That cells that form tissues often have junctions that hold them together so that they don't fall apart and they exist as a solid piece of tissue.

组织细胞通常通过,细胞连接而联系在一起,所以它们不会分散开来,而保持坚固的组织形态

耶鲁公开课 - 生物医学工程探索课程节选

It refers to usually 'receptors' that are fixed in a cell, on a cell membrane, and 'ligands' which are dispersed throughout the body and free to diffuse around, and occasionally will find the cell.

受体这个词通常代表了,固定于细胞表面的分子,而配体分散于体内各处,能够自由扩散,它们偶尔会与细胞邂逅

耶鲁公开课 - 生物医学工程探索课程节选