July 5, 2022

Homeostasis or homeostasis (rare: ὅμοιοστάσις, English: homeostasis) is the tendency of living organisms to maintain a constant internal environment.


Homeostasis is one of the important properties of living organisms, and refers to the property that the state of living organisms is kept constant regardless of changes in environmental factors inside or outside the organism, or that state. In addition to being one of the requirements for living things to be living things, it is also an important factor in defining health. It is also called biological homeostasis (/ biological homeostasis action). The range in which homeostasis is maintained covers all biological functions such as body temperature, blood pressure, osmotic pressure of body fluid, hydrogen ion index, elimination of foreign substances (non-self) such as pathogenic microorganisms and viruses, and wound repair. In order to maintain homeostasis, when these changes, there must be an action to undo them, that is, a change in the direction of canceling the changes that have occurred. This is called a negative feedback effect. The diencephalic hypothalamus is mainly responsible for this action, and the autonomic nervous system and endocrine system (hormone secretion) play the role of the transmission network of the command.


Around 1859, physiologist Claude Bernard proposed that the internal environment of a living body is independent of the outside due to factors such as the circulation of tissue fluid (fixation of the internal environment). In the late 1920s and early 30s, physiologist Walter B. Cannon named it "homeostasis," which means the same state in classical Greek.

Adjustment mechanism

The homeostasis of the whole organism is maintained by multiple adjustment mechanisms.

Feedback mechanism

The hypothalamus-the endocrine system centered on the pituitary gland is regulated by a feedback mechanism to maintain various homeostasis in the body.

Buffer system

There is a mechanism to stabilize the pH of body fluids by constructing a chemical buffer system.


Body temperature homeostasis

For example, the thermoregulatory function of birds and mammals is one of biological homeostasis. For birds and mammals, the optimum temperature during activity is around 40 ° C (this temperature varies depending on the species and physiological condition). If the body temperature is higher than this, sweating will occur due to the autonomic nervous system and endocrine system, and if the body temperature is low due to dilation of skin blood vessels, shaking (chills) or non-shaking heat production (fever due to accelerated metabolism) Try to raise body temperature. Not a reflection. Body temperature rises during an infection because inflammatory substances raise the target temperature for regulation. This is a resistance activity that takes advantage of the fact that pathogens are vulnerable to heat. Antipyretic analgesics reduce fever by lowering this target temperature.

Blood glucose homeostasis

In addition, the mechanism of blood glucose regulation in the human body (blood glucose regulation mechanism) blood glucose also has homeostasis. However, the blood glucose regulation mechanism itself is related to the thermoregulatory function.

Immune homeostasis

The immune system functions with a certain balance between a system that enhances immunity to protect itself from external pathogens and an immunosuppressive system that prevents excessive immune enhancement, and this is called immune homeostasis. Living organisms have an immune system as a defense mechanism that protects themselves from external pathogens, but the immune system cannot completely distinguish between self and non-self. If the immune system is over-enhanced, the excessive inflammatory response is a substance or useful symbiotic micro that should not be considered as a pathogen or foreign body.