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Autoregulation mechanism dominates over extrinsic mechanism (neuronal and hormonal influences). Because the gastrointestinal system does not have dominant autoregulation system, their vessels will constrict under SNS activity, and therefore, blood flow decreases to the gastrointestinal system during exercise. 1) Coronary circulation: auto-regulated by endogenous adenosine and nitric oxide. When the heart is under stress, more ATP will be used up, and adenosine will form as a byproduct. Adenosine dilates coronary vessels and provides sufficient blood flow to the heart to meet its energy requirements. 2) Cerebral circulation: brain maintains its circulation mainly by arterial carbon dioxide level (PaCO2). During exercise, cerebral circulation is unchanged because exercise will increase the level of venous blood carbon dioxide level, which subsequently undergoes pulmonary oxygenation before reaching to the brain. 3) Skeletal muscle (during exercise only): skeletal muscle during exercise regulate its blood flow with the help of myogenic stretch receptors (pressure related) and vasodilator metabolites like lactate. In resting muscle, flow is controlled mainly by the sympathetic nervous system (alpha-1 and beta-2 receptors). 4) Renal blood flow: blood flow to the kidney is also commonly considered as autoregulation even though neuronal and hormonal influences partially control it. During hypertension, renal afferents will constrict and maintains its blood flow to the kidney. Chronically, it will lead to hypertensive nephropathy. 5) Cutaneous blood flow: heat causes vasodilation and cold temperature causes vasoconstriction. During fever and exercise, there is an increase in heat loss which causes flushing due to vasodilation. CHANGE IN BLOOD FLOW DURING EXERCISE
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