Concept
Homeostasis
Overview
In biology, homeostasis (British also homoeostasis; HOH-mee-ə-STAY-sis) is the state of steady internal physical and chemical conditions maintained by living organisms. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits (homeostatic range). Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium, and calcium ions, as well as the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.
Homeostasis is brought about by a natural resistance to change when already in its optimal conditions, and equilibrium is maintained by many regulatory mechanisms; it is thought to be the central motivation for all organic action. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control center, and an effector. The receptor is the sensing component that monitors and responds to changes in the environment, either external or internal. Receptors include thermoreceptors and mechanoreceptors. Control centers include the respiratory center and the renin-angiotensin system. An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include nuclear receptors that bring about changes in gene expression through up-regulation or down-regulation and act in negative feedback mechanisms. An example of this is in the control of bile acids in the liver.
Some centers, such as the renin–angiotensin system, control more than one variable. When the receptor senses a stimulus, it reacts by sending action potentials to a control center. The control center sets the maintenance range—the acceptable upper and lower limits—for the particular variable, such as temperature. The control center responds to the signal by determining an appropriate response and sending signals to an effector, which can be one or more muscles, an organ, or a gland. When the signal is received and acted on, negative feedback is provided to the receptor that stops the need for further signaling.
The cannabinoid receptor type 1, located at the presynaptic neuron, is a receptor that can stop stressful neurotransmitter release to the postsynaptic neuron; it is activated by endocannabinoids such as anandamide (N-arachidonoylethanolamide) and 2-arachidonoylglycerol via a retrograde signaling process in which these compounds are synthesized by and released from postsynaptic neurons, and travel back to the presynaptic terminal to bind to the CB1 receptor for modulation of neurotransmitter release to obtain homeostasis.
The polyunsaturated fatty acids are lipid derivatives of omega-3 (docosahexaenoic acid, and eicosapentaenoic acid) or of omega-6 (arachidonic acid). They are synthesized from membrane phospholipids and used as precursors for endocannabinoids to mediate significant effects in the fine-tuning adjustment of body homeostasis.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
Possible passages
Found by search and not yet checked by a person; they may only mention the idea in passing.
Similarly in the bodies of animals, those parts which carry on active functions are nitrogenous; while parts that are non-nitrogenous--as the deposits of fat--carry on no active functions. And we even find that the appearance of non-nitrogenous matter throughout tissues normally composed almost wholly of nitrogenous matter, is accompanied by loss of activity: what is called fatty degeneration being the concomitant…
Herbert Spencer, The Principles of Biology, Volume 1
States what Homeostasis is.
It is true that from the perpetual actions and reactions which are going on among all parts of the organic economy, there can be no prolonged disturbance in any one function without ultimately involving many of the others; and when once it has done so, the experiment for the most part loses its scientific value. All depends on observing the early stages of the derangement; which, unfortunately, are of necessity the…
John Stuart Mill, A System of Logic, Ratiocinative and Inductive
States what Homeostasis is.
The sensible motion constituting each visible action of an organism, is soon brought to a close by some adverse force within or without the organism. When the arm is raised, the motion given to it is antagonized partly by gravity and partly by the internal resistances consequent on structure; and its motion, thus suffering continual deduction, ends when the arm has reached a position at which the forces are…
Herbert Spencer, First Principles
Close in meaning to Homeostasis; the term itself is not named.
Related ideas
- Ancient Greek
- James Watt
- James Lovelock
- Organism
- Metabolism
- Cybernetics
- Neuron
- Oxygen
- Physics
- Jean-François Lyotard
- Gaia hypothesis
- Academic Press
- Brain
- British English
- Cell (biology)
- Chemistry
- Biology
- Information theory
Place in the tradition
Part of Dualism in cosmology.