root of it is vertical and corresponds to the anterior or Section lung are of superior vena cava, inferior vena cava, and costomediastinal line of pleural reflection. The anterior right ventricle. The impressions behind the root of lung border of the left lung shows a wide cardiac notch below are those of vena azygos and oesophagus (Table 16.1). the level of the fourth costal cartilage. The heart and Hilum of the left lung shows the single bronchus situated pericardium are not covered by the lung in the region posteriorly, with bronchial vessels and posterior pulmonary of this notch. 264  LUNGS 265 Fissures and Lobes of the Lungs The right lung is divided into three lobes (upper, middle and lower) by two fissures (oblique and horizontal). The left lung is divided into two lobes by the oblique fissure (Fig. 16.1a). The oblique fissure cuts into the whole thickness of the lung, except at the hilum. It passes obliquely downwards and forwards, crossing the posterior border about 6 cm below the apex and the inferior border about 5 cm from the median plane. Due to the oblique plane of the fissure, the lower lobe is more posterior and the upper and middle lobes more anterior. In the right lung, the horizontal fissure passes from the anterior border up to the oblique fissure and separates a wedge-shaped middle lobe from the upper Fig. 16.1a: The trachea and lungs as seen from the front lobe. The fissure runs horizontally at the level of the fourth costal cartilage and meets the oblique fissure in The posterior border is thick and ill defined. It the midaxillary line. corresponds to the medial margins of the heads of the The tongue-shaped projection of the left lung below ribs. It extends from the level of the seventh cervical the cardiac notch is called the lingula. It corresponds to spine to the tenth thoracic spine. the middle lobe of the right lung. The inferior border separates the base from the costal The lungs expand maximally in the inferior direction and medial surfaces. because movements of the thoracic wall and diaphragm The costal surface is large and convex. It is in contact are maximal towards the base of the lung. The presence with the costal pleura and the overlying thoracic wall. of the oblique fissure of each lung allows a more The medial surface is divided into a posterior or uniform expansion of the whole lung. vertebral part, and an anterior or mediastinal part. The vertebral part is related to the vertebral bodies, Surface Marking of the Lung intervertebral discs, the posterior intercostal vessels and Surface marking of lung is same as that of visceral pleura the splanchnic nerves (see Figs 15.2 and 15.3). The described in Chapter 15. The surface marking of oblique mediastinal part is related to the mediastinal septum, and horizontal fissures is mentioned here. and shows a cardiac impression, the hilum and a The oblique fissure can be drawn by joining: number of other impressions which differ on the two a. A point 2 cm lateral to the third thoracic spine. sides. Various relations of the mediastinal surfaces of b. Another point on the fifth rib in the midaxillary the two lungs are listed in Table 16.1. line (see Fig. 15.4). Thorax 2Section Fig. 16.1b: Trachea, lungs and heart as seen from the front  THORAX 266 Fig. 16.2: Impressions on the mediastinal surface of the right lung Thorax 2 Section Fig. 16.3: Impressions on the mediastinal surface of the left lung  LUNGS 267 Table 16.1: Structures related to the mediastinal Arrangement of Structures in the Root surfaces of the right and left lungs Right side: From posterior to anterior side: Right side (Fig.16.2) Left side (Fig.16.3) 1. Eparterial bronchus, hyparterial bronchus with 1. Right atrium and auricle 1. Left ventricle, left auricle, bronchial vessels and posterior pulmonary plexus infundibulum and adjoining along their posterior walls (Figs 16.4a and b). part of the right ventricle 2. Pulmonary artery in midplane between the two bronchi. 2. A small part of the right 2. Pulmonary trunk 3. Superior and inferior pulmonary veins in anterior part. ventricle 4. Anterior pulmonary plexus, lymph nodes and lymph 3. Superior vena cava 3. Arch of aorta vessels in the anterior and inferior parts. 4. Lower part of the right 4. Descending thoracic aorta Left side: From posterior to anterior side: brachiocephalic vein 1. Single bronchus with bronchial vessels and posterior 5. Azygos vein 5. Left subclavian artery pulmonary plexus along its posterior wall. 6. Oesophagus 6. Thoracic duct 2. Pulmonary artery in middle area placed above the 7. Inferior vena cava 7. Oesophagus bronchus (Figs 16.4a and b). 