This article states that rapid redistribution of blood flow occurs to secure oxygen and energy for the active muscles, heart, and lungs, while blood is reduced in the splanchnic area. It also says that reduction of splanchnic circulation during exercise induces a physiological state of hypoperfusion in the gastrointestinal system.

This review explains that splanchnic blood flow is a major determinant of portal inflow and that changes in the splanchnic vascular bed strongly affect systemic circulation. Although it focuses on vasodilation in cirrhosis rather than stress responses, it confirms the importance of splanchnic vascular tone in blood redistribution.

During stress, splanchnic blood flow is redistributed to other organs to maintain vital organ perfusion. The gut is particularly vulnerable to ischemia during low-flow states such as shock because of intense vasoconstriction of the splanchnic circulation. In states of hypovolemia and shock, sympathetic activation results in vasoconstriction and diversion of blood away from the splanchnic organs to preserve blood flow to the heart and brain.

The splanchnic circulation is the most compliant vascular bed in humans and it receives a large fraction (~25%) of the total cardiac output at rest. Constriction of the splanchnic circulation either by the baroreflexes or pressor drugs, and the subsequent decrease in splanchnic vascular capacity, has the potential to buffer the fall in cardiac filling pressure that attends orthostasis. These data indicate that octreotide improves orthostatic tolerance by decreasing total vascular conductance and by increasing cardiac filling pressure via a reduction in unstressed vascular volume.

Upkeeping organs perfusion is one of the main goals of shock management, and to that end, volume resuscitation and vasopressors administration are key to maintaining adequate blood pressure. Firstly, the restoration of microcirculatory blood flow is not distributed evenly when vasopressors are used, especially in the digestive organs. In pigs who were exposed to fecal peritonitis-induced septic shock, norepinephrine and epinephrine failed to increase microcirculatory blood flow in most abdominal organs, despite increased perfusion pressure and systemic blood flow; these drugs appeared to divert blood flow away from the mesenteric circulation and decrease microcirculatory blood flow in the jejunal mucosa and pancreas.

During shock, sympathetic activation causes intense vasoconstriction of the splanchnic circulation and redistribution of blood flow to maintain perfusion of the heart and brain. The gut and liver therefore experience a marked reduction in perfusion during low-flow states, which may contribute to mucosal ischemia and barrier dysfunction.

Vasoconstriction of inactive tissues helps redistribute blood flow to active skeletal muscle to avoid outstripping cardiac output. During whole-body exercise or acute stress, increased muscle sympathetic nerve activity causes vasoconstriction in vascular beds such as the splanchnic region and kidneys, thereby preserving arterial pressure and directing blood flow to contracting skeletal muscle.

Harvard Health explains that the sympathetic nervous system triggers the fight-or-flight response and controls constriction or dilation of key blood vessels and small airways in the lungs. The article identifies this as part of the body’s stress response, which is relevant to acute redistribution of blood flow.

Changing from a supine to an upright posture or applying lower body negative pressure produces redistribution of venous volume with marked secondary changes in ventricular filling and stroke volume. Reflex-induced splanchnic vasoconstriction probably produces a passive decrease in venous volume in the splanchnic area, and radionuclide measurements suggest a large contribution from this region. Such splanchnic vasoconstriction and blood mobilization help maintain central blood volume and cardiac output, illustrating how the splanchnic bed acts as a reservoir that can be constricted during stress to support perfusion of vital organs.

Cleveland Clinic states that blood flow is redirected during the fight-or-flight response and that people may feel cool or clammy because circulation is shifted away from the skin and other less immediately necessary areas. This is consistent with sympathetic prioritization of organs and skeletal muscle during acute stress.

Splanchnic ischemia and reperfusion damage threaten the mucosal barrier function of the intestine leading to bacterial translocation, immune activation and, potentially, multiple organ failure. In stress states, vasoconstriction in the splanchnic region is part of the circulatory adaptation, redistributing blood flow from the gastrointestinal tract to more vital organs such as the heart and brain.

This page states that the splanchnic circulation normally receives over 25% of cardiac output and contains a similar percentage of total blood volume. That provides baseline context for why vasoconstriction in this bed can materially change perfusion distribution.

In acute sympathetic activation, norepinephrine acting on alpha-1 adrenergic receptors causes vasoconstriction in many splanchnic vessels, reducing gastrointestinal perfusion; cardiac output is redistributed toward skeletal muscle and, to support the response, the heart and lungs receive increased effective perfusion. This is standard physiology consistent with the fight-or-flight response.