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Homeostasis

In biology, homeostasis (British also homoeostasis; ) is the state of steady internal physical and chemical conditions maintained by living systems. 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 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 (CB1), located at the presynaptic neuron, is a receptor that can stop stressful neurotransmitter release to the postsynaptic neuron; it is activated by endocannabinoids (ECs) such as anandamide (N-arachidonoylethanolamide; AEA) and 2-arachidonoylglycerol (2-AG) 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 (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) are synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs) mediate significant effects in the fine-tuning adjustment of body homeostasis.

Etymology
The word homeostasis uses combining forms of homeo- and -stasis, Neo-Latin from Greek: ὅμοιος homoios, "similar" and στάσις stasis, "standing still", yielding the idea of "staying the same".

History
The concept of the regulation of the internal environment was described by French physiologist Claude Bernard in 1849, and the word homeostasis was coined by Walter Bradford Cannon in 1926. In 1932, Joseph Barcroft a British physiologist, was the first to say that higher brain function required the most stable internal environment. Thus, to Barcroft homeostasis was not only organized by the brain—homeostasis served the brain. Homeostasis is an almost exclusively biological term, referring to the concepts described by Bernard and Cannon, concerning the constancy of the internal environment in which the cells of the body live and survive. The term cybernetics is applied to technological control systems such as thermostats, which function as homeostatic mechanisms but are often defined much more broadly than the biological term of homeostasis.

Overview
The metabolic processes of all organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the interstitial fluid bathing the cells. The best-known homeostatic mechanisms in humans and other mammals are regulators that keep the composition of the extracellular fluid (or the "internal environment") constant, especially with regard to the temperature, pH, osmolality, and the concentrations of sodium, potassium, glucose, carbon dioxide, and oxygen. However, a great many other homeostatic mechanisms, encompassing many aspects of human physiology, control other entities in the body. Where the levels of variables are higher or lower than those needed, they are often prefixed with hyper- and hypo-, respectively such as hyperthermia and hypothermia or hypertension and hypotension.

If an entity is homeostatically controlled it does not imply that its value is necessarily absolutely steady in health. Core body temperature is, for instance, regulated by a homeostatic mechanism with temperature sensors in, amongst others, the hypothalamus of the brain. However, the set point of the regulator is regularly reset. For instance, core body temperature in humans varies during the course of the day (i.e. has a circadian rhythm), with the lowest temperatures occurring at night, and the highest in the afternoons. Other normal temperature variations include those related to the menstrual cycle. The temperature regulator's set point is reset during infections to produce a fever. Organisms are capable of adjusting somewhat to varied conditions such as temperature changes or oxygen levels at altitude, by a process of acclimatisation.

Homeostasis does not govern every activity in the body. For instance, the signal (be it via neurons or hormones) from the sensor to the effector is, of necessity, highly variable in order to convey information about the direction and magnitude of the error detected by the sensor. Similarly, the effector's response needs to be highly adjustable to reverse the error – in fact it should be very nearly in proportion (but in the opposite direction) to the error that is threatening the internal environment. For instance, arterial blood pressure in mammals is homeostatically controlled and measured by stretch receptors in the walls of the aortic arch and carotid sinuses at the beginnings of the internal carotid arteries. The sensors send messages via sensory nerves to the medulla oblongata of the brain indicating whether the blood pressure has fallen or risen, and by how much. The medulla oblongata then distributes messages along motor or efferent nerves belonging to the autonomic nervous system to a wide variety of effector organs, whose activity is consequently changed to reverse the error in the blood pressure. One of the effector organs is the heart whose rate is stimulated to rise (tachycardia) when the arterial blood pressure falls, or to slow down (bradycardia) when the pressure rises above the set point. Thus the heart rate (for which there is no sensor in the body) is not homeostatically controlled but is one of the effector responses to errors in arterial blood pressure. Another example is the rate of sweating. This is one of the effectors in the homeostatic control of body temperature, and therefore highly variable in rough proportion to the heat load that threatens to destabilize the body's core temperature, for which there is a sensor in the hypothalamus of the brain.

Core temperature
Mammals regulate their core temperature using input from thermoreceptors in the hypothalamus, brain, spinal cord, internal organs, and great veins. Apart from the internal regulation of temperature, a process called allostasis can come into play that adjusts behaviour to adapt to the challenge of very hot or cold extremes (and to other challenges). These adjustments may include seeking shade and reducing activity, seeking warmer conditions and increasing activity, or huddling. Behavioral thermoregulation takes precedence over physiological thermoregulation since necessary changes can be affected more quickly and physiological thermoregulation is limited in its capacity to respond to extreme temperatures.

When the core temperature falls, the blood supply to the skin is reduced by intense vasoconstriction. The blood flow to the limbs (which have a large surface area) is similarly reduced and returned to the trunk via the deep veins which lie alongside the arteries (forming venae comitantes). This acts as a counter-current exchange system that short-circuits the warmth from the arterial blood directly into the venous blood returning into the trunk, causing minimal heat loss from the extremities in cold weather. The subcutaneous limb veins are tightly constricted, not only reducing heat loss from this source but also forcing the venous blood into the counter-current system in the depths of the limbs.

The metabolic rate is increased, initially by non-shivering thermogenesis, followed by shivering thermogenesis if the earlier reactions are insufficient to correct the hypothermia.

When core temperature rises are detected by thermoreceptors, the sweat glands in the skin are stimulated via cholinergic sympathetic nerves to secrete sweat onto the skin, which, when it evaporates, cools the skin and the blood flowing through it. Panting is an alternative effector in many vertebrates, which cools the body also by the evaporation of water, but this time from the mucous membranes of the throat and mouth.

Blood glucose
Blood sugar levels are regulated within fairly narrow limits. In mammals, the primary sensors for this are the beta cells of the pancreatic islets. The beta cells respond to a rise in the blood sugar level by secreting insulin into the blood and simultaneously inhibiting their neighboring alpha cells from secreting glucagon into the blood. This combination (high blood insulin levels and low glucagon levels) act on effector tissues, the chief of which is the liver, fat cells, and muscle cells. The liver is inhibited from producing glucose, taking it up instead, and converting it to glycogen and triglycerides. The glycogen is stored in the liver, but the triglycerides are secreted into the blood as very low-density lipoprotein (VLDL) particles which are taken up by adipose tissue, there to be stored as fats. The fat cells take up glucose through special glucose transporters (GLUT4), whose numbers in the cell wall are increased as a direct effect of insulin acting on these cells. The glucose that enters the fat cells in this manner is converted into triglycerides (via the same metabolic pathways as are used by the liver) and then stored in those fat cells together with the VLDL-derived triglycerides that were made in the liver. Muscle cells also take glucose up through insulin-sensitive GLUT4 glucose channels, and convert it into muscle glycogen.

A fall in blood glucose, causes insulin secretion to be stopped, and glucagon to be secreted from the alpha cells into the blood. This inhibits the uptake of glucose from the blood by the liver, fats cells, and muscle. Instead the liver is strongly stimulated to manufacture glucose from glycogen (through glycogenolysis) and from non-carbohydrate sources (such as lactate and de-aminated amino acids) using a process known as gluconeogenesis. The glucose thus produced is discharged into the blood correcting the detected error (hypoglycemia). The glycogen stored in muscles remains in the muscles, and is only broken down, during exercise, to glucose-6-phosphate and thence to pyruvate to be fed into the citric acid cycle or turned into lactate. It is only the lactate and the waste products of the citric acid cycle that are returned to the blood. The liver can take up only the lactate, and, by the process of energy-consuming gluconeogenesis, convert it back to glucose.

Iron levels
Controlling iron levels in the body is a critically important part of many aspects of human health and disease. In humans iron is both necessary to the body and potentially harmful.

Copper regulation
Copper is absorbed, transported, distributed, stored, and excreted in the body according to complex homeostatic processes which ensure a constant and sufficient supply of the micronutrient while simultaneously avoiding excess levels. If an insufficient amount of copper is ingested for a short period of time, copper stores in the liver will be depleted. Should this depletion continue, a copper health deficiency condition may develop. If too much copper is ingested, an excess condition can result. Both of these conditions, deficiency and excess, can lead to tissue injury and disease. However, due to homeostatic regulation, the human body is capable of balancing a wide range of copper intakes for the needs of healthy individuals.

Many aspects of copper homeostasis are known at the molecular level. Copper's essentiality is due to its ability to act as an electron donor or acceptor as its oxidation state fluxes between Cu1+ (cuprous) and Cu2+ (cupric). As a component of about a dozen cuproenzymes, copper is involved in key redox (i.e., oxidation-reduction) reactions in essential metabolic processes such as mitochondrial respiration, synthesis of melanin, and cross-linking of collagen. Copper is an integral part of the antioxidant enzyme copper-zinc superoxide dismutase, and has a role in iron homeostasis as a cofactor in ceruloplasmin.

Levels of blood gases
Changes in the levels of oxygen, carbon dioxide, and plasma pH are sent to the respiratory center, in the brainstem where they are regulated. The partial pressure of oxygen and carbon dioxide in the arterial blood is monitored by the peripheral chemoreceptors (PNS) in the carotid artery and aortic arch. A change in the partial pressure of carbon dioxide is detected as altered pH in the cerebrospinal fluid by central chemoreceptors (CNS) in the medulla oblongata of the brainstem. Information from these sets of sensors is sent to the respiratory center which activates the effector organs – the diaphragm and other muscles of respiration. An increased level of carbon dioxide in the blood, or a decreased level of oxygen, will result in a deeper breathing pattern and increased respiratory rate to bring the blood gases back to equilibrium.

