This model is also often referred to as the classic stress response, and it revolves around the concept of homeostasis.

Pathways are required for the maintenance of homeostasis within an organism and the flux of metabolites through a pathway is regulated depending on the needs of the cell and the availability of the substrate.

The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chamical homeostasis and prevent damage to the body.

The internal thermoregulation process is one aspect of homeostasis a state of dynamic stability in an organism's internal conditions, maintained far from equilibrium with its environment (the study of such processes in zoology has been called physiological or physiological ecology).

It is via those nerves of the autonomic nervous system that the brain is able to make adjustments in the body in response to changing conditions in the environment, fluctuating emotional states, level of exercise, and other factors to maintain the body's homeostasis.