The human body typically has a variety of regulatory processes that can maintain a balance of internal conditions. Body temperature, respiration, digestion, and reflexes are examples of homeostatic responses that can occur to offset internal changes. Respiratory rate and body temperature, for example, often remain at a specific level called a set point. This is often true of the ability of the kidneys to regulate the body’s sodium levels. Homeostatic responses are typically regulated by the release of hormones, neurotransmitters, and other chemical substances from cells in response to biological changes.
When internal equilibrium is changed, a receptor can detect the cause and generate a signal, while this afferent input is picked up by an integrating center. Signals are received here, which can be a part of the brain or other structure in the central nervous system. The process of moving an output signal to the response, or effector, is called the efferent pathway. A series of reactions involving substances that are passed on between cells, from cells into the blood stream, or into fluid in body cavities often constitutes the trigger for homeostatic responses.
One type of human homeostasis is the regulation of internal temperature. If the body gets cold, the nerves in the skin can trigger homeostatic responses that act on muscles, which constrict blood flow. If less blood passes through the area, then usually less heat is lost. Other muscular signals can cause shivering, which usually generates heat in the body.
The body can also regulate the carbohydrates and fats it stores. In response to eating, drinking, and even breathing, the compounds stored, used, or excreted as waste can be regulated internally. Homeostatic responses to nutrients in the body often include the metabolism of substances from other compounds, like the production of many proteins derived from various other molecules.
Reflexes are homeostatic responses that can serve to protect the body from potentially harmful stimuli. Rapidly moving away from something hot is usually automatic, while moving a car away from a road hazard when driving is typically learned. Physical changes normally occur that allow the body to respond quickly if danger is perceived.
Many homeostatic responses involve conscious motion, but many occur internally without any thought. Digestion is one example, as well as the regulation of sodium in the blood by the kidneys. The organs may delay their response by adapting to an increase in salt intake, but can create an equal balance over a few days. Some scientists believe that if homeostasis is not achieved in some way, the result can be a variety of diseases and other medical conditions.