Tbtttttt. 12345. 3.pptx

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1. TRACHEOBRONCHIAL TREE BY- DR. NEHAL NAUTIYAL

2. TRACHEA (generation 0): It is a midline structure that extends from lower end of cricoid cartilage at the level of C6 vertebra to its termination at bronchial bifurcation (T4) It comprises of 16-20 C shaped cartilage rings which are joined vertically by fibroelastic tissue and closed posteriorly by non striated trachealis muscle U shaped cartilage helps in keeping the lumen patent. Adult- length 10-12 cm and diameter 15-20 mm Children- trachea is smaller, deeply placed and more mobile

3. ANATOMY: Trachea divides into right and left primary main bronchi. Each further divides into lobar bronchi which in turn give rise to segmental bronchi which supply air to bronchopulmonary segments Segmental bronchi divide dichotomously, eventually giving rise to terminal bronchioles which further terminates into respiratory bronchioles. Originating from each respiratory bronchioles are 2-11 alveolar ducts leading to alveolar sacs which are extended as a group of alveoli. The airways branch over an average of 23 generations of dichotomous branching, ending eventually in a blind sac.

4. Airway becomes progressively narrower, shorter and more numerous and cross sectional area enlarges. Areas of tracheobronchial tree farthest from the trachea are collectively called the ‘distal respiratory tree’. The first 14 generations are purely conducting airways. Transitional airways (generation 15) lead into the acinar airways with alveoli that branch over 8 generations.

5. RELATIONS OF TRACHEA- A nteriorly:   sternum ,  strap muscles ,  thyroid isthmus ,  ascending aorta , brachiocephalic artery,  right common carotid artery ,  superior vena cava,  inferior thyroid veins,  left brachiocephalic vein   Posteriorly:   esophagus   Laterally:  lateral walls of the  thyroid gland ,  left common carotid artery , arch of the  azygos vein , right and left  recurrent laryngeal nerves ,  right and left vagus nerves

6. RIGHT MAIN BRONCHUS- The right main bronchus is 2 cm long and has an internal diameter of 10—16 mm. It is wider, shorter and more vertical than the diameter of left main bronchus. Right main bronchus divides into right upper lobe bronchus and bronchus intermedius. The bronchus intermedius of right bronchial tree is quite short, extending for 1—2.5 cms until its anterior wall extends and becomes the middle lobe bronchus . Its posterior wall extends and becomes the right lower lobe bronchus.

7. The right upper lobe bronchus divides into- APICAL bronchus ANTERIOR bronchus POSTERIOR bronchus The middle lobe bronchus further divides into- MEDIAL segmental bronchus LATERAL segmental bronchus The right lower lobe bronchus divides into- SUPERIOR segmental bronchus MEDIAL BASAL segmental bronchus

8. LEFT MAIN BRONCHUS: The left main bronchus is usually 4-5 cms long. Its lumen is narrower and relatively horizontal. It divides into upper and lower lobe bronchus

9. The left upper lobe bronchus divides into- UPPER DIVISION- Apical Posterior Anterior LINGULAR BRONCHUS- Superior division Inferior division The left lower lobe bronchus divides into- Apical Anterior basal Posterior basal Lateral basal

10. SECONDARY CARINAS- Right carina/RC 1- between right upper lobe bronchus and bronchus intermedius RC 2- between right middle lobe and right lower lobe bronchus Left carina/LC 1- between upper and lingular division of left upper lobe. LC 2- between left upper and lower lobe bronchus

11. BRONCHIOLES (12-14 generations): The internal diameter is ~1 mm. Patency : Cartilage disappears from the airway wall below this level . The air passages are directly embedded in the lung parenchyma, the elastic recoil of which holds the air passages open . The total cross-sectional area increases which makes the flow resistance of these smaller air passages (less than 2 mm diameter) negligible under normal conditions.

12. The resistance of the bronchioles can increase to very high values when their strong helical muscular bands are contracted. The conducting airways derive their nutrition from the bronchial circulation and are influenced by systemic arterial blood gas levels. The acinar airways rely upon the pulmonary circulation for their nutrition.

13. Transition to Respiratory Bronchioles (Generations 15 to 18)- The function of the air passages is solely conduction and humidification. In the four generations of respiratory bronchioles there is a gradual increase in the number of alveoli in their walls. Like the earlier bronchioles, the respiratory bronchioles are embedded in lung parenchyma. There is no significant change in calibre of advancing generations of respiratory bronchioles (~0.4 mm diameter).

