During the first 5 minutes of exercise, which vascular resistance is most likely to increase significantly?

During the first 5 minutes of exercise, the vascular resistance in the splanchnic circulation is most likely to increase significantly. This phenomenon occurs as the body prioritizes blood flow to skeletal muscle and other tissues that are actively engaged in exercise, while reducing blood flow to less critical areas such as the gastrointestinal tract.

During exercise, there is increased sympathetic nervous system activity that causes vasoconstriction in various vascular beds, including the splanchnic circulation. This redirection of blood flow enhances delivery to regions that require oxygen and nutrients more immediately, like the muscles, while diverting blood away from the digestive organs, which are not as active during physical exertion.

In contrast, vascular resistance in the exercising muscle typically decreases due to local factors that promote vasodilation, such as metabolic byproducts and an increase in demand for oxygen. The coronary circulation accommodates increased blood flow to meet the heightened demands of the heart itself. The pulmonary circulation, while also affected by exercise, does not experience a significant increase in resistance in the same way as splanchnic circulation.

Thus, the increase in vascular resistance during the initial phase of exercise is primarily associated with the need to redirect blood flow away from the splanchnic system toward the more actively