Too little carbon dioxide, and, to a lesser extent, too much oxygen in the blood can temporarily halt breathing, a condition known as apnea, which freedivers use to prolong the time they can stay underwater.

The partial pressure of carbon dioxide is more of a deciding factor in the monitoring of pH. However, at high altitude (above 2500 m) the monitoring of the partial pressure of oxygen takes priority, and hyperventilation keeps the oxygen level constant. With the lower level of carbon dioxide, to keep the pH at 7.4 the kidneys secrete hydrogen ions into the blood and excrete bicarbonate into the urine. This is important in acclimatization to high altitude.

Blood oxygen content
The kidneys measure the oxygen content rather than the partial pressure of oxygen in the arterial blood. When the oxygen content of the blood is chronically low, oxygen-sensitive cells secrete erythropoietin (EPO) into the blood. The effector tissue is the red bone marrow which produces red blood cells (RBCs, also called erythrocytes). The increase in RBCs leads to an increased hematocrit in the blood, and a subsequent increase in hemoglobin that increases the oxygen carrying capacity. This is the mechanism whereby high altitude dwellers have higher hematocrits than sea-level residents, and also why persons with pulmonary insufficiency or right-to-left shunts in the heart (through which venous blood by-passes the lungs and goes directly into the systemic circulation) have similarly high hematocrits.

Regardless of the partial pressure of oxygen in the blood, the amount of oxygen that can be carried, depends on the hemoglobin content. The partial pressure of oxygen may be sufficient for example in anemia, but the hemoglobin content will be insufficient and subsequently as will be the oxygen content. Given enough supply of iron, vitamin B12 and folic acid, EPO can stimulate RBC production, and hemoglobin and oxygen content restored to normal.

Arterial blood pressure
The brain can regulate blood flow over a range of blood pressure values by vasoconstriction and vasodilation of the arteries.

High pressure receptors called baroreceptors in the walls of the aortic arch and carotid sinus (at the beginning of the internal carotid artery) monitor the arterial blood pressure. Rising pressure is detected when the walls of the arteries stretch due to an increase in blood volume. This causes heart muscle cells to secrete the hormone atrial natriuretic peptide (ANP) into the blood. This acts on the kidneys to inhibit the secretion of renin and aldosterone causing the release of sodium, and accompanying water into the urine, thereby reducing the blood volume. This information is then conveyed, via afferent nerve fibers, to the solitary nucleus in the medulla oblongata. From here motor nerves belonging to the autonomic nervous system are stimulated to influence the activity of chiefly the heart and the smallest diameter arteries, called arterioles. The arterioles are the main resistance vessels in the arterial tree, and small changes in diameter cause large changes in the resistance to flow through them. When the arterial blood pressure rises the arterioles are stimulated to dilate making it easier for blood to leave the arteries, thus deflating them, and bringing the blood pressure down, back to normal. At the same time, the heart is stimulated via cholinergic parasympathetic nerves to beat more slowly (called bradycardia), ensuring that the inflow of blood into the arteries is reduced, thus adding to the reduction in pressure, and correcting the original error.

Low pressure in the arteries, causes the opposite reflex of constriction of the arterioles, and a speeding up of the heart rate (called tachycardia). If the drop in blood pressure is very rapid or excessive, the medulla oblongata stimulates the adrenal medulla, via "preganglionic" sympathetic nerves, to secrete epinephrine (adrenaline) into the blood. This hormone enhances the tachycardia and causes severe vasoconstriction of the arterioles to all but the essential organ in the body (especially the heart, lungs, and brain). These reactions usually correct the low arterial blood pressure (hypotension) very effectively.

Calcium levels
The plasma ionized calcium (Ca2+) concentration is very tightly controlled by a pair of homeostatic mechanisms. The sensor for the first one is situated in the parathyroid glands, where the chief cells sense the Ca2+ level by means of specialized calcium receptors in their membranes. The sensors for the second are the parafollicular cells in the thyroid gland. The parathyroid chief cells secrete parathyroid hormone (PTH) in response to a fall in the plasma ionized calcium level; the parafollicular cells of the thyroid gland secrete calcitonin in response to a rise in the plasma ionized calcium level.

The effector organs of the first homeostatic mechanism are the bones, the kidney, and, via a hormone released into the blood by the kidney in response to high PTH levels in the blood, the duodenum and jejunum. Parathyroid hormone (in high concentrations in the blood) causes bone resorption, releasing calcium into the plasma. This is a very rapid action which can correct a threatening hypocalcemia within minutes. High PTH concentrations cause the excretion of phosphate ions via the urine. Since phosphates combine with calcium ions to form insoluble salts (see also bone mineral), a decrease in the level of phosphates in the blood, releases free calcium ions into the plasma ionized calcium pool. PTH has a second action on the kidneys. It stimulates the manufacture and release, by the kidneys, of calcitriol into the blood. This steroid hormone acts on the epithelial cells of the upper small intestine, increasing their capacity to absorb calcium from the gut contents into the blood.

The second homeostatic mechanism, with its sensors in the thyroid gland, releases calcitonin into the blood when the blood ionized calcium rises. This hormone acts primarily on bone, causing the rapid removal of calcium from the blood and depositing it, in insoluble form, in the bones.

The two homeostatic mechanisms working through PTH on the one hand, and calcitonin on the other can very rapidly correct any impending error in the plasma ionized calcium level by either removing calcium from the blood and depositing it in the skeleton, or by removing calcium from it. The skeleton acts as an extremely large calcium store (about 1 kg) compared with the plasma calcium store (about 180 mg). Longer term regulation occurs through calcium absorption or loss from the gut.

Another example are the most well-characterised endocannabinoids like anandamide (N-arachidonoylethanolamide; AEA) and 2-arachidonoylglycerol (2-AG), whose synthesis occurs through the action of a series of intracellular enzymes activated in response to a rise in intracellular calcium levels to introduce homeostasis and prevention of tumor development through putative protective mechanisms that prevent cell growth and migration by activation of CB1 and/or CB2 and adjoining receptors.

Sodium concentration
The homeostatic mechanism which controls the plasma sodium concentration is rather more complex than most of the other homeostatic mechanisms described on this page.

The sensor is situated in the juxtaglomerular apparatus of kidneys, which senses the plasma sodium concentration in a surprisingly indirect manner. Instead of measuring it directly in the blood flowing past the juxtaglomerular cells, these cells respond to the sodium concentration in the renal tubular fluid after it has already undergone a certain amount of modification in the proximal convoluted tubule and loop of Henle. These cells also respond to rate of blood flow through the juxtaglomerular apparatus, which, under normal circumstances, is directly proportional to the arterial blood pressure, making this tissue an ancillary arterial blood pressure sensor.

In response to a lowering of the plasma sodium concentration, or to a fall in the arterial blood pressure, the juxtaglomerular cells release renin into the blood. Renin is an enzyme which cleaves a decapeptide (a short protein chain, 10 amino acids long) from a plasma α-2-globulin called angiotensinogen. This decapeptide is known as angiotensin I. It has no known biological activity. However, when the blood circulates through the lungs a pulmonary capillary endothelial enzyme called angiotensin-converting enzyme (ACE) cleaves a further two amino acids from angiotensin I to form an octapeptide known as angiotensin II. Angiotensin II is a hormone which acts on the adrenal cortex, causing the release into the blood of the steroid hormone, aldosterone. Angiotensin II also acts on the smooth muscle in the walls of the arterioles causing these small diameter vessels to constrict, thereby restricting the outflow of blood from the arterial tree, causing the arterial blood pressure to rise. This, therefore, reinforces the measures described above (under the heading of "Arterial blood pressure"), which defend the arterial blood pressure against changes, especially hypotension.

The angiotensin II-stimulated aldosterone released from the zona glomerulosa of the adrenal glands has an effect on particularly the epithelial cells of the distal convoluted tubules and collecting ducts of the kidneys. Here it causes the reabsorption of sodium ions from the renal tubular fluid, in exchange for potassium ions which are secreted from the blood plasma into the tubular fluid to exit the body via the urine. The reabsorption of sodium ions from the renal tubular fluid halts further sodium ion losses from the body, and therefore preventing the worsening of hyponatremia. The hyponatremia can only be corrected by the consumption of salt in the diet. However, it is not certain whether a "salt hunger" can be initiated by hyponatremia, or by what mechanism this might come about.

When the plasma sodium ion concentration is higher than normal (hypernatremia), the release of renin from the juxtaglomerular apparatus is halted, ceasing the production of angiotensin II, and its consequent aldosterone-release into the blood. The kidneys respond by excreting sodium ions into the urine, thereby normalizing the plasma sodium ion concentration. The low angiotensin II levels in the blood lower the arterial blood pressure as an inevitable concomitant response.

The reabsorption of sodium ions from the tubular fluid as a result of high aldosterone levels in the blood does not, of itself, cause renal tubular water to be returned to the blood from the distal convoluted tubules or collecting ducts. This is because sodium is reabsorbed in exchange for potassium and therefore causes only a modest change in the osmotic gradient between the blood and the tubular fluid. Furthermore, the epithelium of the distal convoluted tubules and collecting ducts is impermeable to water in the absence of antidiuretic hormone (ADH) in the blood. ADH is part of the control of fluid balance. Its levels in the blood vary with the osmolality of the plasma, which is measured in the hypothalamus of the brain. Aldosterone's action on the kidney tubules prevents sodium loss to the extracellular fluid (ECF). So there is no change in the osmolality of the ECF, and therefore no change in the ADH concentration of the plasma. However, low aldosterone levels cause a loss of sodium ions from the ECF, which could potentially cause a change in extracellular osmolality and therefore of ADH levels in the blood.

