Final answer:
When arteriovenous anastomoses are stimulated by sympathetic nerve fibers, capillary loops are bypassed to redirect blood flow to areas of greater need, such as active skeletal muscles.
Step-by-step explanation:
When the arteriovenous anastomoses are stimulated by sympathetic nerve fibers, the superficial capillary loops are bypassed. Arteriovenous anastomoses are vascular structures that allow blood to flow directly from arterioles to venules, and they are under the control of the sympathetic nervous system. During this process, the precapillary sphincters are closed, creating a direct path from arteries to veins, thus preventing blood from flowing through the capillary beds in that region.
This mechanism helps to regulate body temperature and redirects blood flow to areas where it is needed most, such as to active skeletal muscles during the fight-or-flight response.