Cell regulation is a broad term used to describe the many processes that occur within a cell that are aimed at maintaining homeostasis. Homeostasis is a balanced condition in which cell avoids harmful extremes of any form through various active or passive regulatory processes. Regulation processes moderate everything from the growth and replication rates of cells to the salt levels and acidity of the cellular environment. If cell growth and replication are not moderated, cells may replicate at an uncontrollably high rate; this condition is called cancer.
A great deal of cell regulation takes place at the genetic level. Many different genes are expressed or repressed in response to environmental triggers in order to maintain the cell's homeostasis. Various proteins are able to bind to certain segments of RNA or DNA, which contain the genetic information used in gene expression, in order to repress, induce, or enhance the expression of a given gene. Genes are expressed through the production of proteins. E. Coli, for example, expresses a different set of genes by producing an abnormal set of proteins when it is exposed to high heat levels; these proteins better allow it to maintain some form of homeostasis in the case of "heat shock."
Cellular signaling is a highly important aspect of the study of cell regulation because most of the regulatory processes within a cell are a response to some form of signal. Changes in a cell's environment may cause signaling proteins or chemicals to bind to signal receptors in order to indicate the need for some form of regulatory response. Cells even communicate with other cells to prepare them for changes in the cellular environment. Communication that results in cell regulation may occur within a cell, between adjacent or touching cells, or even between distant cells. Endocrine cells, for example, are specialized cells that send chemical signals to various parts of the body in order to communicate the need for various cell regulation actions.
Many different diseases and disorders are caused by a breakdown of cell regulation processes. Cancer is caused when a cell's growth and replication are not properly regulated. Normal cells undergo apoptosis, or programmed cell death; cancerous cells do not, so they can replicate and grow indefinitely. Autoimmune disorders are also a result of failed cell regulation and signaling. Such disorders occur when the immune system fails to recognize a cell as "self" and launches an inappropriate immune attack on the harmless cell or cells.