Potassium concentration
High potassium concentrations in the plasma cause depolarization of the zona glomerulosa cells' membranes in the outer layer of the adrenal cortex. This causes the release of aldosterone into the blood.

Aldosterone acts primarily on the distal convoluted tubules and collecting ducts of the kidneys, stimulating the excretion of potassium ions into the urine. It does so, however, by activating the basolateral Na+/K+ pumps of the tubular epithelial cells. These sodium/potassium exchangers pump three sodium ions out of the cell, into the interstitial fluid and two potassium ions into the cell from the interstitial fluid. This creates an ionic concentration gradient which results in the reabsorption of sodium (Na+) ions from the tubular fluid into the blood, and secreting potassium (K+) ions from the blood into the urine (lumen of collecting duct).

Fluid balance
The total amount of water in the body needs to be kept in balance. Fluid balance involves keeping the fluid volume stabilized, and also keeping the levels of electrolytes in the extracellular fluid stable. Fluid balance is maintained by the process of osmoregulation and by behavior. Osmotic pressure is detected by osmoreceptors in the median preoptic nucleus in the hypothalamus. Measurement of the plasma osmolality to give an indication of the water content of the body, relies on the fact that water losses from the body, (through unavoidable water loss through the skin which is not entirely waterproof and therefore always slightly moist, water vapor in the exhaled air, sweating, vomiting, normal feces and especially diarrhea) are all hypotonic, meaning that they are less salty than the body fluids (compare, for instance, the taste of saliva with that of tears. The latter has almost the same salt content as the extracellular fluid, whereas the former is hypotonic with respect to the plasma. Saliva does not taste salty, whereas tears are decidedly salty). Nearly all normal and abnormal losses of body water therefore cause the extracellular fluid to become hypertonic. Conversely, excessive fluid intake dilutes the extracellular fluid causing the hypothalamus to register hypotonic hyponatremia conditions.

When the hypothalamus detects a hypertonic extracellular environment, it causes the secretion of an antidiuretic hormone (ADH) called vasopressin which acts on the effector organ, which in this case is the kidney. The effect of vasopressin on the kidney tubules is to reabsorb water from the distal convoluted tubules and collecting ducts, thus preventing aggravation of the water loss via the urine. The hypothalamus simultaneously stimulates the nearby thirst center causing an almost irresistible (if the hypertonicity is severe enough) urge to drink water. The cessation of urine flow prevents the hypovolemia and hypertonicity from getting worse; the drinking of water corrects the defect.

Hypo-osmolality results in very low plasma ADH levels. This results in the inhibition of water reabsorption from the kidney tubules, causing high volumes of very dilute urine to be excreted, thus getting rid of the excess water in the body.

Urinary water loss, when the body water homeostat is intact, is a compensatory water loss, correcting any water excess in the body. However, since the kidneys cannot generate water, the thirst reflex is the all-important second effector mechanism of the body water homeostat, correcting any water deficit in the body.

Blood pH

The plasma pH can be altered by respiratory changes in the partial pressure of carbon dioxide; or altered by metabolic changes in the carbonic acid to bicarbonate ion ratio. The bicarbonate buffer system regulates the ratio of carbonic acid to bicarbonate to be equal to 1:20, at which ratio the blood pH is 7.4 (as explained in the Henderson–Hasselbalch equation). A change in the plasma pH gives an acid–base imbalance. In acid–base homeostasis there are two mechanisms that can help regulate the pH. Respiratory compensation a mechanism of the respiratory center, adjusts the partial pressure of carbon dioxide by changing the rate and depth of breathing, to bring the pH back to normal. The partial pressure of carbon dioxide also determines the concentration of carbonic acid, and the bicarbonate buffer system can also come into play. Renal compensation can help the bicarbonate buffer system. The sensor for the plasma bicarbonate concentration is not known for certain. It is very probable that the renal tubular cells of the distal convoluted tubules are themselves sensitive to the pH of the plasma. The metabolism of these cells produces carbon dioxide, which is rapidly converted to hydrogen and bicarbonate through the action of carbonic anhydrase. When the ECF pH falls (becoming more acidic) the renal tubular cells excrete hydrogen ions into the tubular fluid to leave the body via urine. Bicarbonate ions are simultaneously secreted into the blood that decreases the carbonic acid, and consequently raises the plasma pH. The converse happens when the plasma pH rises above normal: bicarbonate ions are excreted into the urine, and hydrogen ions released into the plasma.

When hydrogen ions are excreted into the urine, and bicarbonate into the blood, the latter combines with the excess hydrogen ions in the plasma that stimulated the kidneys to perform this operation. The resulting reaction in the plasma is the formation of carbonic acid which is in equilibrium with the plasma partial pressure of carbon dioxide. This is tightly regulated to ensure that there is no excessive build-up of carbonic acid or bicarbonate. The overall effect is therefore that hydrogen ions are lost in the urine when the pH of the plasma falls. The concomitant rise in the plasma bicarbonate mops up the increased hydrogen ions (caused by the fall in plasma pH) and the resulting excess carbonic acid is disposed of in the lungs as carbon dioxide. This restores the normal ratio between bicarbonate and the partial pressure of carbon dioxide and therefore the plasma pH. The converse happens when a high plasma pH stimulates the kidneys to secrete hydrogen ions into the blood and to excrete bicarbonate into the urine. The hydrogen ions combine with the excess bicarbonate ions in the plasma, once again forming an excess of carbonic acid which can be exhaled, as carbon dioxide, in the lungs, keeping the plasma bicarbonate ion concentration, the partial pressure of carbon dioxide and, therefore, the plasma pH, constant.

Cerebrospinal fluid
Cerebrospinal fluid (CSF) allows for regulation of the distribution of substances between cells of the brain, and neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope.

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 taken in through nutrition needs to match the amount of energy used. To achieve energy homeostasis appetite is regulated by two hormones, grehlin and leptin. Grehlin stimulates hunger and the intake of food and leptin acts to signal satiety (fullness).

A 2019 review of weight-change interventions, including dieting, exercise and overeating, found that body weight homeostasis could not precisely correct for "energetic errors", the loss or gain of calories, in the short-term.

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.

Biosphere
In the Gaia hypothesis, James Lovelock stated that the entire mass of living matter on Earth (or any planet with life) functions as a vast homeostatic superorganism that actively modifies its planetary environment to produce the environmental conditions necessary for its own survival. In this view, the entire planet maintains several homeostasis (the primary one being temperature homeostasis). Whether this sort of system is present on Earth is open to debate. However, some relatively simple homeostatic mechanisms are generally accepted. For example, it is sometimes claimed that when atmospheric carbon dioxide levels rise, certain plants may be able to grow better and thus act to remove more carbon dioxide from the atmosphere. However, warming has exacerbated droughts, making water the actual limiting factor on land. When sunlight is plentiful and the atmospheric temperature climbs, it has been claimed that the phytoplankton of the ocean surface waters, acting as global sunshine, and therefore heat sensors, may thrive and produce more dimethyl sulfide (DMS). The DMS molecules act as cloud condensation nuclei, which produce more clouds, and thus increase the atmospheric albedo, and this feeds back to lower the temperature of the atmosphere. However, rising sea temperature has stratified the oceans, separating warm, sunlit waters from cool, nutrient-rich waters. Thus, nutrients have become the limiting factor, and plankton levels have actually fallen over the past 50 years, not risen. As scientists discover more about Earth, vast numbers of positive and negative feedback loops are being discovered, that, together, maintain a metastable condition, sometimes within a very broad range of environmental conditions.

Predictive
Predictive homeostasis is an anticipatory response to an expected challenge in the future, such as the stimulation of insulin secretion by gut hormones which enter the blood in response to a meal. This insulin secretion occurs before the blood sugar level rises, lowering the blood sugar level in anticipation of a large influx into the blood of glucose resulting from the digestion of carbohydrates in the gut. Such anticipatory reactions are open loop systems which are based, essentially, on "guess work", and are not self-correcting. Anticipatory responses always require a closed loop negative feedback system to correct the 'over-shoots' and 'under-shoots' to which the anticipatory systems are prone.

Other fields
The term has come to be used in other fields, for example:

Risk
An actuary may refer to risk homeostasis, where (for example) people who have anti-lock brakes have no better safety record than those without anti-lock brakes, because the former unconsciously compensate for the safer vehicle via less-safe driving habits. Previous to the innovation of anti-lock brakes, certain maneuvers involved minor skids, evoking fear and avoidance: Now the anti-lock system moves the boundary for such feedback, and behavior patterns expand into the no-longer punitive area. It has also been suggested that ecological crises are an instance of risk homeostasis in which a particular behavior continues until proven dangerous or dramatic consequences actually occur.

Stress
Sociologists and psychologists may refer to stress homeostasis, the tendency of a population or an individual to stay at a certain level of stress, often generating artificial stresses if the "natural" level of stress is not enough.

Jean-François Lyotard, a postmodern theorist, has applied this term to societal 'power centers' that he describes in The Postmodern Condition, as being 'governed by a principle of homeostasis,' for example, the scientific hierarchy, which will sometimes ignore a radical new discovery for years because it destabilizes previously accepted norms.

