The ascending aorta arises from the aortic vestibule behind the
infundibulum of the right ventricle and the pulmonary trunk. It is continuous
with the aortic arch. The arch lies posterior to the lower half of
the manubrium and arches from front to back over the left main
bronchus. The descending thoracic aorta is continuous with the arch
and begins at the lower border of the body of T4. It initially lies slightly
to the left of the midline and then passes medially to gain access to the
abdomen by passing beneath the median arcuate ligament of the
diaphragm at the level of T12. From here it continues as the abdominal
aorta.
The branches of the ascending aorta are the:
• Right and left coronary arteries.
The branches of the aortic arch are the:
• Brachiocephalic artery: arises from the arch behind the manubrium
and courses upwards to bifurcate into right subclavian and right common
carotid branches posterior to the right sternoclavicular joint.
• Left common carotid artery:
• Left subclavian artery.
• Thyroidea ima artery.
The branches of the descending thoracic aorta include the:
• Oesophageal, bronchial, mediastinal, posterior intercostal and subcostal
arteries.
The subclavian arteries (see Fig. 60.1)
The subclavian arteries become the axillary arteries at the outer border
of the 1st rib. Each artery is divided into three parts by scalenus
anterior:
• 1st part: the part of the artery that lies medial to the medial border of
scalenus anterior. It gives rise to three branches, the: vertebral artery
thyrocervical trunk and internal thoracic (mammary) artery.
The latter artery courses on the posterior surface of the anterior chest
wall one fingerbreadth from the lateral border of the sternum. Along
its course it gives off anterior intercostal, thymic and perforating
branches. The ‘perforators’ pass through the anterior chest wall to
supply the breast. The internal thoracic artery divides behind the 6th
costal cartilage into superior epigastric and musculophrenic branches.
The thyrocervical trunk terminates as the inferior thyroid artery.
• 2nd part: the part of the artery that lies behind scalenus anterior. It
gives rise to the costocervical trunk (see Fig. 60.1).
• 3rd part: the part of the artery that lies lateral to the lateral border of
scalenus anterior. This part gives rise to the dorsal scapular artery.
The great veins (Fig. 4.2)
The brachiocephalic veins are formed by the confluence of the subclavian
and internal jugular veins behind the sternoclavicular joints. The
left brachiocephalic vein traverses diagonally behind the manubrium to
join the right brachiocephalic vein behind the 1st costal cartilage thus
forming the superior vena cava. The superior vena cava receives only
one tributaryathe azygos vein.
The azygos system of veins (Fig. 4.2)
• The azygos vein: commences as the union of the right subcostal vein
and one or more veins from the abdomen. It passes through the aortic
opening in the diaphragm, ascends on the posterior chest wall to the
level of T4 and then arches over the right lung root to enter the superior
vena cava. It receives tributaries from the: lower eight posterior intercostal
veins, right superior intercostal vein and hemiazygos veins.
• The hemiazygos vein: arises on the left side in the same manner as the
azygos vein. It passes through the aortic opening in the diaphragm and
up to the level of T9 from where it passes diagonally behind the aorta
and thoracic duct to drain into the azygos vein at the level of T8. It
receives venous blood from the lower four left posterior intercostal
veins.
• The accessory hemiazygos vein: drains blood from the middle posterior
intercostal veins (as well as some bronchial and mid-oesophageal
veins). The accessory hemiazygos crosses to the right to drain into the
azygos vein at the level of T7.
• The upper four left intercostal veins drain into the left brachiocephalic
vein via the left superior intercostal vein.
The
The respiratory tract is most often discussed in terms of upper and
lower parts. The upper respiratory tract relates to the nasopharynx and
larynx whereas the lower relates to the trachea, bronchi and lungs
Structure:
the trachea is a rigid fibroelastic structure. Incomplete
rings of hyaline cartilage continuously maintain the patency of
the lumen. The trachea is lined internally with ciliated columnar
epithelium.
•
Relations: behind the trachea lies the oesophagus. The 2nd, 3rd and
4th tracheal rings are crossed anteriorly by the thyroid isthmus (Figs 5.3
and 64.1).
•
Blood supply: the trachea receives its blood supply from branches of
the inferior thyroid and bronchial arteries.
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