Explain the reasons why communication between cells is essential in the human body. Use examples to illustrate your answer.

Communication is a process that involves the transfer of a signal/information from one cell to another. The main reason this has arisen between cells comes down to the basic component that makes up a human being: the eukaryotic cell. Unlike unicellular micro-organisms that can perform all the functions of life independently, the human body is composed of millions-upon-millions of cells, each of which is designated a specific function. These human cells are specialised to carry out their different roles in the body by the process of differentiation, giving rise to over 200 different cell types. For instance, a red blood cell is biconcave and lacks a nucleus to make room for haemoglobin - a tetrameric protein complex that carries oxygen throughout the circulatory system. As multicellular organisms, communication is therefore needed for such cells to coordinate themselves and work together in unison to carry out complex tasks - a phenomenon known as emergent property. As well as allowing individual cells to work together within tissues, communication is also vital in monitoring the environment both internally and externally. Because conditions are variable, it is important for cells to recognise these changes and act according to maintain their metabolic processes, otherwise known as homeostasis. The endocrine system is a perfect example to illustrate the need for communication. An endocrine gland is a collection of cells that secrete chemical messengers called hormones into the bloodstream to alter the behaviour of target cells. To maintain a constant blood sugar level, the Islets of Langerhans within the pancreas do just that. When blood glucose is high (e.g. after a meal), insulin is released to cause the uptake of excess glucose from the blood by the liver and skeletal muscle, converting them into the storage molecule glycogen. This in turn reduces the elevated glucose levels to normal.