Why is the ICA considered low resistance?

• A. It has many branches
• B. It is smaller than the ECA
• C. It has high pulsatility
• D. Because it feeds the brain, and the brain requires constant perfusion

Answer: (D)

The main idea here is that the brain needs a steady, reliable blood supply, so the cerebral circulation is a low-resistance pathway. The internal carotid artery acts as a large-diameter conduit feeding the brain’s extensive vascular bed, and the brain’s autoregulatory mechanisms keep cerebral blood flow constant over a range of blood pressures. This combination means the flow through the ICA encounters relatively little resistance to deliver continuous perfusion to neural tissue. The other choices don’t capture this functional requirement: while cerebral vessels do form parallel pathways, the key point is the brain’s demand for constant perfusion; the ICA’s role as the high-flow, low-resistance route to meet that demand explains why it’s considered low resistance.