14. Alveolar Ducts (Generations 19 to 22) and Alveolar Sacs (Generation 23)- Arise from the terminal respiratory bronchiole, from which they differ by having no walls other than the mouths of mural alveoli (approximately 20 in number). The alveolar septa comprise a series of rings forming the walls of the alveolar ducts and containing smooth muscle. Approximately 35% of the alveolar gas resides in the alveolar ducts and the alveoli that arise directly from them. The last generation of the air passages differs from alveolar ducts solely because they are blind.

15. It is estimated that about 17 alveoli arise from each alveolar sac and account for about half of the total number of alveoli which occurs in larger airways. Millions of alveolar ducts branch off the respiratory bronchioles. Alveolar ducts are tiny airways only 0.3 mm in diameter, and their walls are composed entirely of alveoli. Each alveolar duct ends in a cluster of alveoli, which is frequently referred to as an alveolar sac. Each alveolar sac opens into about 16 or 17 alveoli, and about one-half the total number of alveoli are found in this region.

16. ALVEOLI- The mean total number of alveoli has been estimated as 400 million, but ranges from about 270 to 790 million, correlating with the height of the subject and total lung volume. The size is dependent on lung volume but due to gravity they are normally larger in the upper part of the lung, except at maximal inflation when the vertical gradient in size disappears. Alveolar walls are flat with sharp corners where the adjacent walls meet.

17. At functional residual capacity the mean diameter of a single alveolus is 0.2 mm and the total surface area of the alveoli is ~130 m2 . Intrinsic shape of alveoli (Al) is maintained from FRC to TLC.

18. Transition from conducting airway to the alveolus- As the conducting airway transitions to terminal and transitional bronchioles, the histological appearance of the conducting tubes change. Clara cells, non ciliated cuboidal epithelial cells that secrete important defense markers and serve as progenitor cells after injury, make up a large portion of the epithelial lining in the latter portions of the conducting airway

19. Secretory glands are absent from the epithelium of the bronchioles and terminal bronchioles, smooth muscle plays a more prominent role and cartilage is largely absent from the underlying tissue.

20. The epithelial layer transitions from pseudostratified layer with submucosal glands to a cuboidal and the to a squamous epithelium. The underlying mesynchyme tissue and capillary structure also changes with the airway transition. The cells of the respiratory mucosa change as they progress into the smaller airways. As the thickness of the airway walls decreases, bronchial glands become fewer in number. At the bronchiolar level, the number of ciliated cells decreases.

21. VASCULAR SUPPLY- Arterial supply- upper 2/3- inferior thyroid artery lower 1/3 – bronchial artery Venous supply- inferior thyroid vein Lymphatic drainage- drains into deep cervical LN, pretracheal LN and paratracheal LN Nerve supply- Vagus and RLN with sympathetic fibres from middle cervical ganglion

22. Bronchial arteries- Right bronchial artery- branch of 3 rd posterior intercostal artery Left bronchial artery- branch of thoracic aorta Bronchial veins- communicate with pulmonary vein Right side- drains in azygous vein Left side- drains in accessory hemiazygous vein

23. BRONCHOPULMONARY SEGMENTS: The bronchopulmonary segments are the anatomic structural and functional unit of lung parenchyma, each ventilated by a segmental / tertiary bronchus.

24. Characteristics- Pyramid in shape with apex directed towards lung root and subdivision of a lung lobe Surrounded by connective tissue that is continuous with visceral pleura Each segment can be delineated radiologically Diseased segment can be removed surgically without affecting the functioning of other segments. Each segment has its own separate artery, segmental bronchus, autonomic nerves and lymph vessels

25. BPS is drained by the intersegmental parts of the pulmonary veins , so during segmental resection surgeons work along pulmonary veins. Each segment has more than one vein and each vein drains more than one segment. Segmental vein runs in the connective tissue between adjacent BPS, thus it is not a bronchovascular segment.

26. RIGHT LUNG- Superior lobe- apical segment posterior segment anterior segment Middle lobe- lateral segment medial segment Inferior lobe- superior medial basal anterior basal lateral basal posterior basal

27. LEFT LUNG- Superior lobe- Apico -posterior Anterior segment Lingula of superior lobe- Inferior lingular Superior lingular Inferior lobe- Superior segment Anteromedial basal segment Posterior basal Lateral basal

28. APPLIED ASPECTS- Aspiration in supine position- superior segment of lower lobe of right lung Aspiration in standing position- posterior basal segment of lower lobe of right lung TB/ Septic Pneumonia- mostly affects posterior segment of right upper lobe Bronchiectasis- lower lobe is affected (L > R)

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