How is oxygen consumption lowered physiologically when the body is cooled?

When the body is cooled, one of the significant physiological responses is a decrease in enzyme activity. Enzymes are vital for biochemical reactions, including those involved in metabolism and energy production. As the temperature drops, the kinetic energy of molecules decreases, leading to a reduction in reaction rates. This slowdown in metabolic processes results in a lower overall oxygen consumption, as the body requires less oxygen to support its metabolic needs at lower temperatures.

The other choices do not directly contribute to the decrease in oxygen consumption in the manner that enzyme activity does. Increased blood flow would typically enhance oxygen delivery to tissues, while relaxation of vascular tissues might not directly correlate with a decrease in oxygen requirements. Reduction in heart rate could have some impact on oxygen consumption, but it is more complex and does not inherently relate to the fundamental biochemical changes observed with decreased temperatures. Thus, the decrease in enzyme activity is a clear and direct mechanism through which oxygen consumption is lowered as the body cools.