8. Trachea 8. Left brachiocephalic vein 3. Superior and inferior pulmonary veins in anterior part. 9. Right vagus nerve 9. Left vagus nerve 4. Anterior pulmonary plexus, lymph nodes and lymph 10.Right phrenic nerve 10. Left phrenic nerve vessels in the anterior and inferior parts. 11. Left recurrent laryngeal nerve Relations of the Root c. A third point on the sixth costal cartilage 7.5 cm from the median plane. Anterior 1 Common on the two sides: The horizontal fissure is represented by a line joining: a. Phrenic nerve a. A point on the anterior border of the right lung at b. Pericardiacophrenic vessels the level of the fourth costal cartilage. c. Anterior pulmonary plexus b. A second point on the fifth rib in the midaxillary line. 2 On the right side: Competency achievement: The student should be able to: a. Superior vena cava (Fig. 16.2) AN 24.2 Identify side, external features and relations of structures b. A part of the right atrium. which form root of lung and bronchial tree and their clinical Posterior correlate.1 1 Common on the two sides: Root of the Lung a. Vagus nerve b. Posterior pulmonary plexus Root of the lung is a short, broad pedicle which connects 2 On left side: Descending thoracic aorta the medial surface of the lung to the mediastinum. It is formed by structures which either enter or come out of Superior the lung at the hilum (Latin depression). The roots of 1 On right side: Terminal part of azygos vein the lungs lie opposite the bodies of the fifth, sixth and 2 On left side: Arch of the aorta. seventh thoracic vertebrae. Inferior Contents Pulmonary ligament. The root is made up of the following structures. Thorax Differences between the Right and Left Lungs 1 Principal bronchus on the left side, and eparterial and hyparterial bronchi on the right side in posterior part. Differences between right and left lungs are given in Table 16.2. 2 One pulmonary artery in middle part. 3 Two pulmonary veins, superior and inferior, in Competency achievement: The student should be able to: anterior part (Figs 16.4a and b). AN 24.5 Mention the blood supply, lymphatic drainage and nerve 4 Bronchial arteries—one on the right side and two on supply of lungs.2 2 the left side. Arterial Supply Section 5 Bronchial veins 6 Anterior and posterior pulmonary plexuses of nerves The bronchial arteries supply nutrition to the bronchial 7 Lymphatics of the lung tree and to the pulmonary tissue. These are small 8 Bronchopulmonary lymph nodes arteries that vary in number, size and origin, but usually 9 Areolar tissue they are as follows:  THORAX 268 Table 16.2: Differences between the right and left lungs 1 On the right side, there is one bronchial artery Right lung (Fig. 16.4a) Left lung which arises from the third right posterior inter- costal artery. 1. Shorter and broader 1. Longer and narrower 2 On the left side, there are two bronchial arteries, both 2. Larger and heavier, 2. Smaller and lighter, weighs of which arise from the descending thoracic aorta, weighs about 700 g about 600 g the upper opposite fifth thoracic vertebra and the lower just below the left bronchus. 3. Anterior border is 3. Anterior border is interrupted straight by the cardiac notch Deoxygenated blood is brought to the lungs by the two pulmonary arteries and oxygenated blood is 4. Cardiac impression 4. Cardiac impression deep returned to the heart by the four pulmonary veins. shallow/absent There are precapillary anastomoses between 5. Absence of lingula 5. Lingula present bronchial and pulmonary arteries. These connections 6. It has 2 fissures and 6. It has only one fissure and enlarge when any one of them is obstructed in 3 lobes 2 lobes disease. Fig. 16.4a: Roots of the right and left lungs Thorax 2 Section Fig. 16.4b: Gross anatomy of lungs including their roots  LUNGS 269 Venous Drainage of the Lungs BRONCHIAL TREE The venous blood from the first and second divisions of the bronchi is carried by bronchial veins. Usually Features there are two bronchial veins on each side. The right The trachea divides at the level of the lower border of bronchial veins drain into the azygos vein. The left the fourth thoracic vertebra into two primary principal bronchial veins drain into the hemiazygos vein. bronchi, one for each lung. The right principal bronchus The greater part of the venous blood from the lungs is 2.5 cm long. It is shorter, wider and more in line with is drained by the pulmonary veins. the trachea than the left principal bronchus (Fig. 16.5a). Inhaled particles or foreign bodies, therefore, tend to Lymphatic Drainage pass more frequently to the right lung, with the result There are two sets of lymphatics, both of which drain that infections are more common on the right side than into the bronchopulmonary nodes. on the left. 1 Superficial vessels drain the peripheral lung tissue The left principal bronchus is 5 cm. It is longer, lying beneath the pulmonary pleura. The vessels pass narrower and more oblique than the right bronchus. round the borders of the lung and margins of the Right bronchus makes an angle of 25° with tracheal fissures to reach the hilum. bifurcation, while left bronchus makes an angle of 45° with the trachea. 