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Chapter 8 : Cells Respond to Their External Environments
This chapter discusses the types of cell signals and cell receptors, examples of direct interaction between the environment and single-celled organisms, how hormones regulate the environment within multicellular organisms regulation of glucose concentration in the blood, regulation of salt and water balance and blood pressure. A key concept for the chapter is that in order for a cell (or, by extension, a multicellular organism) to respond to signals from the environment, all the steps from the signal to the effect must be in place. The chapter discusses some examples of cascades related to some of the ways our bodies regulate salt and water balance. Some basics of signaling and response are illustrated by an example from the bacterium Escherichia coli. The interconnected system of hormones that regulate body’s blood pressure and salt and water balance, and the major hormones involved in blood pressure regulation are explained. Each of these hormones has a receptor through which it exerts its effects. Taking diabetes as an example, one might assume that blood pressure regulation could be impaired by either a failure to make one of the hormones or a failure to respond to it. Kidney failure is treated with dialysis, in which blood is pumped through porous membrane tubes suspended in fluid containing healthy concentrations of salt and glucose.