Technology
Familiar technological homeostatic mechanisms include:
 * A thermostat operates by switching heaters or air-conditioners on and off in response to the output of a temperature sensor.
 * Cruise control adjusts a car's throttle in response to changes in speed.
 * An autopilot operates the steering controls of an aircraft or ship in response to deviation from a pre-set compass bearing or route.
 * Process control systems in a chemical plant or oil refinery maintain fluid levels, pressures, temperature, chemical composition, etc. by controlling heaters, pumps and valves.
 * The centrifugal governor of a steam engine, as designed by James Watt in 1788, reduces the throttle valve in response to increases in the engine speed, or opens the valve if the speed falls below the pre-set rate.

Society and Culture
The use of sovereign power, codes of conduct, religious and cultural practices and other dynamic processes in a society can be described as a part of an evolved homeostatic system of regularizing life and maintaining an overall equilibrium that protects the security of the whole from internal and external imbalances or dangers. Healthy civic cultures can be said to have achieved an optimal homeostatic balance between multiple contradictory concerns such as in the tension between respect for individual rights and concern for the public good, or that between governmental effectiveness and responsiveness to the interests of citizens.

title: Homeostasis


text:
Hockey

Hockey is a term used to denote a family of various types of both summer and winter team sports which originated on either an outdoor field, sheet of ice, or dry floor such as in a gymnasium. While these sports vary in specific rules, numbers of players, apparel, and playing surface, they share broad characteristics of two opposing teams using a stick to propel a ball or disk into a goal.

There are many types of hockey. Some games make the use of skates, either wheeled or bladed, while others do not. In order to help make the distinction between these various games, the word hockey is often preceded by another word i.e. field hockey, ice hockey, roller hockey, rink hockey, or floor hockey.

In each of these sports, two teams play against each other by trying to manoeuvre the object of play, either a type of ball or a disk (such as a puck), into the opponent's goal using a hockey stick. Two notable exceptions use a straight stick and an open disk (still referred to as a puck) with a hole in the center instead. The first case is a style of floor hockey whose rules were codified in 1936 during the Great Depression by Canada's Sam Jacks. The second case involves a variant which was later modified in roughly the 1970s to make a related game that would be considered suitable for inclusion as a team sport in the newly emerging Special Olympics. The floor game of gym ringette, though related to floor hockey, is not a true variant due to the fact that it was designed in the 1990s and modelled off of the Canadian ice skating team sport of ringette, which was invented in Canada in 1963. Ringette was also invented by Sam Jacks, the same Canadian who codified the rules for the open disk style of floor hockey 1936.

Certain sports which share general characteristics with the forms of hockey, but are not generally referred to as hockey include lacrosse, hurling, camogie, and shinty.

Etymology
The first recorded use of the word hockey is in the 1773 book Juvenile Sports and Pastimes, to Which Are Prefixed, Memoirs of the Author: Including a New Mode of Infant Education by Richard Johnson (Pseud. Master Michel Angelo), whose chapter XI was titled "New Improvements on the Game of Hockey". The belief that hockey was mentioned in a 1363 proclamation by King Edward III of England is based on modern translations of the proclamation, which was originally in Latin and explicitly forbade the games "Pilam Manualem, Pedivam, & Bacularem: & ad Canibucam & Gallorum Pugnam". The English historian and biographer John Strype did not use the word "hockey" when he translated the proclamation in 1720, instead translating "Canibucam" as "Cambuck"; this may have referred to either an early form of hockey or a game more similar to golf or croquet.

The word hockey itself is of unknown origin. One supposition is that it is a derivative of hoquet, a Middle French word for a shepherd's stave. The curved, or "hooked" ends of the sticks used for hockey would indeed have resembled these staves, and similar folk etymologies exist for the bat-and-ball sports of Croquet and Cricket. Another supposition derives from the known use of cork bungs (stoppers), in place of wooden balls to play the game. The stoppers came from barrels containing "hock" ale, also called "hocky".

Modern usage

In most of the world, the term hockey when used without clarification refers to field hockey, while in Canada, the United States, Russia and most of Eastern and Northern Europe, the term usually refers to ice hockey.

In more recent history, the word "hockey" is used in reference to either the summer Olympic sport of field hockey, which is a stick and ball game, and the winter ice team skating sports of bandy and ice hockey. This is due to the fact that field hockey and other stick and ball sports and their related variants preceded games which would eventually be played on ice with ice skates, namely bandy and ice hockey, as well as sports involving dry floors such as roller hockey and floor hockey. However, the "hockey" referred to in common parlance often depends on locale, geography, and the size and popularity of the sport involved. For example, in Europe, "hockey" more typically refers to field hockey, whereas in Canada, it typically refers to ice hockey. In the case of bandy, the game was initially called "hockey on the ice" and preceded the organization and development of ice hockey, but was officially changed to "bandy" in the early 20th century in order to avoid confusion with ice hockey, a separate sport. Bandy, while related to other hockey games, derives some of its inspiration from Association football.

Sledge hockey, a variant of ice hockey designed for players with physical disabilities, was created in the 1960s and has since been renamed, "Para-ice hockey".

History

Games played with curved sticks and a ball can be found in the histories of many cultures. In Egypt, 4000-year-old carvings feature teams with sticks and a projectile, hurling dates to before 1272 BC in Ireland, and there is a depiction from approximately 600 BC in Ancient Greece, where the game may have been called (κερητίζειν) because it was played with a horn or horn-like stick (, κέρας). In Inner Mongolia, the Daur people have been playing beikou, a game similar to modern field hockey, for about 1,000 years.

Most evidence of hockey-like games during the Middle Ages is found in legislation concerning sports and games. The Galway Statute enacted in Ireland in 1527 banned certain types of ball games, including games using "hooked" (written "hockie", similar to "hooky") sticks.

"...at no tyme to use ne occupye the horlinge of the litill balle with hockie stickes or staves, nor use no hande ball to play withoute walles, but only greate foote balle"

"Bandy, ». a game, like that of Golf, in which the ad- verse parties endeavour to beat a ball (generally a knob or gnarl from the trunk of a tree,) opposite ways...the stick with which the game is played is crook'd at the end."

By the 19th century, the various forms and divisions of historic games began to differentiate and coalesce into the individual sports defined today. Organizations dedicated to the codification of rules and regulations began to form, and national and international bodies sprang up to manage domestic and international competition.

Bandy

Bandy is played with a ball on a football pitch-sized ice arena (bandy rink), typically outdoors, and with many rules similar to association football. It is played professionally in Russia and Sweden. The sport is recognized by the IOC; its international governing body is the Federation of International Bandy.

Bandy has its roots in England in the 19th century, was originally called "hockey on the ice", and spread from England to other European countries around 1900; a similar Russian sport can also be seen as a predecessor and in Russia, bandy is sometimes called "Russian hockey". Bandy World Championships have been played since 1957 and Women's Bandy World Championships since 2004. There are national club championships in many countries and the top clubs in the world play in the Bandy World Cup every year.

Field hockey

Field hockey is played on gravel, natural grass, or sand-based or water-based artificial turf, with a small, hard ball approximately 73 mm (2.9 in) in diameter. The game is popular among both men and women in many parts of the world, particularly in Europe, Asia, Australia, New Zealand, South Africa, and Argentina. In most countries, the game is played between single-sex sides, although they can be mixed-sex.

The governing body is the 126-member International Hockey Federation (FIH). Men's field hockey has been played at each Summer Olympic Games since 1908 except for 1912 and 1924, while women's field hockey has been played at the Summer Olympic Games since 1980.

Modern field hockey sticks are constructed of a composite of wood, glass fibre or carbon fibre (sometimes both) and are J-shaped, with a curved hook at the playing end, a flat surface on the playing side and a curved surface on the rear side. All sticks are right-handed – left-handed sticks are not permitted.

While field hockey in its current form appeared in mid-18th century England, primarily in schools, it was not until the first half of the 19th century that it became firmly established. The first club was created in 1849 at Blackheath in south-east London. Field hockey is the national sport of Pakistan. It was the national sport of India until the Ministry of Youth Affairs and Sports declared in August 2012 that India has no national sport.

Ice hockey

Ice hockey is played between two teams of skaters on a large flat area of ice, using a three-inch-diameter (76.2 mm) vulcanized rubber disc called a puck. This puck is often frozen before high-level games to decrease the amount of bouncing and friction on the ice. The game is played all over North America, Europe and to varying extents in many other countries around the world. It is the most popular sport in Canada, Finland, Latvia, the Czech Republic, and Slovakia. Ice hockey is the national sport of Latvia and the national winter sport of Canada. Ice hockey is played at a number of levels, by all ages.

The governing body of international play is the 77-member International Ice Hockey Federation (IIHF). Men's ice hockey has been played at the Winter Olympics since 1924, and was in the 1920 Summer Olympics. Women's ice hockey was added to the Winter Olympics in 1998. North America's National Hockey League (NHL) is the strongest professional ice hockey league, drawing top ice hockey players from around the globe. The NHL rules are slightly different from those used in Olympic ice hockey over many categories. International ice hockey rules were adopted from Canadian rules in the early 1900s.

The contemporary sport developed in Canada from European and native influences. These included various stick and ball games similar to field hockey, bandy and other games where two teams push a ball or object back and forth with sticks. These were played outdoors on ice under the name "hockey" in England throughout the 19th century, and even earlier under various other names. In Canada, there are 24 reports of hockey-like games in the 19th century before 1875 (five of them using the name "hockey"). The first organized and recorded game of ice hockey was played indoors in Montreal, Quebec, Canada, on March 3, 1875, and featured several McGill University students.