2 Deep lymphatics drain the bronchial tree, the Each principal bronchus enters the lung through the pulmonary vessels and the connective tissue septa. hilum, and divides into secondary lobar bronchi, one for They run towards the hilum where they drain into each lobe of the lungs. Thus there are three lobar the bronchopulmonary nodes (Fig. 16.4a). bronchi on the right side, and only two on the left The superficial vessels have numerous valves and side. Each lobar bronchus divides into tertiary or the deep vessels have only a few valves or no valves at segmental bronchi, one for each bronchopulmonary all. Though there is no free anastomosis between the segment; which are 10 on the right side and 10 on the superficial and deep vessels, some connections exist left side. The segmental bronchi divide repeatedly to which can open up, so that lymph can flow from the form very small branches called terminal bronchioles. deep to the superficial lymphatics when the deep Still smaller branches are called respiratory bronchioles vessels are obstructed in disease of the lungs or of the (Fig. 16.6). lymph nodes. Each respiratory bronchiole aerates a small part of the lung known as a pulmonary unit. The respiratory Nerve Supply bronchiole ends in microscopic passages which are termed: 1 Parasympathetic nerves are derived from the vagus. 1 Alveolar ducts (Fig. 16.7) These fibres are: 2 Atria a. Motor to the bronchial muscles, and on stimul- 3 Air saccules ation cause bronchospasm. 4 Pulmonary alveoli (Latin small cavity). Gaseous b. Secretomotor to the mucous glands of the exchanges take place in the alveoli. bronchial tree. c. Sensory fibres are responsible for the stretch reflex DISSECTION of the lungs, and for the cough reflex. Dissect the principal bronchus into the left lung. Remove Thorax 2 Sympathetic nerves are derived from second to fifth the pulmonary tissue and follow the main bronchus till sympathetic ganglia. These are inhibitory to the it is seen to divide into two lobar bronchi. Try to dissect smooth muscle and glands of the bronchial tree. That till these divide into the segmental bronchi (Fig. 16.5a). is how sympathomimetic drugs, like adrenaline, cause Dissect the principal bronchus into the right lung. bronchodilatation and relieve symptoms of bronchial Remove the pulmonary tissue and follow the main asthma. bronchus till it is seen to divide into three lobar bronchi. Both parasympathetic and sympathetic nerves first Try to dissect till these divide into segmental bronchi. 2 form anterior and posterior pulmonary plexuses Section situated in front of and behind the lung roots: From Competency achievement: The student should be able to: the plexuses, nerves are distributed to the lungs along AN 24.3 Describe a bronchopulmonary segment.3 the blood vessels and bronchi (Fig. 16.4).  THORAX 270 Figs 16.5a–c: Bronchopulmonary segments of the lungs (both sides 1 to 10, see Table 16.3). Medial basal segments are not seen in (b) and (c). Table 16.3: The bronchopulmonary segments Right lung Bronchopulmonary Segments Lobes Segments The most widely accepted classification of segments is A. Upper 1. Apical given in Table 16.3. There are 10 segments on the right 2. Posterior side and 10 on the left side (Figs 16.5a–c and 16.8 a and b). 3. Anterior B. Middle 4. Lateral Definition 5. Medial C. Lower 6. Superior Bronchopulmonary segments are well-defined 7. Medial basal anatomical segments aerated by tertiary/segmental Thorax 8. Anterior basal bronchus. These are pyramidal in shape with apex 9. Lateral basal directed towards hilum and base directed towards 10. Posterior basal periphery having their own arterial supply; but venous Left lung drainage is shared by adjacent bronchopulmonary A. Upper 1. Apical segment. Upper division 2. Posterior 3. Anterior Features Lower division 4. Superior lingular 2 1 These are well-defined anatomic, functional and 5. Inferior lingular surgical sectors of the lung. Section B. Lower 6. Superior 2 Each one is aerated by a tertiary or segmental 7. Medial basal bronchus. 8. Anterior basal 9. Lateral basal 3 Each segment is pyramidal in shape with its apex 10. Posterior basal directed towards the root of the lung (Fig. 16.8).  