On the smooth muscle cells controlling some blood vessels, there are receptors called alpha receptors — when norepinephrine, or epinephrine, bind to those receptors, they make those smooth muscle cells contract, thereby restricting blood flow.

在控制一些血管的平滑肌细胞上，有一种叫做α受体的受体——当去甲肾上腺素或肾上腺素与这些受体结合时，它们使这些平滑肌细胞收缩，从而限制血液流动。

And you also learned that the same messenger chemical can evoke different responses depending on the receptors, with alpha receptors causing smooth muscles to constrict, for example, while beta receptors cause smooth muscle to relax.

你还了解到，同样的信使化学物质可以根据受体唤起不同的反应，例如，α受体导致平滑肌收缩，而β受体导致平滑肌放松。