Homeostasis

In <a href="/facts/Biology/1M1ee3pB">biology</a>, homeostasis is the state of steady internal <a href="/facts/Physics/a7aH2y08">physical</a> and <a href="/facts/Chemistry/SrNqkGVm">chemical</a> conditions maintained by <a href="/facts/Organism/j8JkL09u">living systems</a>. This is the condition of optimal functioning for the organism and includes many variables, such as <a href="/facts/Body_temperature/V692hIjw">body temperature</a> and <a href="/facts/Fluid_balance/sKmwSJ8a">fluid balance</a>, being kept within certain pre-set limits (homeostatic range). Other variables include the <a href="/facts/PH/RnSv8D7y">pH</a> of <a href="/facts/Extracellular_fluid/hzm4qatP">extracellular fluid</a>, the concentrations of <a href="/facts/Sodium/eYuSPu2V">sodium</a>, <a href="/facts/Potassium/FWPwS7Rj">potassium</a>, and <a href="/facts/Calcium/hf252CC0">calcium</a> <a href="/facts/Ion/3bePpDna">ions</a>, as well as the <a href="/facts/Blood_sugar_level/I4SkNzrm">blood sugar level</a>, 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 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 <a href="/facts/Thermoreceptor/sH49VAy0">thermoreceptors</a> and <a href="/facts/Mechanoreceptor/rj6j4Nt3">mechanoreceptors</a>. Control centers include the <a href="/facts/Respiratory_center/PPxQf431">respiratory center</a> and the <a href="/facts/Renin%25E2%2580%2593angiotensin_system/9XLt8PQL">renin-angiotensin system</a>. An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include <a href="/facts/Nuclear_receptor/9aYqKxnM">nuclear receptors</a> that bring about changes in <a href="/facts/Gene_expression/alCPohLR">gene expression</a> through up-regulation or down-regulation and act in <a href="/facts/Negative_feedback/G9byVgpN">negative feedback</a> mechanisms. An example of this is in the control of <a href="/facts/Bile_acid/ojTJzf0c">bile acids</a> in the <a href="/facts/Liver/Rtp4Fk2b">liver</a>.
Some centers, such as the <a href="/facts/Renin%25E2%2580%2593angiotensin_system/9XLt8PQL">renin–angiotensin system</a>, 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 <a href="/facts/Effector_cell/HybQCQ1n">effector</a>, which can be one or more muscles, an organ, or a <a href="/facts/Gland/gfq2of7k">gland</a>. When the signal is received and acted on, negative feedback is provided to the receptor that stops the need for further signaling.
The <a href="/facts/Cannabinoid_receptor_type_1/7b2tfePV">cannabinoid receptor type 1</a>, located at the <a href="/facts/Synapse/vdMRJCUn">presynaptic</a> <a href="/facts/Neuron/G7CyTVdH">neuron</a>, is a <a href="/facts/Receptor_(biochemistry)/tjTAC76a">receptor</a> that can stop stressful <a href="/facts/Neurotransmitter/LlpYFSU3">neurotransmitter</a> release to the postsynaptic neuron; it is activated by <a href="/facts/Cannabinoid/MHcltwTn">endocannabinoids</a> such as <a href="/facts/Anandamide/dwkXv1fC">anandamide</a> (N-arachidonoylethanolamide) and <a href="/facts/2-Arachidonoylglycerol/0avBjCr3">2-arachidonoylglycerol</a> via a <a href="/facts/Retrograde_signaling/tuSHb1Pj">retrograde signaling</a> 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 <a href="/facts/Polyunsaturated_fatty_acid/hvHwC43j">polyunsaturated fatty acids</a> are <a href="/facts/Lipid/TdQR87HX">lipid</a> derivatives of <a href="/facts/Omega-3_fatty_acid/X72Ynqov">omega-3</a> (<a href="/facts/Docosahexaenoic_acid/kwkBIrSd">docosahexaenoic acid</a>, and <a href="/facts/Eicosapentaenoic_acid/KR6qsu44">eicosapentaenoic acid</a>) or of <a href="/facts/Omega-6_fatty_acid/0o3n3dtL">omega-6</a> (<a href="/facts/Arachidonic_acid/7fMTra6z">arachidonic acid</a>). They are synthesized from <a href="/facts/Cell_membrane/vAXSD0DT">membrane</a> <a href="/facts/Phospholipid/u6GhNCF5">phospholipids</a> and used as precursors for endocannabinoids to mediate significant effects in the fine-tuning adjustment of body homeostasis.

Homeostasis open-in-new

Homeostasis