LUNGS 271 Fig. 16.7: Parts of a pulmonary unit Fig. 16.6: Bronchial tree Thorax 2Section Figs 16.8a and b: The bronchopulmonary segments as seen on: (a) The costal aspects of the right and left lungs. Medial basal segments (no. 7) are not seen, and (b) segments seen on the medial surface of left and right lungs. Lateral segment of middle lobe (no. 4) is not seen on right side  THORAX 272 4 Each segment has a segmental bronchus, segmental epithelial lining of the respiratory system is artery, autonomic nerves and lymph vessels. endodermal in origin. It forms the lining of the larynx, 5 The segmental venules lies in the connective tissue the trachea, the bronchi and the pulmonary alveoli. between adjacent pulmonary units of bronchopul- The connective tissue, cartilage and smooth muscles monary segments. of these structures develop from splanchnic 6 During segmental resection, the surgeon works mesenchyme surrounding the foregut. As develop- along the segmental veins to isolate a particular ment progresses, the diverticulum separates from the segment. foregut by the tracheo-oesophageal septum (except at the entrance to the larynx). Relation to Pulmonary Artery The respiratory diverticulum below the larynx grows The branches of the pulmonary artery accompany the caudally and forms the trachea in the midline. This bronchi. The artery lies dorsolateral to the bronchus. bifurcates into two lateral outpocketings; the lung buds. Thus each segment has its own separate artery In the fifth week of intrauterine life, the proximal parts (Fig. 16.9). of each lung bud forms the principal bronchi. Each of these grows laterally and invaginates the pericardio- Relation to Pulmonary Vein peritoneal canals (primitive pleural cavities). Following The pulmonary veins do not accompany the bronchi this, the primary bronchi divide into secondary bronchi or pulmonary arteries. They run in the intersegmental (3 on the right side and 2 on the left side). These divide planes. Thus each segment has more than one vein and dichotomously into tertiary bronchi. Each tertiary each vein drains more than one segment. Near the bronchus with its surrounding mesenchyme forms a hilum, the veins are ventromedial to the bronchus. bronchopulmonary segment. By 24th week, about 17 It should be noted that the bronchopulmonary orders of branches are formed and the lung parenchyma segment is not a bronchovascular segment because it develops in four stages. does not have its own vein. 1 Pseudoglandular stage (between 5 and 17 weeks). In this stage, developing lung resembles a gland. Competency achievement: The student should be able to: 2 Canalicular stage (between 16 and 25 weeks), the AN 25.2 Describe development of pleura, lung and heart.4 lumina of bronchi and bronchioles become larger and tissue becomes more vascular. DEVELOPMENT OF RESPIRATORY SYSTEM 3 Terminal sac stage (between 24 weeks to birth). Many saccules appear at the ends of terminal bronchioles The lower respiratory tract primordium appears in the (terminal sacs). Capillaries bulge into these sacs. third week of intrauterine life in the form of an 4 Alveolar stage (late fetal period to 8 years after birth). outgrowth (respiratory diverticulum) from the ventral The epithelial lining of the sacs becomes an extremely wall of the primitive pharynx, i.e. the part of the thin squamous layer and the alveolocapillary foregut caudal to the hypobranchial eminence. Hence membrane allows exchange of gases. The four stages overlap each other because the cranial segments of the lungs mature faster than the caudal ones. By 28–32 weeks, some of the alveolar epithelial cells secrete a substance which is capable of lowering the surface tension at the air–alveolar interface and thus Thorax helps maintaining the patency of the alveoli; this is known as pulmonary surfactant. Table 16.4 and Flowchart 16.1 show the development of respiratory system. Molecular Regulation 1. Transcription factor (TBX4) expressed in the 2 endoderm of gut tube at the site of respiratory Section diverticulum induces formation of lung bud and is responsible for growth and differentiation of lungs. 2. Fibroblast growth factor 10 (FGF10) and other signals Fig. 16.9: Distal portions of adjacent bronchopulmonary from splanchnic mesenchyme probably induces the segments outgrowth of tracheal bud.  LUNGS 273 Table 16.4: Development of components of respiratory system S. no. Component Developed from 1 Epithelium of larynx, trachea, bronchi and alveoli Endoderm of foregut 2 Muscles of larynx Branchial mesoderm of IVth and VIth arches 3 Cartilages of larynx IV arch cartilage Thyroid VI arch cartilage Cricoid Arytenoid 4 Epiglottis Dorsal part of hypobranchial eminence (fused ventral part of III and IV arches) 5 Glands of respiratory tract Endoderm 6 Muscles, cartilages and connective tissue of trachea and bronchi Splanchnic mesoderm Flowchart 16.1: Quick review of sequence of development of Congenital Anomalies respiratory system 1 Tracheo-oesophageal fistula: This abnormal communication between the trachea and the oesophagus is due to a deviation of the oesophago- tracheal septum or from mechanical factor pushing the dorsal wall of the foregut anteriorly. 