Circulatory System Structure and Blood Flow Dynamics (3B) Practice Test

In a vascular imaging study, two arterioles of equal length were compared: Arteriole A had radius $r$, and Arteriole B had radius $2r$. Blood viscosity and pressure gradient were similar, and flow was laminar. The central principle is that resistance varies inversely with $r^4$, making small radius changes powerful for perfusion homeostasis. Which outcome would be expected when comparing the two vessels?

In an intensive care study, norepinephrine infusion increased systemic arteriolar tone. MAP rose from 60 to 80 mmHg, while cardiac output measured by thermodilution decreased from 4.5 to 3.8 L/min. The central principle is that increasing total peripheral resistance can raise MAP even if CO falls, supporting perfusion pressure homeostasis in shock. Based on the data, which conclusion is most consistent?