Ice hockey sticks are long L-shaped sticks made of wood, graphite, or composites with a blade at the bottom that can lie flat on the playing surface when the stick is held upright and can legally curve either way, for left- or right-handed players.

Para ice hockey
Ice sledge hockey, or "para ice hockey", is a form of ice hockey designed for players with physical disabilities affecting their lower bodies. Players sit on double-bladed sledges and use two sticks; each stick has a blade at one end and small picks at the other. Players use the sticks to pass, stickhandle and shoot the puck, and to propel their sledges. The rules are very similar to IIHF ice hockey rules.

Canada is a recognized international leader in the development of sledge hockey, and much of the equipment for the sport was first developed there, such as sledge hockey sticks laminated with fiberglass, as well as aluminum shafts with hand-carved insert blades and special aluminum sledges with regulation skate blades.

Inline sledge hockey
Based on ice sledge hockey, inline sledge hockey is played to the same rules as inline puck hockey (essentially ice hockey played off-ice using inline skates). There is no classification point system dictating who can play inline sledge hockey, unlike the situation with other team sports such as wheelchair basketball and wheelchair rugby. Inline sledge hockey is being developed to allow everyone, regardless of whether they have a disability or not, to complete up to world championship level based solely on talent and ability.

The first game of organized inline sledge hockey was played at Bisley, Surrey, England, on December 19, 2009, between the Hull Stingrays and the Grimsby Redwings. Matt Lloyd is credited with inventing inline sledge hockey, and Great Britain is seen as the international leader in the game's development.

Roller hockey (inline)

Though inline hockey is considered a variant of roller hockey a.k.a. "rink hockey", it was derived from ice hockey instead and uses a type of hockey puck or a ball. Both roller games use a type of wheeled skate but inline hockey uses inline skates rather than roller skates or "quads".

The puck-based inline variant is more commonly played in North America than Europe while the ball-based variant is more popular in Europe.

Inline hockey puck variant is played by two teams, consisting of four skaters and one goalie, on a dry rink divided into two halves by a center line, with one net at each end of the rink. The game is played in three 15-minute periods with a variation of the ice hockey off-side rule. Icings are also called, but are usually referred to as illegal clearing. The governing body is the International Ice Hockey Federation (IIHF), just as it is for ice hockey, but some leagues and competitions do not follow the IIHF regulations, in particular USA Inline and Canada Inline.

Roller hockey (quad)

Roller hockey, also known as "quad hockey", "international-style ball hockey", "rink hockey" and "Hoquei em Patins", is an overarching name for a roller sport that uses quad skates. It has existed long before the invention of inline skates. The sport is played in over sixty countries and has a worldwide following. Roller hockey was a demonstration sport at the 1992 Barcelona Summer Olympics.

Street hockey
Also known as road hockey, this is a dry-land variant of ice and roller hockey played year-round on a hard surface (usually asphalt). A ball is usually used instead of a puck, and protective equipment is not usually worn.

Other forms of hockey
Other games derived from hockey or its predecessors include the following:
 * Air hockey is played indoors with a puck on an air-cushion table.
 * Beach hockey, a variation of street hockey, is a common sight on Southern California beaches.
 * Ball hockey is played in a gym using sticks and a ball, often a tennis ball with the felt removed.
 * Box hockey is a schoolyard game played by two people. The object of the game is to move a hockey puck from the center of the box out through a hole placed at the end of the box (known as the goal). The players kneel facing one another on either side of the box, and each attempts to move the puck to the hole on their left.
 * Broomball is played on an ice hockey rink, but with a ball instead of a puck and a "broom" (actually a stick with a small plastic implement on the end) in place of the ice hockey stick. Instead of skates, special shoes are used that have very soft rubbery soles to maximize grip while running around.
 * Deck hockey is traditionally played by the Royal Navy on ships' decks, using short wooden L-shaped sticks.
 * Floor hockey: a variety of games with different codes usually played on foot on a flat, smooth floor surface, usually indoors in gymnasiums or similar spaces.
 * Floorball is a form of hockey played in a gymnasium or in a sports hall. A whiffle ball is used instead of a plastic ball, and the sticks are only one meter long and made from composite materials.
 * Foot hockey or sock hockey is played using a bald tennis ball or rolled-up pair of socks and using only the feet. It is popular in elementary schools in the winter.
 * Gena is a field hockey sport played in Ethiopia, with which the Ethiopian Christmas festival shares its name. The equipment consists of a strong stick curved at one end, and a ball of two kinds: either called srur (made out of a rounded piece of hard-wood) or tsng (made by weaving a long strip of leather into a rounded shape).
 * Gym ringette is the off-ice floor variant of the ice skating team sport of ringette rather than ice hockey. It is not a direct variant of the style of floor hockey which helped inspire ringette.
 * Gym hockey a.k.a. floor hockey is a form of ice hockey played in a gymnasium. It uses sticks with foam ends and a foam ball or a plastic puck.
 * Hurling and Camogie are Irish games bearing some resemblance to – and notable differences from – hockey.
 * Indoor hockey is an indoor variant of field hockey.
 * Mini hockey (or knee-hockey), also known as "mini-sticks" is a form of hockey played in the United States and Canada in the basements of houses. Players kneel, or crouch, and use a miniature plastic stick, usually about 15 inches (38 cm) long, to manoeuvre a small ball or a soft, fabric-covered mini puck into miniature goals. In England 'mini hockey' refers to a seven-a-side version of field hockey for younger players, played on an area equivalent to half a normal pitch.
 * Nok Hockey is a table-top version of hockey played with no defence and a small block in front of the goal.
 * Pond hockey is a simplified form of ice hockey played on naturally frozen ice.
 * Power hockey is a form of hockey for persons requiring the use of an electric (power) wheelchair in daily life.
 * Ringette is primarily a variant of an early 20th century style of floor hockey, but played on ice hockey skates and designed for female players; it uses a straight stick and an air-filled rubber ring in place of a floor hockey puck (open disk). Though played on ice hockey rinks, the rules and strategy differ considerably from those of ice hockey and bear a closer resemblance to basketball. It should not be confused with gym ringette which is the floor variant of the ice sport.
 * Rink bandy and rinkball are team sports of Scandinavian origin. Both were influenced by bandy, but are played on ice hockey rinks and involve fewer players on each team.
 * Rossall hockey is a variation played at Rossall School on the sea shore in the winter months. Its rules are a mix of field hockey, rugby and the Eton wall game.
 * Shinny is an informal version of ice hockey.
 * Shinty is a Scottish game now played primarily in the Highlands
 * Skater hockey is a variant of inline hockey, played with a ball.
 * Spongee is a cross between ice hockey and broomball and is most popular in Manitoba, Canada. A stick and puck are used as in hockey (the puck is a softer version called a "sponge puck"), and the same soft-soled shoes are worn as in broomball. The rules are basically the same as for ice hockey, but one variation has an extra player on the ice called a "rover".
 * Table hockey is played indoors on a table.
 * Underwater hockey is played with a weighted puck on the bottom of a swimming pool.
 * Underwater ice hockey is similar to underwater hockey but played with floating puck on the underside of a frozen swimming pool.
 * Unicycle hockey is played on a hard surface using unicycles as the method of player movement. There is generally no dedicated goalkeeper.

Protection

 * Shoulder pads
 * Genital protection, a jockstrap with cup pocket and protective cup or a "jill" for female players.
 * Hockey stick

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Hockey


text:
Hawick

Hawick (Haaick; Hamhaig) is a town in the Scottish Borders council area and historic county of Roxburghshire in the east Southern Uplands of Scotland. It is 10 mi south-west of Jedburgh and 8.9 mi south-south-east of Selkirk. It is one of the furthest towns from the sea in Scotland, in the heart of Teviotdale, and is the biggest town in Roxburghshire. The town is at the confluence of the Slitrig Water with the River Teviot.

The town was formally established in the 16th century, but was previously the site of historic settlement going back hundreds of years. By the late 17th century, the town began to grow significantly, especially during the Industrial Revolution and Victorian era as a centre for the production of textiles, with a focus on knitting and weaving, involving materials such as tweed and cashmere. By the late 20th century, textile production had declined but the town remains an important regional centre for shopping, tourism and services. Hawick's architecture is distinctive in that it has many sandstone buildings with slate roofs. The town has several museums, parks and heritage sites. The town hosts the annual Alchemy Film and Moving Image Festival.

History
The name Hawick is Old English in origin, first recorded in 1167 and translates as "enclosed farm" or "enclosed hamlet". The origin of the name of Hawick was first researched in the 1860s by James Murray, a local teacher and later the primary editor of the Oxford English Dictionary. The town has a long history of habitation being settled at the confluence of Slitrig Water and the River Teviot. The west end of the town contains "the Motte", the remains of a likely 12th century Scoto-Norman motte-and-bailey castle.

On 20 June 1342, as Alexander Ramsay of Dalhousie according to the duty of his office as Sheriff of Teviotsdale was holding court in the church of Hawick, William Douglas, Lord of Liddesdale came with an armed retinue and entered the church. He was courteously welcomed. Douglas and his men attacked Ramsay and dragged him bleeding and in chains to Hermitage Castle; It is generally assumed because Douglas believed he should be Sheriff of Teviotdale. There Ramsay was imprisoned in a dungeon where he died of starvation.

