Control of Blood Flow in Skeletal Muscles Local Regulation-Decreased oxygen in M

Question

Control of Blood Flow in Skeletal Muscles Local Regulation-Decreased oxygen in Muscle Greatly Enhances Flow. The tremendous increase in muscle blood flow that occurs during skeletal muscle activity is caused mainly by chemicals acting directly on the muscle arterioles to cause dilation. One of the most important chemical effects is reduction of oxygen in the muscle tissues. When muscles are active they use oxygen t rapidly, thereby decreasing the oxygen concentration in the tissue fluids. This in turn causes local arteriolar vaso- ilation because the arteriolar walls cannot maintainave contraction in the absence of oxygen and because oxy gen deficiency causes release of vasodilator substances. Adenosine may be an important vasodilator substance, but experiments have shown that even large amounts of adenosine infused directly into a muscle artery cannot increase blood flow to the same extent as during intense exercise and cannot sustain vasodilation in skeletal muscle for more than about 2 hours Fortunately, even after the muscle blood vessels have become insensitive to the vasodilator effects of adeno- sine, still other vasodilator factors continue to maintain increased capillary blood flow as long as the exercise continues. These factors include (1) potassium ions, (2) adenosine triphosphate (ATP), (3) lactic acid, and (4) carbon dioxide. We still do not know quantitatively how great a role each of these plays in increasing muscle 243

Explanation / Answer

Vasoconstriction if the narrowing of the blood vessels, especially the arteries – the large ones and the arterioles. In vasoconstriction, due to the narrowing of the blood vessels, the blood pressure increases and the blood flow decreases.

Vasodilation is the opposite of vasoconstriction. In vasodilation the veins, arteries and arterioles expand leading to more flow of blood within them due to a decrease in the vascular resistance. Vasodilation decreases blood pressure (mainly in the arterioles).

Vasodilators are agents that widen the blood vessels and therefore cause a decrease in the vascular resistance and an increase in the blood flow.

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