我们知道它们在管上涂抹了一种液体，但我们不知道它们从哪里分泌出这种液体，也不知道它的化学成分是什么。
We know they smear a liquid on the tube, but we don't know where they secrete it from or what its chemical composition is.
采取这种方式生长，平滑肌可分泌胶原，一种结构蛋白，是人体中除其它几种物质外组成血管壁的重要成分。
Grown this way, smooth muscle secretes collagen, a structural protein that is, among several other things in the body, an important component of the walls of blood vessels.
胰岛素，一种由胰腺分泌的激素，是新陈代谢过程中一种主要的成分，因为它有助于抑制血糖浓度异常地升高。
Insulin, a hormone secreted by the pancreas, is a key ingredient in the metabolic process because it helps keep the blood-sugar level from rising abnormally.
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