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Figure 18.1. Pharynx showing cricothyroid membrane for minitracheostomy.

SURGICAL ANATOMY Tracheobronchial tree

The larynx is the gateway to the tracheobronchial tree and is guarded by the false and true vocal cords. The true vocal cords are important in phonation and also participate in the protection of the airway from fluid and food during deglutition. They are largely controlled by the recurrent laryngeal nerves which both originate in the chest from the vagus nerve and thus are liable to be compromised by any intra-thoracic disease.

The main body of the larynx is protected by the hyoid bone and the trachea is suspended from the cricoid bone. There is a membrane in between and this is a useful landmark for emergency cricothyroidotomy or insertion of a minitracheostomy (Fig. 18.1). The trachea and main bronchi are held open by cartilaginous rings. In the former, the rings are incomplete with a posterior membrane and immediately behind the membrane lies the cervical oesophagus. The recurrent laryngeal nerves ascend in this groove. The tracheo-bronchial tree is lined with ciliated epithelium containing glands secreting mucus and mucus is passed upwards after trapping inhaled particles of foreign material. When the

Figure 18.1. Pharynx showing cricothyroid membrane for minitracheostomy.

lining is damaged, such as by chronic smoking, the mucus becomes tenacious, the cilia are deficient and the patient has to cough to clear mucus adequately. This is particularly noticeable first thing in the morning and an early morning cough is the hallmark of chronic smokers.

The lungs are divided into lobes, three on the right and two on the left, and each lobe has two or more segments each served by an independent bronchus. A knowledge of the bronchial anatomy is important for bronchoscopy so that the correct segment can be readily identified (Fig. 18.2). The lungs receive their blood supply from bronchial arteries and are not dependent on the pulmonary circulation. The lymphatic drainage of the segments is first to segmental then hilar lymph nodes and ultimately up to the scalene node on either side. There is, however, a significant cross over of lymphatic drainage from one side to the other, particularly from the left lower lobe to the subcarinal and right-sided glands (Fig. 18.3).

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