2 Tracheal stenosis 3 Azygos lobe of lung around vena azygos: This may be due to an additional respiratory bud which develops independently of the main respiratory system. 4 Hyaline membrane disease or distress syndrome: This is due to a deficiency of pulmonary surfactant. 5 Agenesis of lung. HISTOLOGY In a section of the lung, the mesothelial covering of visceral pleura may be visible. The structure of the lung is a lacework of alveoli separated by thin-walled septa. This is traversed by system of intrapulmonary bronchi, bronchioles and alveolar ducts, into which atria, alveolar sacs and alveoli open. Intrapulmonary Bronchus Intrapulmonary bronchus is lined by pseudostratified ciliated columnar epithelium with goblet cells resting on a thin basement membrane. Cilia prevent the Thorax accumulation of mucus in the bronchial tree. The lamina propria consists of reticular and elastic fibres. The submucous coat contains both mucous and serous acini. A complete layer of smooth muscle fibres is present which is responsible for infoldings of the mucous membrane. Outermost is the hyaline cartilage which is visible as small cartilaginous plates of varying 2 sizes and shapes (Fig. 16.10) with tunica adventitia. Section Terminal bronchiole is part of the conducting system 3. Sonic hedgehog (SHH-GLi) and other signaling of respiratory pathway which is less than 1 mm in molecules are involved in the epithelial mesenchyme diameter. It is lined by simple columnar epithelium. The interaction which governs the branching of tracheal lamina propria contains elastic and smooth muscle fibres. bud and its proliferation. Both the glands and cartilage plates are absent (Fig. 16.11).  THORAX 274 membrane. The main support of the alveoli is provided by elastic fibres. Majority of cells lining the alveoli are the squamous cells or type I pneumocytes. A few cells are larger cells or type II pneumocytes. Type II cells secrete the surfactant which lowers surface tension and prevents alveoli from collapsing. The interalveolar septum containing numerous capillaries lined by continuous non-fenestrated endothelial cells is present between the adjacent alveoli. CLINICAL ANATOMY Usually, the infection of a bronchopulmonary segment remains restricted to it, although tuberculosis and bronchogenic carcinoma may spread from one segment to another. Knowledge of the detailed anatomy of the bronchial tree helps considerably in: Fig. 16.10: Intrapulmonary bronchus a. Segmental resection (Fig. 16.12). b. Visualising the interior of the bronchi through a bronchoscope passed through the mouth and trachea. The procedure is called bronchoscopy. Carina is a hook-shaped process projecting backwards from the lower margin of lowest tracheal ring. It helps to divide trachea into two primary bronchi. Right bronchus makes an angle of 25°, while left one makes an angle of 45°. Foreign bodies mostly descend into right bronchus (Fig. 16.13) as it is wider and more vertical than the left bronchus. Enlarged lymph nodes present in this area may distort the carina. Carina (Latin keel) of the trachea is a sensitive area. When patient is made to lie on her/his left side, secretions from right bronchial tree flow towards the carina due to effect of gravity. This stimulates the cough reflex, and sputum is brought out. This is called postural drainage (Fig. 16.14). Thorax Fig. 16.11: Structure of terminal bronchiole Respiratory Bronchiole Respiratory bronchiole is lined by cuboidal epithelium. The walls consist of collagenous connective tissue containing bundles of interlacing smooth muscle fibres and elastic fibres. At number of places, the alveolar sacs and alveoli arise from the respiratory bronchiole and 2 its cuboidal epithelium is continuous with the Section squamous epithelium of alveolar sacs and alveoli. Alveoli Alveoli are thin-walled polyhedral sacs. The alveoli are Fig. 16.12: Segmental resection lined by two types of cells, which rest on a basement  LUNGS 275 Bronchial asthma is a common disease of res- piratory system. It occurs due to bronchospasm of smooth muscles in the wall of bronchioles. Patient has difficulty especially during expiration. It is accompanied by wheezing. Epinephrine, a sympathomimetic drug, relieves the symptoms. Auscultation of lung: Upper lobe is auscultated above 4th