Growth is defined as an increase in size of a body part or the organism. It is usually accomplished by increasing the number of cells. Individual cells can also increase in size when not dividing. For growth to occur constructive activities must occur at a faster rate than destructive ones. Hormones produced by the endocrine system are used to regulate and control growth and development. Hormones are chemical messengers released into the blood that are transported throughout the body. Binding of hormones to cellular receptors initiate responses that tend to be more prolonged than those induced by the nervous system. Hormonal targets include most cells of the body. The lack of a whole body coordination system would result in loss of homeostasis within the organism. Organs would be unable to coordinate their roles to carry out the systems function, timing of cell divisions would be disrupted, and the overall health of the organism would suffer.

Growth and development require the incredible coordination of literally millions of cells. What type of communication system would best serve this large-scale, whole-body process? What might be compromised if growth were regulated instead by a more immediate system?