The hormone thyroxin, for example, is secreted by an endocrine gland — your thyroid — and it needs to be distributed throughout the entire body so that it can stimulate the metabolism in all of your cells.

例如，激素甲状腺素由内分泌腺分泌——你的甲状腺——它需要分布在整个身体中，以便它可以刺激所有细胞的新陈代谢。