The origin of Hawick being formally declared a town are said to originate with the Battle of Hornshole which was fought in 1514 between an English raiding party and young locals from Hawick. In 2014, on the 500th anniversary of the battle, some 1,800 children dressed in period costumes re-enacted the battle. The oldest official document of the town is a deed dated 11 October 1537 in which the town was re-declared a free burgh since time immemorial.

St Mary's and Old Parish Church is the oldest church in the town, being constructed in 1764 on the site of an earlier 13th century church. The church was extensively damaged by fire in the late 19th century but was reconstructed in a similar style. The cemetery contains 17th and 18th century gravestones, as well as an elaborate ironwork memorial gate given by the town council.

Hawick developed in the late 18th and 19th centuries as an important town in the manufacture of textiles and knitwear. The first knitting machines were brought to Hawick in 1771 by John Hardie, building on an existing carpet manufacturing trade and with a view to expanding into the production of stockings. As a result of a decline in the stocking trade by 1815, some weaving manufacturers had set up in the town using resources from the stocking trade. These industries continued to grow in size, when in the early 1830s, the term "Tweed" originated from the town as a result of a miscommunication of twill for the River Tweed. The town subsequently focused on the manufacturer of different textiles, hosiery and knitwear, including cashmere, adapting to different patterns and materials as fashions changed. In the 1930s, over 1200 persons were employed in producing knitwear in the town. However, by the late 20th century, changing production methods, costs and tastes resulted in the decline of the textile industries to all but a few small businesses.

July 2020 saw the start of work on a £92m flood-defence scheme. But in October 2021, with engineering work still in progress, the town was severely affected by heavy rainfall and subsequent flooding.

Governance
Local government services for Hawick are provided by Scottish Borders Council. There is also a community council covering the town.

Hawick was designated a burgh of regality in 1669 and became a police burgh in 1868. Hawick Town Hall on the High Street was built in 1886, designed by James Campbell Walker in the Scottish baronial style.

When elected county councils were created in 1890 under the Local Government (Scotland) Act 1889, the burgh of Hawick was deemed capable of running its own affairs and so was excluded from the jurisdiction of Roxburghshire County Council. Further local government reform in 1930 brought the burgh of Hawick within the area controlled by the county council, with the town being reclassified as a small burgh, ceding most of its functions to the county council.

In 1975 local government across Scotland was reformed under the Local Government (Scotland) Act 1973. The burghs and counties were abolished as administrative areas, replaced with a two-tier system of upper-tier regions and lower-tier districts. Hawick therefore became part of the Roxburgh district within the Borders region. Roxburgh District Council used Hawick Town Hall as its headquarters. Further local government reform in 1996 abolished the regions and districts, since when Hawick has been administered by Scottish Borders Council.

Monuments
Hawick High Street has an equestrian statue at the east end, known as "the Horse", erected in 1914. Drumlanrig's Tower, now a museum, dates largely from the mid-16th century.

In 2009 another monument the Turning of the Bull (artist, Angela Hunter, Innerleithen) was unveiled in Hawick. This monument depicts William Rule turning the wild bull as it was charging King Robert the Bruce, thus saving the king's life and beginning the Scottish Clan of Turnbull. A poem written by John Leyden commemorates this historical event. "His arms robust the hardy hunter flung around his bending horns, and upward wrung, with writhing force his neck retorted round, and rolled the panting monster to the ground, crushed, with enormous strength, his bony skull; and courtiers hailed the man who turned the bull."

Economy
The companies William Lockie, Hawick Cashmere, Hawick Knitwear, Johnstons of Elgin, Lyle & Scott, Peter Scott, Pringle of Scotland, and Scott and Charters, have had and in many cases still have manufacturing plants in Hawick, producing luxury cashmere and merino wool knitwear. Engineering firm Turnbull and Scott had their headquarters in an Elizabethan-style listed building on Commercial Road before moving to Burnfoot.

In recent times, unemployment has been an issue in Hawick. The rate of unemployment exceeded the average for the Scottish Borders between 2014 and 2017. The closure of once-significant employers, including mills like Peter Scott's and Pringle's have reduced the number of jobs in the town. The population has declined partly because of this; at 13,730 in 2016, it was at its lowest since the 1800s. Despite efforts to improve the economic situation, unemployment and poverty remain relatively high, with the number of children living in poverty in the town one-tenth higher than the average for the Borders region in 2017. Developments such as a new business centre, which opened in 2024, an Aldi supermarket, and distillery, which opened in 2018–19, have benefitted Hawick. Despite this, continued business closures, for example that of Homebase and the Original Factory Store in 2018, suggest continued economic decline for the town.

Transport
Hawick lies in the centre of the valley of the Teviot. The A7 Edinburgh–Carlisle road passes through the town, with main roads also leading to Berwick-upon-Tweed (the A698) and Newcastle upon Tyne (the A6088, which joins the A68 at the Carter Bar, 16 mi south-east of Hawick).

The town lost its rail service in 1969, when, as part of the Beeching Axe, the Waverley Route from Carlisle to Edinburgh via Hawick railway station was closed. It was then said to be the farthest large town from a railway station in the United Kingdom, but this changed as a result of the opening of the Borders Railway, which, in 2015, reopened part of the former Waverley Route to Tweedbank, near Galashiels. Regular buses serve the railway station at Carlisle, 42 mi away. Reconnecting Hawick to the Borders Railway would require reinstatement of a further approximately 17 mi of the former Waverley Route from Hawick to Tweedbank station via Hassendean, St Boswells and Melrose, with refurbishment of the four-arch Ale Water viaduct near New Belses. Hawick station was on the north bank of the river Teviot, below Wilton Hill Terrace, with a now demolished viaduct (near the Mart Street bridge) carrying the route south towards Carlisle. Waverley Walk in Hawick is a footpath along the former railway route, north-eastward from the former station site near Teviotdale Leisure Centre. A feasibility study is now underway to evaluate the possible reopening of the southern section of the former Waverley railway to link the Borders Railway terminus at Tweedbank through Hawick to Carlisle.

The nearest major airports are at Edinburgh, 57 mi away, and Newcastle, 56 mi away.

Culture and traditions
The town hosts the annual Common Riding, which combines the annual riding of the boundaries of the town's common land with the commemoration of a victory of local youths over an English raiding party in 1514. In March 2007, this was described by the Rough Guide publication World Party as one of the best parties in the world.

People from Hawick call themselves "Teries", after a traditional song which includes the line "Teribus ye teri odin".

Hawick and surrounding border residents are known to possess a dialect and accent slightly different from broader Scots, being classed as Southern Scots or Borders Scots. For example, the term a "Hawick Gill" is a large measure of spirits, equivalent to 0.28 litre (half a pint).

Film
Hawick is home to Alchemy Film & Arts, and its internationally renowned flagship annual event Alchemy Film and Moving Image Festival. Investing in film "as a means of generating discussion, strengthening community, and stimulating creative thought", Alchemy works with artists and communities within Hawick and the Scottish Borders on a year-round basis.

In summer 2019, Alchemy launched its award-winning Film Town project, which "aims to work to the benefit of Hawick and its unique communities by widening accessibility and inclusion for audiences, participants and partners, and by challenging social, physical and communication barriers... while contributing to Hawick's economic regeneration through an investment in its cultural identity".

In response to the COVID-19 pandemic, Alchemy delivered the tenth and eleventh editions of its annual film festival as livestream events delivered from Hawick, and assisted in helping the town's communities to digitise their own services, including the production of virtual lectures for the town's 164-year-old Hawick Archaeological Society.

Sports
The town is the home of Hawick Rugby Football Club which was founded in 1873. The town has a senior football team, Hawick Royal Albert, who currently play in the East of Scotland Football League.

The Hawick baw game was once played here by the "uppies" and the "doonies" on the first Monday after the new moon in the month of February. The river of the town formed an important part of the pitch. Although no longer played at Hawick, it is still played at nearby Jedburgh.

Confectionery
Hawick balls or baws, also known as Hills Balls or taffy rock bools, are a peppermint-flavoured boiled sweet that originated in the town. They are particularly associated with rugby commentator Bill McLaren who was known to offer them from a bag that he always carried. They are now produced in Greenock.

Community facilities
Hawick Library is a Carnegie funded library that opened in 1904.

Teviotdale Leisure Centre is the local public fitness centre, with a gym, children's soft-play area and swimming pool. The previous public baths, now disused were built in 1913 on Commercial Road and closed in the 1980s.

The Borders Textile Towerhouse is a local museum focusing on the history of textiles in Hawick and the Borders area. Examples of temporary exhibitions held include an exhibit on fashion designer Bernat Klein and a history of shops in the town. The museum occupies a restored heritage building, formerly a hotel and inn which incorporates Drumlanrig Tower, a 16th century fortified tower.

Wilton Lodge Park is a large public park in the south-west of the town. The park is home to Hawick Museum, a public museum focusing on art and local history. The museum includes local artwork, some of which was produced by members of Hawick Art Club.

The Borders Abbeys Way passes through Hawick. A statue of the popular rugby commentator Bill McLaren (1923–2010) is in Wilton Lodge Park, to the west of the town centre.

In October 2021, the local council began construction of a new £2m footbridge to link local communities, as part of a broader improvements in the town to create an improved travel network in Hawick, alongside a new flood protection scheme.

Hospital
Hawick Community Hospital is the local hospital for the area, itself replacing Hawick Cottage Hospital in 2005.

