Final answer:
Blood in the right subclavian artery comes from the brachiocephalic artery, which branches from the aortic arch and supplies blood to the upper body and brain.
Step-by-step explanation:
The blood in the right subclavian artery originates from the brachiocephalic artery, which is a single vessel located on the right side of the body. The brachiocephalic artery is the first major branch from the aortic arch, and it subsequently divides into the right subclavian artery and the right common carotid artery. The right subclavian artery then supplies blood to various parts of the body including the arms, chest, shoulders, back, and components of the central nervous system. Notably, the left subclavian artery, in contrast to the right, arises directly from the aortic arch.