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What Is Homeostasis?

Homeostatic Balance

The body is a complex system in which several biological processes are performed by cells that rely on homeostasis in order to properly function.

The body has the ability to physiologically regulate its internal environment with response to fluctuations that occur in the internal or external environment through homeostasis. Homeostasis refers to a state of constant equilibrium within the cells, tissues, organs, and fluids of the body. The body requires a stable, constant internal environment for the many processes that occur to keep the organism functioning. For example, animals need a balance of ions circulating in their blood systems to prevent blood pH values from increasing or decreasing.

The mechanical operation of a thermostat can be considered analogous to the body's own temperature regulation. The thermostat responds to temperature changes in the room by signaling the air conditioner (or heater) to either turn on or off. The temperature of the home is maintained within a narrow range by this system. Biological systems are more complex, but the mechanisms maintaining internal temperature within a narrow range are similar. Internal temperature regulation is one facet of homeostasis.

The process of maintaining homeostasis is complex. It has an effect on the function of multiple body systems and several organs play a role in maintaining homeostasis. These include the liver, kidneys, and brain. Specifically, the liver works to maintain the metabolic processing of carbohydrates and toxic substances constantly entering the body from the external environment. The kidneys function to maintain blood fluid volume and acid levels in the blood. The brain regulates homeostasis through the hypothalamus region of the brain and the glands of the endocrine system. Homeostatic disruption can occur when the body systems are unable to maintain balance. This inability to maintain balance, also referred to as homeostatic imbalance, will affect normal functions in the body, leading to a disease, disorder, or even death. One common example is hypothyroidism in which the body fails to produce or regulate thyroid hormones properly. The result of failed thyroid hormone homeostasis includes weight gain, lack of concentration, and fatigue. Diabetes is another condition resulting in homeostatic imbalance. People with diabetes have pancreas glands that do not produce sufficient quantities of insulin, a hormone required for the homeostatic control of blood glucose levels.

Understanding the Homeostatic Process

Homeostatic processes include three components: receptors to detect changing conditions, the brain to direct responses to the change, and effectors (muscles or glands) that respond to the brain's directions.
Homeostatic regulation functions to keep the body at a steady state around a narrow range of values. The set point is a value where the physiological state of the body is stable. There are normal fluctuations that occur away from the set point, which means the body's systems must function to constantly move these values as close as possible to this set point. In order to make these changes, the body must be able to sense a stimulus (plural, stimuli), which is a change in the internal or external environment contributing to fluctuations that occur away from the set point.
The body must maintain its internal environment within a narrow range of values, called the set point. For any variable, such as body temperature or concentration of substance, the ideal body value is the ideal state the variable should be maintained at for proper body function. The upper body values of the wave reflect the body's response to counteract an increase that is above the ideal body value. The same concept applies to the lower body value.
All homeostatic systems have three common structural elements. This includes a receptor (sense organ), control center (the brain), and effector (muscle or gland). When a stimulus, external or internal, is recognized by a receptor it sends information indicative of a deviation from homeostasis to the control center. The control center processes the information, and in turn, sends instructions to the effector muscle or gland. The effector muscle or gland responds to these instructions from the control center to restore homeostasis, which was originally disrupted by the stimulus. In the case of body temperature, temperature sensing nerves in the skin send information about the external environment to the brain. In addition, receptors in the hypothalamus region of the brain monitor the temperature of the blood passing through the brain. The brain interprets the information from these two sources to determine whether body temperature is deviating too far from the set point. If the brain determines the body temperature needs adjustment, it sends instructions initiating physiological and behavioral changes to adjust the body temperature back to the set point. Physiologic changes may include shivering or sweating, while behavioral changes may include seeking shelter or removing a jacket.
Receptors (sense organs), the control center (brain), and effectors (muscles or glands) are three structural elements that work together to respond and maintain homeostasis.
Homeostatic imbalances can occur due to the inability of the body to respond to a stimulus. There are two basic ways this type of imbalance occurs—deficiency or toxicity. Deficiency occurs because normal operational pathways in the body are blocked, causing an inadequate quantity of vitamins or minerals to be available to cells for use. Toxicity occurs when excess ions are present in the bloodstream, creating poisonous conditions for the cell. In both cases, whether a deficiency or toxicity, cells are affected. For example, high levels of uric acid (normally excreted by kidneys) can result in a disease called hyperuricemia.