rib on both sides; lower lobes are best heard on the back. Middle lobe is auscultated between 4th and 6th ribs on right side. Superior segment of lower lobe is the most depen- dent bronchopulmonary segment in supine position. Foreign bodies are likely to be lodged here. Mnemonics Bronchopulmonary segments of right lung Fig. 16.13: Angles of right and left bronchi with carina “A PALM Seed Makes Another Little Palm”. In order from superior to inferior: Apical Posterior Anterior Lateral Medial Superior Medial basal Anterior basal Lateral basal Fig. 16.14: Postural drainage from right lung Posterior basal Lung lobes: One having lingula, lobe numbers Paradoxical respiration: During inspiration, Lingula is on Left the flail (abnormally mobile) segments of ribs are pulled inside the chest wall while during expira- The lingula is like an atrophied lobe, so the left lung tion the ribs are pushed out (Fig. 16.15). must have two "other" lobes, and, therefore, right lung has three lobes. Tuberculosis of lung is one of the commonest diseases. A complete course of treatment must be taken under the guidance of a physician. FACTS TO REMEMBER Large spongy lungs occupy almost whole of Thorax thoracic cage leaving little space for the heart and accompanying blood vessels, etc. Bronchopulmonary segments are independent functional units of lung. Lungs are subjected to lot of insult by the smoke of cigarette/bidis/pollution. Tuberculosis of lung is one of the commonest killer 2 in an underdeveloped or a developing country. Section Complete treatment of TB is a must, otherwise the bacteria become resistant to antitubercular treatment. People harbouring resistant bacteria spread the Fig. 16.15: Paradoxical respiration disease to people around through their sputum.  THORAX 276 CLINICOANATOMICAL PROBLEMS Ans: The bronchogenic carcinoma spreads to the bronchomediastinal lymph nodes. The left supra- Case 1 clavicular nodes are also enlarged and palpable; so A young boy with sore throat while playing with these are called ‘sentinal nodes’. The enlarged small coins, puts 3 coins in his mouth. When asked bronchomediastinal lymph nodes may exert pressure by his mother, he takes out two of them, and is not on the left recurrent laryngeal nerve in the thorax able to take out one. causing alteration of voice. The cancer of lung is Where is the third coin likely to pass? mostly due to smoking. What can be the dangers to the boy? Ans: Since the boy was having sore throat, it is likely the coin has been inhaled into his respiratory FURTHER READING passages. The coin would pass down the larynx, Chandrupatla M, Krishnaiah. The study of bronchial tree. trachea, right principal bronchus, as it is in line with International Journal of Pharma and Biological Sciences trachea. The coin further descends into lower lobe 2011;2:166–72. bronchus, and into its posterior basal segment. That Hush A. Asthma research: The real action is in children. segment of the lung would get blocked, causing Paediatr Respair Rev 2005;6:101–10. respiratory symptoms. A review of how early problems with lung growth and development impact on later lung disease. If the coin goes into oropharynx and oesophagus, Morrisery EE, Hogan BL. Preparing for the first breath: it will comfortably travel down whole of digestive Genetic and cellular mechanisms in lung development. Dev tract and would come out in the faecal matter next Cell 2010;18:8–23. day. This paper presents an overview of the molecular mechanisms of Case 2 lung development. A 45-year-old man complained of severe cough, loss Ornitz DM, Yoin. Signalling networks regulating of weight, alteration of his voice. He has been development of the lower respiratory tract. Cold Spring Harb smoking for last 25 years. Radiograph of the chest ZPerspect Biol 2012;1;4. followed by biopsy revealed bronchogenic car- This paper presents a review of the signaling factors in lung cinoma in the left upper lobe of the lung. development. Where did the cancer cells metastasise? Shabana S, Mrudula C. Anatomical variations of pulmonary What caused alteration of his voice? veins at the hilum of lung. Int J Applied Research 2017;7:50– 51. 1–4 From Medical Council of India, Competency based Undergraduate Curriculum for the Indian Medical Graduate, 2018;1:44–80. Thorax 2 1. Describe the gross anatomy of the lungs. Define a b. Carina of trachea bronchopulmonary segment. Enumerate the Section segments of the lungs. What is the clinical c. Postural drainage importance of these segments? d. Effects of parasympathetic nerves on the lung 2. Write short notes on: e. Various subdivisions of a segmental bronchus a. Comparison of the roots of right and left lungs f. Intrapulmonary bronchus