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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Homeostasis | 8/9 | https://en.wikipedia.org/wiki/Homeostasis | reference | science, encyclopedia | 2026-05-05T07:15:31.436253+00:00 | kb-cron |
=== Neurotransmission === Inhibitory neurons in the central nervous system play a homeostatic role in the balance of neuronal activity between excitation and inhibition. Inhibitory neurons using GABA, make compensating changes in the neuronal networks preventing runaway levels of excitation. An imbalance between excitation and inhibition is seen to be implicated in a number of neuropsychiatric disorders.
=== Neuroendocrine system ===
The neuroendocrine system is the mechanism by which the hypothalamus maintains homeostasis, regulating metabolism, reproduction, eating and drinking behaviour, energy utilization, osmolarity and blood pressure. The regulation of metabolism, is carried out by hypothalamic interconnections to other glands. Three endocrine glands of the hypothalamic–pituitary–gonadal axis (HPG axis) often work together and have important regulatory functions. Two other regulatory endocrine axes are the hypothalamic–pituitary–adrenal axis (HPA axis) and the hypothalamic–pituitary–thyroid axis (HPT axis). The liver also has many regulatory functions of the metabolism. An important function is the production and control of bile acids. Too much bile acid can be toxic to cells and its synthesis can be inhibited by activation of FXR a nuclear receptor.
=== Gene regulation ===
At the cellular level, homeostasis is carried out by several mechanisms including transcriptional regulation that can alter the activity of genes in response to changes.
=== Energy balance ===
The amount of energy consumed through dietary intake must align closely with the amount of energy expended by the body in order to maintain overall energy balance, a state known as energy homeostasis. This critical process is managed through the regulation of appetite, which is influenced by two key hormones: ghrelin and leptin. Ghrelin is known as the hunger hormone, as it plays a significant role in stimulating feelings of hunger, thereby prompting individuals to seek out and consume food. On the other hand, leptin serves a different function; it signals satiety, or the feeling of fullness, telling the body that it has consumed enough food. In a comprehensive review conducted in 2019 that examined various weight-change interventions—including dieting, exercise, and instances of overeating—it was determined that the body's mechanisms for regulating weight homeostasis are not capable of precisely correcting for energetic errors. These energetic errors refer to the notable loss or gain of calories that can occur in the short term. This research highlights the complexity of energy balance, showing that the body may struggle to adjust rapidly to fluctuations in calorie intake or expenditure, thereby complicating the process of maintaining a stable body weight in response to immediate changes in energy consumption and usage.
== Clinical significance == Many diseases are the result of a homeostatic failure. Almost any homeostatic component can malfunction either as a result of an inherited defect, an inborn error of metabolism, or an acquired disease. Some homeostatic mechanisms have inbuilt redundancies, which ensures that life is not immediately threatened if a component malfunctions; but sometimes a homeostatic malfunction can result in serious disease, which can be fatal if not treated. A well-known example of a homeostatic failure is shown in type 1 diabetes mellitus. Here blood sugar regulation is unable to function because the beta cells of the pancreatic islets are destroyed and cannot produce the necessary insulin. The blood sugar rises in a condition known as hyperglycemia. The plasma ionized calcium homeostat can be disrupted by the constant, unchanging, over-production of parathyroid hormone by a parathyroid adenoma resulting in the typically features of hyperparathyroidism, namely high plasma ionized Ca2+ levels and the resorption of bone, which can lead to spontaneous fractures. The abnormally high plasma ionized calcium concentrations cause conformational changes in many cell-surface proteins (especially ion channels and hormone or neurotransmitter receptors) giving rise to lethargy, muscle weakness, anorexia, constipation and labile emotions. The body water homeostat can be compromised by the inability to secrete ADH in response to even the normal daily water losses via the exhaled air, the feces, and insensible sweating. On receiving a zero blood ADH signal, the kidneys produce huge unchanging volumes of very dilute urine, causing dehydration and death if not treated. As organisms age, the efficiency of their control systems becomes reduced. The inefficiencies gradually result in an unstable internal environment that increases the risk of illness, and leads to the physical changes associated with aging. Various chronic diseases are kept under control by homeostatic compensation, which masks a problem by compensating for it (making up for it) in another way. However, the compensating mechanisms eventually wear out or are disrupted by a new complicating factor (such as the advent of a concurrent acute viral infection), which sends the body reeling through a new cascade of events. Such decompensation unmasks the underlying disease, worsening its symptoms. Common examples include decompensated heart failure, kidney failure, and liver failure according to Fan et al. (2011).