Thymus, Trachea & Oesophagus

Thorax Unit Lecture 9 & 10

األعسم. جليل حيدر د

ThymusIt is a pink, flattened, bi-lobed structure lying between sternum and pericardium in anterior mediastinum. In newborn infants, it reaches its largest size relative to size of body & may extend up through superior mediastinum in front of great vessels into root of the neck. Blood Supply of thymus is from inferior thyroid and internal thoracic arteries.

TracheaTrachea is a mobile cartilaginous & membranous tube. It is 11 cm long and 2.5 cm in diameter. Tube is kept patent by presence of U-shaped bars (rings) of hyaline cartilage embedded in its wall. Posterior free ends of cartilage are connected by smooth muscle,trachealis muscle. It begins in neck as a continuation of larynx at lower border of cricoid cartilage at level of 6th cervical vertebra. In thorax, trachea ends below at carina by dividing into right & left principal (main) bronchi at level of sternal angle.

Blood Supply of TracheaUpper 2/3 by inferior thyroid arteries &Lower 1/3 is supplied by bronchial arteries.

Lymph Drainage of Trachea: into pretracheal & paratracheal lymph nodes & deep cervical nodes.

Nerve Supply of Trachea: is from vagi & recurrent laryngeal nerves. Sympathetic nerves supply trachealis muscle.

TracheaRelations of Trachea:Anteriorly: sternum, thymus, left brachiocephalic vein, origins of brachiocephalic & left common carotid arteries, & arch of aortaPosteriorly: esophagus & left recurrent laryngeal nerve.Right side: azygos vein, right vagus nerve, and pleuraLeft side: aortic arch, left common carotid & left subclavian arteries, left vagus & left phrenic nerves & pleura.

BronchiTrachea bifurcates behind arch of aorta into right & left principal (primary or main) bronchi. Right principal (main) bronchus is wider, shorter, and more vertical than left. Before entering hilum of right lung, it gives off superior lobar bronchus. On entering hilum, it divides into middle and inferior lobar bronchus. Left principal (main) bronchus is narrower, longer, and more horizontal than right. It passes to left below arch of aorta & in front of esophagus.On entering hilum of left lung, principal bronchus divides into a superior & an inferior lobar bronchus

EsophagusIt is a tubular structure about 10 in. (25 cm) long that is continuous above with pharynx & passes through diaphragm at level of 10th thoracic vertebra to join stomach.In neck, it lies in front of vertebral columnIn thorax, it passes downward & to left through superior & then posterior mediastinum. At level of sternal angle, aortic arch pushes esophagus over to midline.In abdomen, It descends for about 0.5 inch (1.3 cm) & then enters the stomach.

Relations of thoracic part of esophagusAnteriorly: Trachea and left recurrent laryngeal nerve; left principal bronchus, which constricts it; and pericardium, which separates esophagus from left atrium.Posteriorly: Bodies of thoracic vertebrae; thoracic duct; azygos veins; right posterior intercostal arteries; and, at its lower end, descending thoracic aorta.Right side: Mediastinal pleura and terminal part of azygos veinLeft side: Left subclavian artery, aortic arch, thoracic duct, and mediastinal pleura.Inferiorly to level of roots of lungs, vagus nerves leave pulmonary plexus and join with sympathetic nerves to form esophageal plexus. Left vagus lies anterior to esophagus and right vagus lies posterior.

EsophagusBlood Supply of EsophagusUpper 1/3: by inferior thyroid arteryMiddle 1/3: by branches from descending thoracic aortaLower 1/3: by branches from left gastric artery. Veins of upper 1/3 drain into inferior thyroid veins, from middle 1/3 into azygos veins, and from lower 1/3 into left gastric vein.

Lymph Drainage of EsophagusUpper 1/3 of esophagus drain into deep cervical nodes, Middle 1/3 into mediastinal nodes, Lower 1/3 into nodes along left gastric blood vessels &celiac nodes.

Nerve Supply of EsophagusEsophagus is supplied by parasympathetic & sympathetic efferent and afferent fibers via vagi & sympathetic trunks. In lower part of its thoracic course, esophagus is surrounded by esophageal nerve plexus.

Internal Thoracic ArteryIt supplies anterior wall of body from clavicle to umbilicus. It is a branch of first part of subclavian artery. It descends vertically on pleura behind costal cartilages, one fingerbreadth lateral to sternum, and ends in 6th intercostal space by dividing intosuperior epigastric arterymusculophrenic arteries.

Internal Thoracic ArteryBranches1. Two anterior intercostal arteries for upper six intercostal spaces2. Pericardiophrenic artery accompanies phrenic nerve & supplies Pericardium.3. Mediastinal arteries supply contents of anterior mediastinum (Thymus)4. Superior epigastric artery, entersrectus sheath of anterior abdominal wall & supplies rectus muscle as far as umbilicus5. Musculophrenic artery, runs around costal margin of diaphragm & supplies lower intercostal spaces & diaphragm

Internal Thoracic Vein: accompanies internal thoracic artery and drains into brachiocephalic vein on each side.