Homeostasis and Control Systems in Organisms

In evolutionary history, each species has developed a specific internal environment setup at various levels of organization to suit its external environment. Despite continuous fluctuations in the external environment, organisms resist and manage these changes by making adjustments to maintain narrow fluctuations within their internal environment, thus protecting it from harm. This process is known as homeostasis, which uses various control systems to keep internal fluctuations in check compared to wider external fluctuations.

The most vulnerable components of the internal environment that may be affected by external fluctuations are water, solutes, and temperature. Additionally, the mechanism by which an organism eliminates harmful nitrogenous wastes depends on water availability. This process is called osmoregulation, which regulates the balance of solutes and water, while excretion refers to the elimination of nitrogenous waste, and thermoregulation maintains internal temperature within tolerable limits.

Similarly, control systems operate at the cellular level to regulate the intracellular and extracellular internal environment of an organism. Fluctuations in the intracellular environment, within the cell membrane, are kept within a narrow range compared to the extracellular environment (vascular and other interstitial fluids). In addition to solutes and water, essential metabolites, hormones, and other components are also maintained within required ranges. Homeostasis does not imply a fixed internal environment, as changes within a specific range are necessary for normal body functions. For example, while water availability in the external environment may vary greatly from abundant supply to almost dry conditions, the quantity of water in the internal environment may also fluctuate within a narrow range in response. The control systems prevent the body from being flooded with water in abundance or dehydrated in dry conditions. Furthermore, adaptation to lower or higher levels of internal range in response to drastic external fluctuations is beneficial for the organism to maintain a sense of normalcy.

Homeostasis, controlling systems lower fluctuations in internal environments

The living control systems for homeostasis function similarly to physical control systems, consisting of three components: receptors, control center, and effectors. In a physical control system, such as a temperature control system, a sensor (thermometer) detects temperature changes from a set point and signals the control center to take action, such as switching on heaters or cooling units to adjust the temperature. Similarly, in living systems, there is a set point for temperature regulation in endothermic animals. Receptors detect changes in temperature and signal the control center for action, either activating cooling or heating systems accordingly. This process of detecting changes and signaling for effector responses is known as feedback mechanism. In these processes, there is an inverse effectors' response to changes in the external environment, with cooling effectors responding to warmth and vice versa, which is referred to as negative feedback. Please refer to the image below for a visual representation.