Education
Hawick High School is a non-denominational secondary school in the town. In September 2021, it was announced that a new circa £49 million will be built to replace the current school on its existing site by 2027.

Media
Local news and television programmes are provided by BBC Scotland and ITV Border. Television signals are received from the Selkirk TV transmitter and the local relay transmitter.

Local radio stations are BBC Radio Scotland on 93.5 FM, Greatest Hits Radio Scottish Borders and North Northumberland on 96.8 FM and TD9 Radio, an online community based station which broadcast from the town.

The town is served by its own local newspaper, The Hawick Paper. Other newspapers that cover the town are The Border Telegraph and Southern Reporter.

Town twinning

 * 🇫🇷 Bailleul, Nord, France

Arts

 * Dame Isobel Baillie (1895–1983), singer
 * Brian Balfour-Oatts (born 1966), art dealer
 * Brian Bonsor (1926–2011), composer
 * Andrew Cranston (born 1969), artist
 * William Landles (1923–2016), artist
 * Sir John Blackwood McEwen, composer
 * Peter McRobbie (born 1943), actor
 * Will H. Ogilvie (1869–1963), Border poet
 * Anne Redpath (1895–1965), artist
 * John Renbourn (1944–2015), musician
 * Henry Scott Riddell (1798–1870), writer
 * Francis George Scott (1880–1958), composer
 * Douglas Veitch (born 1960), musician

Journalism

 * Bill McLaren (1923–2010), sports journalist

Science

 * James Paris Lee (1831–1904), arms designer
 * Sir Andrew Smith (1797–1872), zoologist
 * Sir David Wallace (born 1945), physicist

Sports

 * Sir Chay Blyth (born 1940), yachtsman
 * Stuart Easton (born 1983), motorcycle racer
 * Darcy Graham (born 1997), rugby player
 * Jimmie Guthrie (1897–1937), motorcycle racer
 * Steve Hislop (1962–2003), motorcycle racer
 * Stuart Hogg (born 1992), rugby player
 * Matt Leyden (1904–1975), ice hockey executive
 * Robert Lindsay-Watson (1886–1956), athlete
 * Jim Renwick (born 1952), rugby player
 * Tony Stanger (born 1968), rugby player
 * James Storrie (1885–1951), cricket player
 * Walter Storrie (1875–1945), cricket player
 * Dave Valentine (1926–1976), rugby player
 * Rory Sutherland (born 1992), rugby player

Politics and public life

 * John Daykins VC MM (1883–1933), decorated British Army sergeant of the First World War
 * Helen Wilson Fell was born here in 1849 and became a leading suffragist and philanthropist in Sydney
 * Nigel Griffiths (born 1955), politician
 * Tom Jenkins (1797–1859) the United Kingdom's first black schoolteacher
 * Alison Suttie, Baroness Suttie (born 1968), politician
 * Francis Walsingham (1577–1647), English Jesuit priest, who assumed the name John Fennell
 * James Wilson (1805–1860), businessman and politician

Business

 * John Inglis (1823–1898), Hawick-born and raised Canadian manufacturer of engines and consumer products

 * James Alison (1862-1932), Dalkeith (Eskbank) born architect practising in Hawick

title: Hawick


text:
Hatfield, Hertfordshire

Hatfield is a town and civil parish in Hertfordshire, England, in the borough of Welwyn Hatfield. It had a population of 29,616 in 2001, 39,201 at the 2011 Census, and 41,265 at the 2021 Census. The settlement is of Saxon origin. Hatfield House, home of the Marquess of Salisbury, forms the nucleus of the old town. From the 1930s when de Havilland opened a factory, until the 1990s when British Aerospace closed it, aircraft design and manufacture employed more people there than any other industry. Hatfield was one of the post-war New Towns built around London and has much modernist architecture from the period. The University of Hertfordshire is based there.

Hatfield lies 20 mi north of London beside the A1(M) motorway and has direct trains to London King's Cross railway station, London St Pancras railway station, Finsbury Park and Moorgate. There has been a strong increase in commuters who work in London moving into the area.

In 2022, TV property expert Phil Spencer named Hatfield as the second best place to live for regular commuters to London, based on train times, house prices and the attractions the town has.

History
In the early tenth century Hatfield belonged to a vir potens (powerful man) called Ordmær and his wife Ealde, who may have been the grandfather of King Edward the Martyr. Sometime between 932 and 956 he exchanged the town for land in Devon with Æthelstan Half-King, who then gave it to his sons. King Edgar seized the land when he became king on 959, claiming that Ordmær and Ealde had bequeathed it to him, but Æthelstan's sons recovered it after Edgar died. Hatfield is recorded in Domesday Book of 1086 as the property of the Abbey of Ely, and unusually the original census data that compilers of Domesday used survives, giving us slightly more information than in the final Domesday record. No other records remain until 1226, when Henry III granted the Bishops of Ely rights to an annual four-day fair and a weekly market. The town was then called Bishop's Hatfield.

Hatfield House is the seat of the Cecil family, the Marquesses of Salisbury. Elizabeth Tudor was confined there for three years in what is now known as The Old Palace in Hatfield Park. Legend has it that she learnt here of her accession as queen in 1558 while sitting under an oak tree in the Park. She held her first Council in the Great Hall (The Old Palace) of Hatfield. In 1851 the route of the Great North Road (now the A1000) was altered to avoid cutting through the grounds of Hatfield House.

The town grew up around the gates of Hatfield House. Old Hatfield retains many historic buildings, notably the Old Palace, St Etheldreda's Church and Hatfield House. The Old Palace was built by the Bishop of Ely, Cardinal Morton, in 1497, during the reign of Henry VII, and the only surviving wing is still used today for Elizabethan-style banquets.

St Etheldreda's Church was founded by the monks from Ely, and the first wooden church, built in 1285, was probably sited where the existing building stands overlooking the old town.

The church of St Etheldreda, well situated towards the top of the hill, contains an Early English round arch with dog-tooth moulding, but for the rest is Decorated and Perpendicular and largely restored. The chapel north of the chancel is known as the Salisbury chapel and was erected by Robert Cecil, 1st Earl of Salisbury, who was buried here. It is in a combination of classic and Gothic styles. In a private portion of the churchyard is buried, among others of the family, Robert Gascoyne-Cecil, 3rd Marquess of Salisbury.

Aerospace industry

In 1930 the de Havilland airfield and aircraft factory was opened at Hatfield and by 1949 it had become the largest employer in the town, with almost 4,000 staff. It was taken over by Hawker Siddeley in 1960 and merged into British Aerospace in 1978. In the 1930s it produced a range of small biplanes. During the Second World War it produced the Mosquito fighter bomber and developed the Vampire, the second British production jet aircraft after the Gloster Meteor. After the war, facilities were expanded and it developed the Comet airliner (the world's first production jet liner), the Trident airliner, and an early bizjet, the DH125.

British Aerospace closed the Hatfield site in 1993 having moved the BAe 146 production line to Woodford Aerodrome. The land was used as a film set for Steven Spielberg's movie Saving Private Ryan and most of the BBC/HBO television drama Band of Brothers. It was later developed for housing, higher education, commerce and retail.

Today, Hatfield's aviation history is remembered by the names of certain local streets and pubs (e. g. Comet Way, The Airfield, Dragon Road) as well as The Comet Hotel (now owned by Ramada) built in the 1930s. The Harrier Pub (formerly The Hilltop) is actually named after the Harrier bird, not the aircraft, hence the original pub sign showing the bird. The de Havilland Aircraft Heritage Centre, at Salisbury Hall in nearby London Colney, preserves and displays many historic de Havilland aeroplanes and related archives.

New Town
The Abercrombie Plan for London in 1944 proposed a New Town in Hatfield. It was designated in the New Towns Act 1946 (9 & 10 Geo. 6. c. 68), forming part of the initial Hertfordshire group with nearby Stevenage, Welwyn Garden City and Hemel Hempstead. The Government allocated 2340 acre for Hatfield New Town, with a population target of 25,000. (By 2001 the population had reached 27,833. ) The Hatfield Development Corporation, tasked with creating the New Town, chose to build a new town centre, rejecting Old Hatfield because it was on the wrong side of the railway, without space for expansion and "with its intimate village character, out of scale with the town it would have to serve." They chose instead St Albans Road on the town's east–west bus route. A road pattern was planned that offered no temptation to through traffic to take short cuts through the town and which enabled local traffic to move rapidly.

Hatfield retains New Town characteristics, including much modernist architecture of the 1950s and the trees and open spaces that were outlined in the original design. As of 2017, a redevelopment of the town centre was planned.

Governance
There are three tiers of local government covering Hatfield, at parish, district and county level: Hatfield Town Council, Welwyn Hatfield Borough Council and Hertfordshire County Council. Hatfield Town Council has its offices and meeting place at the Birchwood Leisure Centre on Longmead. Hatfield town council is currently under a Labour administration led by Cllr Larry Crofton.

From 1894 until 1974 the lower two tiers of local government were Hatfield Parish Council and Hatfield Rural District Council. The rural district council built itself a headquarters at 16 St Albans Road East in 1930. The rural district council was abolished in 1974 and its powers transferred to Welwyn Hatfield.

Hatfield is twinned with the Dutch port town of Zierikzee. Hatfield is part of the Welwyn Hatfield constituency, which also includes Welwyn Garden City. The Member of Parliament (MP) for Welwyn Hatfield is Grant Shapps, a Conservative.

