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Definition: It is a fibromuscular tube 10 cm long containing incomplete cartilaginous rings. Beginning: At the lower border of the cricoid cartilage (at the level of C 6). Course: - It begins in the midline and terminates slightly to the right of the midline. - It lies in the superior mediastinum. Termination: - At the level of T 4 (sternal angle). - Anterior: Innominate artery, left innominate vein and thymus gland. - Posterior: Oesophagus and left recurrent laryngeal nerve. - Right: Right vagus, arch of azygos, right lung and pleura. - Left: Arch of the aorta,left common carotid and subclavian arteries, left vagus and phrenic nerves. Blood supply: a. Inferior thyroid arteries. b. Bronchial arteries from the descending thoracic aorta (left side). c. Right superior intercostal artery (right side). - It is drained by the inferior thyroid veins. Nerve supply: - Sympathetic ---- Sympathetic trunk. - Parasympathetic ---Vagi nerves. The trachea terminates at the level of T 4 by dividing into right and left main bronchi which are asymmetrical. - When a foreign body enters the trachea it passes through the right main bronchus. Right Main Bronchus Left Main Bronchus - Shorter (1 inch). - Longer (2inches). - Wider. - Narrower. - More in line with the trachea. - More horizontal. - Divides before its entry into the lung. - Divides inside the lungs. - The trachea divides into right and left main bronchi. With more division of the main bronchi they give rise to lobar then segmental bronchi. Each segmental bronchus is distributed to a localized part of lung tissue forming what is called the broncho-pulmonary segments. The right bronchus divides into: 1superior lobar bronchus and 2middle and inferior lobar bronchus. The left bronchus divides into superior and inferior lobar bronchi. Each lobar bronchus is divided into segmental bronchi. Right bronchus Superior lobar bronchus 1. Apical 3. Posterior 2. Anterior Middle lobar bronchus 4. Medial Inferior lobar bronchus 6. Apical basal 7. Medial basal 8. Lateral basal 9. Anterior basal 10. Posterior basal 5. Lateral Left bronchus 1. Apicoposterior 3. Sup. lingular 2. Anterior 4. Inf. lingular ---------------------------------------------------- 5. Apical basal 6. Lateral basal 7. Anteromedial basal 8. Posterior basal Origin: *Endoderm of foregut endothelium& glands. *Splanchnic mesoderm Ms, CT, tracheal rings. Development: * Ventral border of oesophagus laryngotracheal diverticulum ( opened cranially& blind caudally) Elongates, separates from the oesophagus trachea. Development: *The blind caudal end of the trachea dilates gives lung bud divides into right and left buds. *Right lung bud three branches: 1-Upper lat. branch upper lobe bronchus . 2-Stem lower lobe bronchus. 3-Lower lat. Branchmiddle lobe bronchus. 1-Upper lobe bronchus three branches (3ry): a. Apical b. Anterior c. Posterior 2-Lower lobe bronchus five branches (3ry): a. Apical basal b. Anterior basal c.Posterior basal d. Medial basal e. Lateral basal 3- Middle lobe bronchus two branches (3ry): a.Medial b. Lateral *Left lung bud (1ry ) two branches: 1-One lat. Branch(2ry) upper lobe bronchus. 2-Stem lower lobe bronchus. 1-Upper lobe bronchus two branches (3ry): A-Upper: a. Apicoposterior b. Anterior B- Lower ( lingular): a. Superior b. Inferior 2-Lower lobe bronchus four branches (3ry): a. Apical basal b. Anteromedial basal c.Posterior basal d. Lateral basal • • • Each tertiary bronchiole divides repeatedly 18 generations. The final generation dilates alveoli. After birth extra 6 generations until the age of 8 years 18+ 6= 24 generations. 1- Tracheo-oesophageal fistula: No separation between the trachea and oesophagus *milk pass to the lungpneumonia. *air pass to stomach dilatation resp. impairment. 2- Variation in the number of lobes of the lung. 3- Congenital cysts of a lung: Due to dilatation of terminal bronchioles. 4- Congenital atelectasis of a lung or lobe: due to obstruction of 1ry or 2ry bronchioles. 5- Respiratory distress syndrom: Due to deficiency of surfactants secreted from type II pneumocytesno dilatation of alveoli death. Prof.: Dr. Wafaa Abdel-Rahman