Well, insulin is a protein, it's produced by cells in the pancreas, it circulates in your blood.

胰岛素是一种蛋白质,由胰腺细胞分泌,随着血液不断在体内循环

耶鲁公开课 - 生物医学工程探索课程节选

It also turns out that they're made stable in these environments like milk and mucus secretions because of this secretory chain which is wrapped around it.

同时,连接抗体还可以,使抗体在像乳汁或是粘液分泌物,这样的体内环境中保持稳定,因为分泌循环系统可以将抗体包裹在内

耶鲁公开课 - 生物医学工程探索课程节选

When they do that, this insulin then starts to circulate throughout the blood.

当胰岛素开始分泌后,胰岛素就开始通过血液来循环

耶鲁公开课 - 生物医学工程探索课程节选

A small molecule gets produced by cells in one part of the body, circulates in the blood, estrogen enters cells, and sometimes that estrogen is able to penetrate deep within the cell, even into the nucleus.

雌激素是由身体某部分细胞分泌的,随着血液循环进入细胞,有时雌激素能够进入到细胞内部,甚至进入到细胞核内

耶鲁公开课 - 生物医学工程探索课程节选