Which artery is not a direct branch of the celiac axis?

The superior mesenteric artery is not a direct branch of the celiac axis; instead, it arises independently from the aorta, typically just below the origin of the celiac trunk. The celiac axis, also known as the celiac trunk, primarily gives rise to the left gastric, common hepatic, and splenic arteries. These arteries supply blood to various structures in the upper abdominal organs, such as the liver, stomach, and spleen. Understanding the branching of these major arteries is crucial in the context of abdominal ultrasound as it helps in identifying vascular anatomy and potential pathologies during imaging. Thus, recognizing that the superior mesenteric artery stems directly from the aorta reinforces the knowledge of vascular anatomy, critical for any ultrasound examination focused on the abdomen.