Final answer:
The aortic isthmus is located after the aortic arch and before the descending thoracic aorta, superior to the diaphragm.
Step-by-step explanation:
The aortic isthmus is a specific anatomical region of the aorta, the largest artery in the body. It is the portion of the descending aorta located immediately after the aortic arch. The isthmus sits superior to the aortic hiatus but inferior to where the aorta passes through the diaphragm. Specifically, it is the area before the aorta descends into the thoracic aorta and continues into the abdominal aorta. This section plays a crucial role in blood distribution as arteries branching from the aorta supply blood to virtually all body tissues. The abdominal aorta eventually bifurcates at the level of the fourth lumbar vertebra into the two common iliac arteries.