Ascending aorta
The first part of the vessel is the ascending part (pars ascendens aortae). It originates from the aortic orifice (ostium aortae) in the left ventricle. Spatially, this segment is localized behind the left half of the sternum, beginning at the level of the third intercostal space.
The vessel courses superiorly, slightly to the right and anteriorly, reaching the cartilage of the second rib on the right side. It is precisely at this point that the ascending aorta transitions smoothly into the aortic arch.
The very beginning of the ascending segment is noticeably expanded — this structure is termed the aortic bulb (bulbus aortae). Inside the bulb, the wall forms three characteristic pockets or protrusions, which are called the aortic sinuses (sinus aortae). Their arrangement strictly corresponds to the localization of the three cusps of the semilunar valve.
Depending on their position, three sinuses are distinguished:
- Right sinus (sinus aortae dexter) — gives rise to the right coronary artery.
- Left sinus (sinus aortae sinister) — from which the left coronary artery branches off.
- Posterior sinus (sinus aortae posterior) — is "blind" and has no arterial branches.
Aortic arch and its branches
The next segment is the aortic arch (arcus aortae). It arches from the cartilage of the second rib on the right and extends to the left surface of the bodies of thoracic vertebrae III–IV. The shape of the arch is convex superiorly and concave inferiorly. In the area where the arch ends and the descending part begins, there is a physiological narrowing of the vessel — the aortic isthmus (isthmus aortae).
From the superior (convex) aspect of the arch, three major arterial trunks arise from right to left:
- Brachiocephalic trunk (truncus brachiocephalicus). This is a large vessel about 4 centimeters long, running upward and to the right. Reaching the level of the right sternoclavicular joint, it divides into the right common carotid and right subclavian arteries. In rare cases, the thyroid ima artery (a. thyroidea ima) branches from it. There are anatomical variations: the trunk may be absent (in which case its branches arise directly from the arch), it may originate on the left side, or it may even be duplicated (right and left trunks).
- Left common carotid artery (a. carotis communis sinistra). It branches directly from the arch, which is why its length exceeds that of the corresponding artery on the right side.
- Left subclavian artery (a. subclavia sinistra). It runs upward and to the left, supplying blood to the neck region and the upper limb.
Descending aorta
The descending aorta (pars descendens aortae) serves as the direct continuation of the arch. It has the greatest length among all segments, starting at the level of the III–IV thoracic vertebrae and descending down to the fourth lumbar vertebra.
Topographically and functionally, this extensive segment is divided into two halves, with the diaphragm serving as the boundary between them:
- Thoracic aorta (pars thoracica aortae) — located in the thoracic cavity until it crosses the diaphragm.
- Abdominal aorta (pars abdominalis aortae) — begins after the vessel passes through the aortic hiatus of the diaphragm (at the level of the twelfth thoracic vertebra — Th12).
The descending aorta completes its course at the level of the IV lumbar vertebra. Here, its bifurcation (division) into the right and left common iliac arteries (aa. iliacae communes dextra et sinistra) takes place. The main trunk itself sharply diminishes in caliber and continues as a small median sacral artery (a. sacralis mediana), which descends along the anterior surface of the sacrum.
To remember the order of branches arising from the aortic arch (from right to left), use the mnemonic rule "BCC": Brachiocephalic trunk, Common carotid artery (left), Clavian/subclavian artery (left).
Class and exam questions
Which arteries originate from the aortic bulb?
From the aortic bulb (specifically, from the right and left aortic sinuses), the right and left coronary arteries arise, supplying the heart.
Where is the aortic isthmus located?
The aortic isthmus (isthmus aortae) is an anatomical narrowing located at the transition of the aortic arch into its descending part.
At what level does the aorta pass through the diaphragm?
The aorta pierces the diaphragm through a special aortic hiatus at the level of the twelfth thoracic vertebra (Th12).
Where and how does the descending aorta end?
At the level of the fourth lumbar vertebra, the aorta divides into two common iliac arteries, and its direct continuation becomes the slender median sacral artery.
What else to study on this topic
- Anatomy and blood supply of the coronary arteries
- Course and branches of the right and left common carotid arteries
- Topography of the subclavian arteries
- Structure and branches of the thoracic aorta
- Branches of the abdominal aorta
- Aortic bifurcation and common iliac arteries
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