The genome encodes the information needed to make us human, but genes do not directly cause growth and development. Gene expression is regulated and mediated by several biological systems, especially the neurological and endocrine (neuroendocrine) systems. Hormones regulate and coordinate critical developmental processes, integrating across several systems, including the central nervous system, the reproductive system, and the digestive system. Hormones are influenced by nutritional status and infections. Therefore, hormones provide a mechanism by which “real-time” information about a body’s health is communicated to the brain and processed by its regulatory centers in the hypothalamus and pituitary, through which growth is affected accordingly.