1 THE AORTA AND IT S MAJOR BRANCHES The aorta commences at the aortic valve, above the vestible of the left ventricle and terminates at the level of the fourth lumbar vertebra (L4), where it bifurcates to form the right and left common iliac arteries. It is an elastic artery and it is divisible into four parts, viz: 1. The Ascending thoracic aorta. 2. The Arch of the aorta. 3. The Descending thoracic aorta and 4. The Abdominal aorta. Figure 1.
2 ASCENDING THORACIC AORTA: This is located in the middle mediastinum within the pericardial cavity. It commences at the aortic valve and terminates at the manubrosternal junction. It is about 5cm long and has the following branches: The right and left coronary arteries, which supply the heart and the visceral pericardium are the only branches of the ascending aorta. THE ARCH OF THE AORTA: This is located in the superior mediastinum. It is the continuation of the ascending aorta at the manubrosternal junction. From this junction it courses superoposteriorly and to the left to end at the manubrosternal junction on the left aspect of the midline. It is connected at its concavity to the root of the left pulmonary artery by the ligamentum arteriosum. Its branches are: 1. The Brachiocephalic trunk. This gives rise to: a. Right Common Carotid artery. b. Right Subclavian artery. 2. Left Common Carotid artery. 3. Left Subclavian artery. Each common carotid artery bifurcates at the level of C4 to give rise to an internal and an external carotid artery. The internal carotid continues into the cranial cavity to supply cranial contents while the external carotid supplies the head and neck region. The branches of each internal carotid are: 1. Superior and inferior hypophyseal arteries 2. Meningeal arteries. 3. Ophthalmic artery. 4. Posterior communicating artery 5. Anterior choroidal artery 6. Anterior cerebral artery. ** 7. Middle cerebral artery. ** The branches of each external carotid artery are: 1. Superior thyroid artery. 2. Ascending pharyngeal artery. 3. Lingual artery. 4. Facial artery. 5. Occipital artery. 6. Posterior auricular artery. 7. Maxillary artery. ** 8. Superficial temporal artery. **
3 THE SUBCLAVIAN ARTERY (Figure 4) Each subclavian artery is subdivided into three parts by the scalenus anterior muscle. The first part, which lies medial to the scalenus anterior, has the following branches: a. The vertebral artery. b. The thyrocervical artery which gives rise to: i. Inferior thyroid art. ii. Superficial (Transverse) cervical art. iii. Suprascapular art. c. The internal thoracic (Mammary) art. The second part, which lies posterior/deep to the anterior scalene muscle, has the following branch: The costocervical art. This gives rise to: i. Superior (Highest) intercostal art. ii. Deep cervical art. The third part, which lies lateral to the anterior scalene muscle, has the following branch: a. The dorsal scapular art. Each Subclavian artery continues as the axillary artery at the outer margin (Lateral margin) of the first rib.the axillary artery is the main arterial supply to the upper limb. THE DESCENDING THORACIC AORTA This artery is the continuation of the arch of the aorta at the manubrosternal junction (T4/T5). It passes through the posterior mediastinum and terminates posterior to the median arcuate ligament of the diaphragm at the level of the 12 th thoracic vertebra (T12). At this point it continues as the Abdominal aorta. The branches of the descending thoracic aorta include: 1. 9 pairs of Posterior intercostal arteries. 2. A pair of subcostal arteries. 3. 2 left bronchial art. 4. 2 oesophageal art. 5. Pericardial branches (Unknown number). 6. Mediasternal branches (Unknown number). 7. A pair of Superior Phrenic art. (Right & Left).
Figure 2. 4
5 THE ABDOMINAL AORTA (Figure 3) This is the continuation of the descending thoracic aorta at the level of T12. It is located on the posterior abdominal wall and terminates at the level of L4. Here it bifurcates to give rise to the right and left Common iliac arteries. Its branches include: 1. The unpaired median branches: a. Coeliac trunk. ( Foregut) b. Superior mesenteric art. (Midgut) c. Inferior mesenteric art. (Hindgut) d. Median sacral art. 2. The paired visceral branches: a. Renal art. b. Middle suprarenal art. c. Testicular/Ovarian art. 3. The paired parietal branches: a. Inferior phrenic art. b. 4 pairs of Lumbar art. Each of the Common iliac arteries will bifurcate at the level of the sacroiliac joint to give rise to Internal and External iliac arteries. The internal iliac artery will supply the pelvic, perineal and gluteal regions. The external iliac continues as the Femoral artery beyond the inguinal ligament to supply the entire lower limb.
Figure 3. 6
Figure 4. 7