The Aorta

Ascending Aorta

The ascending aorta arises from the aortic orifice of the left ventricle and ascends to become the aortic arch.

It is approximately 5 cm (2 inches) long and enclosed within the pericardial sac, ascending with the pulmonary trunk.

Branches

At its root, the ascending aorta contains two aortic sinuses – small dilatations located just above the cusps of the aortic valve.

• Right aortic sinus gives rise to the right coronary artery.

• Left aortic sinus gives rise to the left coronary artery.

These vessels supply the myocardium of the heart and are the only branches of the ascending aorta.

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Aortic Arch

The aortic arch is a continuation of the ascending aorta, beginning at the level of the second sternocostal.

It arches superiorly, posteriorly, and to the left, before descending to end at the level of the T4 vertebra, where it continues as the thoracic aorta.

The aortic arch is connected to the pulmonary trunk by the ligamentum arteriosum, a fibrous remnant of the foetal ductus arteriosus.

Branches

From proximal to distal, three major branches arise from the aortic arch:

• Brachiocephalic trunk – the first and largest branch, which divides into the right common carotid and right subclavian arteries supplying the right side of the head, neck, and upper limb.
• Left common carotid artery – supplies the left side of the head and neck.
• Left subclavian artery – supplies the left upper limb.

By TeachMeSeries Ltd (2025)

Fig 2
Schematic of the aortic arch and major branches.

Thoracic Aorta

The thoracic aorta begins at the lower border of the T4 vertebra and descends through the posterior mediastinum to the aortic hiatus of the diaphragm at the level of T12, where it becomes the abdominal aorta.

Initially positioned to the left of the vertebral column, it gradually moves towards the midline as it descends.

Branches

In descending order:

• Bronchial arteries: Paired visceral branches arising laterally to supply bronchial and peribronchial tissue and visceral pleura. However, most commonly, only the paired left bronchial artery arises directly from the aorta whilst the right branches off usually from the third posterior intercostal artery.
• Mediastinal arteries: Small arteries that supply the lymph glands and loose areolar tissue in the posterior mediastinum.
• Oesophageal arteries: Unpaired visceral branches arising anteriorly to supply the oesophagus.
• Pericardial arteries: Small unpaired arteries that arise anteriorly to supply the dorsal portion of the pericardium.
• Superior phrenic arteries: Paired parietal branches that supply the superior portion of the diaphragm.
• Intercostal and subcostal arteries: Small paired arteries that branch off throughout the length of the posterior thoracic aorta. The 9 pairs of intercostal arteries supply the intercostal spaces, with the exception of the first and second (they are supplied by a branch from the subclavian artery). The subcostal arteries supply the flat abdominal wall muscles.

By TeachMeSeries Ltd (2025)

Fig 3
Lateral view of the thoracic aorta, with the intercostal branches shown.

Abdominal Aorta

The abdominal aorta begins at the level of T12, immediately below the aortic hiatus of the diaphragm, and descends anterior to the vertebral column.

It terminates at the level of L4, dividing into the right and left common iliac arteries. Its average length is approximately 13 cm.

Branches

In descending order:

• Inferior phrenic arteries: Paired parietal arteries arising posteriorly at the level of T12. They supply the diaphragm.
• Coeliac artery: A large, unpaired visceral artery arising anteriorly at the level of T12. It is also known as the celiac trunk and supplies the liver, stomach, abdominal oesophagus, spleen, the superior duodenum and the superior pancreas.
• Superior mesenteric artery: A large, unpaired visceral artery arising anteriorly, just below the celiac artery. It supplies the distal duodenum, jejuno-ileum, ascending colon and part of the transverse colon. It arises at the lower level of L1.
• Middle suprarenal arteries: Small paired visceral arteries that arise either side posteriorly at the level of L1 to supply the adrenal glands.
• Renal arteries: Paired visceral arteries that arise laterally at the level between L1 and L2. They supply the kidneys.
• Gonadal arteries: Paired visceral arteries that arise laterally at the level of L2. Note that the male gonadal artery is referred to as the testicular artery and in females, the ovarian artery.
• Inferior mesenteric artery: A large, unpaired visceral artery that arises anteriorly at the level of L3. It supplies the large intestine from the splenic flexure to the upper part of the rectum.
• Median sacral artery: An unpaired parietal artery that arises posteriorly at the level of L4 to supply the coccyx, lumbar vertebrae and the sacrum.
• Lumbar arteries: There are four pairs of parietal lumbar arteries that arise posterolaterally between the levels of L1 and L4 to supply the abdominal wall and spinal cord.

By TeachMeSeries Ltd (2025)

Fig 4
The abdominal aorta and its major branches.

By OpenStax College [CC BY 3.0], via Wikimedia Commons

Fig 5
Schematic of the branches of the thoracic and abdominal aorta.

Clinical Relevance

Aortic Aneurysm

Aortic aneurysm describes a dilation of the artery to more than 1.5 times its original size. The abdominal component of the aorta is the most common site for aneurysmal changes.

Patients suffering with an abdominal aortic aneurysm may experience abdominal pulsations, abdominal pain and back pain. The aneurysm may also compress nerve roots causing pain/numbness in the lower limbs. A patient with an aortic arch aneurysm may have a hoarse voice due to the dilation stretching the left recurrent laryngeal nerve. Patients may also not have any symptoms at all.

Small aortic aneurysms do not usually pose a serious immediate threat. Diagnosis is made from an ultrasound and the weakened vessel wall can be surgically replaced with a piece of synthetic tubing. If left untreated, a large aneurysm can rupture. This is a medical emergency and often fatal.

By TeachMeSeries Ltd (2025)

Fig 6
Aortic aneurysm, a dilation of the vessel more than 1.5 times the original diameter.