A MULTICELLULAR organism is a spectacular thing. Like all other multicellular beings, we have cells that co-ordinate with each other during growth to diversify into different types. The co-ordination of this process in itself is an extraordinary endeavour: the average adult human is made up of about 30 trillion human cells of around 200 types.

There are several systems by which cells respond to and produce information. Sensory organs can produce triggers, the nervous system acts as an electrically based electrical wiring for superfast connectivity, and individual cells themselves can react to physical forces or to chemicals. These signalling chemicals, most of which circulate in our blood, are known as hormones.

Any circulating chemical that triggers change can be classified as a hormone, meaning they are a diverse group of chemicals. Some trigger organ growth, and those organs then go on to produce other hormones.