Sport
Hatfield Town F.C. plays Non-League football at Gosling Sports Park. The Welwyn Garden City Hockey Club are a field hockey club based in Hatfield.

Hatfield Athletic Football Club competes in the Herts Senior County League and plays its games at Lemsford.

The town has a public swimming pool and four sports/leisure centres (two with indoor swimming pools).

Climate
Hatfield experiences an oceanic climate (Köppen climate classification Cfb) like most of the United Kingdom.

Culture and recreation

Hatfield has a nine-screen Odeon cinema, a stately home (Hatfield House), a museum (Mill Green Museum), a contemporary art gallery (Art and Design Gallery), a theatre (The Weston Auditorium) and a music venue (The Forum Hertfordshire). There are shopping centres in the new town: the Galleria (indoor shopping centre), The Stable Yard (Hatfield House), and three supermarkets (ASDA, ALDI and Tesco). In 2022, Hatfield held its first vegan market, an event held in a number of English towns, at Hatfield House and now holds the market each June and November. During Veganuary in 2023, students at the University of Hertfordshire organized their own vegan market.

Education
Hatfield contains numerous primary and secondary schools, including St Philip Howard Catholic Primary School, Howe Dell Primary School, Countess Anne School, Onslow St Audrey's School, Bishop's Hatfield Girls' School and the independent day and private boarding girls' school Queenswood School (only to name a few).

In addition to the important areas in the town, the University of Hertfordshire is also included by many. A large section of the airfield site was purchased by the university and the £120-million de Havilland Campus, incorporating a £15-million Sports Village, was opened in September 2003. The university has closed its sites at Watford and Hertford; faculties situated there have been moved to the de Havilland Campus.

The equine branch of the Royal Veterinary College is based in Hatfield.

Places of interest

 * Hatfield House
 * Hatfield War Memorial
 * The Forum Hertfordshire (music venue) University of Hertfordshire. In 2011, the music video for Ed Sheeran's Lego House, featuring Harry Potter's Rupert Grint, was filmed in Hatfield. Filming took place at The Forum venue, located on University of Hertfordshire, College Lane campus. Filming of the video took place during Sheeran's performance at the venue on 8 October 2011. Many students were involved during filming, as they made up most of the audience at the Forum that day.
 * Mill Green Museum and watermill
 * Art and Design Gallery (contemporary art gallery) University of Hertfordshire
 * The Weston Auditorium (theatre and cinema) University of Hertfordshire
 * The Galleria
 * Hatfield Business Park, the former de Havilland plant, later BAE Systems Hatfield, was used as a location for Saving Private Ryan (film) and Band of Brothers (TV series).

Transport
Hatfield is 20 mi to the north of London. It is 14 mi from London Luton Airport. The A1(M) runs through a tunnel beneath the town, which is also close to the M25.

In the eighteenth and nineteenth centuries it was the northern terminus of the Hatfield and Reading Turnpike that allowed travelers from the north to continue their journey to the west without going through the congestion of London.

The East Coast railway line from London to York runs through the town, separating the old and new parts. A commuter service connects Hatfield railway station to London King's Cross. A new railway station and car park opened in late 2015. The frequent train service runs direct from Hatfield Station to London King's Cross (21 minutes) via Finsbury Park (16 minutes, Victoria Underground Line) on fast trains running two or three times an hour. An additional train service calls at all stations to Moorgate in the City of London.

Hatfield is well served by buses with regular services to all nearby towns and villages and as far as north London. Bus services are run by Uno, Arriva and Centrebus who are all part of the local Intalink Partnership.

The Hatfield rail crash occurred in October 2000, which brought track-maintenance deficiencies to public attention. A garden beside the East Coast Main Line was built as a memorial to the crash victims.

Local media
The local TV stations are BBC London & ITV London, received from the Crystal Palace TV transmitter and the Hemel Hempstead relay transmitter. BBC East and ITV Anglia are also received from the Sandy Heath TV transmitter.

Local radio stations are BBC Three Counties Radio on 90.4 FM, Heart Hertfordshire on 106.9 and Radio Verulam on 92.6 FM.

The Welwyn Hatfield Times is the town's local weekly newspaper.

Business

 * Michael Birch (born 1970), founder of the social network BEBO, lived in Hatfield.
 * Geoffrey de Havilland (1882–1965), founder of De Havilland Aircraft Company
 * Jack Olding (Henry John Douglas Olding, fl. mid-20th c.), wartime tank and tractor importer, came from Hatfield.

Music and dance

 * Babe Ruth, a 1970s rock band, came from Hatfield.
 * Colin Blunstone (born 1945), of the Zombies lived in Hatfield.
 * Martin Carthy (born 1941), folk musician, was born in Hatfield.
 * Sandra Conley (born 1943), principal dancer with the Royal Ballet.
 * Donovan (born 1946), folk musician, moved to Hatfield at the age of 10 and spent the rest of his childhood there.
 * Barbara Gaskin (born 1950), pop singer, No. 1 with "It's My Party".
 * George Martin (1926–2016), record producer for the Beatles, lived in Hatfield in the 1950s.
 * Alan Shacklock (born 1950), pop musician and record producer, lived in Hatfield.
 * Sal Solo (Christopher Scott Stevens, born 1961), rock singer, was born in Hatfield.
 * Mick Taylor (born 1949), Rolling Stones guitarist 1969–1974, grew up in Hatfield.
 * Tracey Thorn (born 1962), lead singer of Everything But The Girl, was born in Hatfield and attended Bishop's Hatfield Girls' School.

Politics, nobility and royalty

 * Robert Cecil, 1st Earl of Salisbury (c. 1563–1612), statesman
 * Robert Cecil, 3rd Marquess of Salisbury (1830–1903), Conservative politician, lived at Hatfield House and was buried at St Etheldreda Church.
 * Robert Gascoyne-Cecil, 5th Marquess of Salisbury (1893–1972), Conservative politician
 * William Lamb, 2nd Viscount Melbourne (1779–1848), prime minister, was buried at St Etheldreda Church.
 * Henry John Temple, 3rd Viscount Palmerston (1784–1865), prime minister
 * Elizabeth Tudor (1533–1603), future queen, lived at Hatfield House (Hatfield Old Palace)
 * Malcolm Wicks (1947–2012), Labour Party politician and Minister for Energy, was born in Hatfield

Religion

 * Walter Curle (1575–1647), Bishop of Winchester and a close supporter of William Laud, was born in Hatfield.
 * John Morton (c. 1420–1500), Cardinal and Bishop of Ely, built Hatfield Old Palace.

Science and scholarship

 * L. H. Sumanadasa (1910–1986), aviator and university founder, learned to fly at Hatfield.
 * John Tradescant the elder (c. 1570s–1638), botanist, gardener and naturalist, was head gardener at Hatfield House
 * Michael Ventris (1922-1956), deciphered Linear B script, died in Hatfield in a motor accident

Sports

 * Keith Abbis (born 1932), Brighton and Hove Albion footballer
 * Samir Carruthers (born 1993), Sheffield United footballer, is from Hatfield.
 * Matthew Connolly (born 1987), QPR defender, lived and attended primary school in Hatfield.
 * Iain Dowie (born 1965), West Ham player, QPR manager & BBC pundit, was born and raised in Hatfield and studied mechanical engineering at the University of Hertfordshire.
 * Valentine Faithfull (1820–1894), first-class cricketer and clergyman, was born in Hatfield.
 * Rodney Marsh (born 1944), QPR footballer, is from Hatfield.
 * Francis Pember (1862–1954), first-class cricketer, was born in Hatfield.
 * Billy Joe Saunders (born 1989), WBO middleweight world champion boxer
 * Korey Smith (born 1991) Bristol City footballer was born and grew up in Hatfield

Stage, media and film

 * Sanjeev Bhaskar (born 1963), comedian and broadcaster, lived in Hatfield whilst studying at the University of Hertfordshire.
 * John Cazabon (1914–1983), actor on stage, screen and radio, was born in Hatfield.
 * Pippa Haywood (born 1961), television, stage and radio actress, was born in Hatfield.
 * Diane-Louise Jordan (born 1960), television presenter, grew up in Hatfield.
 * David Kossoff (1919–2005), broadcaster and father of Paul Kossoff of the 1960s rock band Free, lived in Hatfield.
 * Derek Martin (born 1933), actor known especially for role of Charlie Slater in EastEnders
 * Gerry Northam (born 1947), radio presenter and investigative journalist, was born in Hatfield.
 * Guy Ritchie (born 1968), film director famous for Snatch and Lock, Stock and Two Smoking Barrels, was born in Hatfield.
 * Letitia Dean, born in Hatfield.

Writing

 * Moniza Alvi (born 1954), poet and writer, grew up in Hatfield.
 * Barbara Cartland (1901–2000), author of romances, lived in Hatfield.
 * Geoffrey Drage (1860–1955), non-fiction writer and politician, was born in Hatfield.
 * Nathaniel Lee (c. 1653–1692), poet and playwright, was born in Hatfield, where his father was rector.

Nearby towns and villages

 * Bell Bar
 * Borehamwood
 * Brookmans Park
 * Colney Heath
 * Hertford
 * Lemsford, village within Hatfield civil parish
 * Letty Green
 * London Colney
 * Newgate Street, village within Hatfield civil parish
 * Potters Bar
 * St Albans
 * Stevenage
 * Watford
 * Welham Green
 * Welwyn Garden City

title: Hatfield, Hertfordshire