Introduction

Abstract

Cells of all living organisms are able to sense environmental stimuli and respond appropriately. Especially for unicellular organisms, the environment largely controls growth, metabolism, and differentiation. In higher multicellular organisms, most cells experience relative environmental homeostasis. However, growth and metabolism of cells within multicellular organisms require coordination between the cells in a tissue, an organ, and the whole organism. These cells communicate by cell-to-cell contact, gap-junctions, and integrins, or by using molecules such as hormones and growth factors, which allow cell-to-cell signalling.