Misplaced Pages

#202797

40-522: Continuous dehydration can cause acute and chronic diseases, but is most often associated with renal and neurological disorders. Excessive thirst, called polydipsia , along with excessive urination, known as polyuria , may be an indication of diabetes mellitus or diabetes insipidus . There are receptors and other systems in the body that detect a decreased volume or an increased osmolite concentration. Some sources distinguish "extracellular thirst" from "intracellular thirst", where extracellular thirst

80-610: A 15 and 25% loss of body water. Mild dehydration usually resolves with oral rehydration , but severe cases may need intravenous fluids. Dehydration can cause hypernatremia (high levels of sodium ions in the blood). This is distinct from hypovolemia (loss of blood volume , particularly blood plasma ). Chronic dehydration can cause kidney stones as well as the development of chronic kidney disease . The hallmarks of dehydration include thirst and neurological changes such as headaches , general discomfort , loss of appetite , nausea , decreased urine volume (unless polyuria

120-421: A dehydrated state is accomplished by the replenishment of necessary water and electrolytes (through oral rehydration therapy , or fluid replacement by intravenous therapy ). As oral rehydration is less painful, non-invasive, inexpensive, and easier to provide, it is the treatment of choice for mild dehydration. Solutions used for intravenous rehydration may be isotonic , hypertonic , or hypotonic depending on

160-467: A key role in the regulation of thirst. The area postrema and nucleus tractus solitarii signal to the subfornical organ and to the lateral parabrachial nucleus . The latter signaling relies on the neurotransmitter serotonin . The signal from the lateral parabrachial nucleus is relayed to the median preoptic nucleus . The median preoptic nucleus and the subfornical organ receive signals of decreased volume and increased osmolite concentration. Finally,

200-486: A side effect from many different types of drugs and medications. In the elderly, blunted response to thirst or inadequate ability to access free water in the face of excess free water losses (especially hyperglycemia related) seem to be the main causes of dehydration. Excess free water or hypotonic water can leave the body in two ways – sensible loss such as osmotic diuresis , sweating , vomiting and diarrhea , and insensible water loss, occurring mainly through

240-497: Is contained within the cells. This consists of approximately 40% of the total body water. Fluid inside the cells has high concentrations of potassium, magnesium, phosphate, and proteins. Extracellular fluid consists of all fluid outside of the cells, and it includes blood and interstitial fluid. This makes up approximately 60% of the total body water. The most common ions in extracellular fluid include sodium, chloride, and bicarbonate. The concentration of dissolved molecules and ions in

280-401: Is established. Thirst quenching varies among animal species, with dogs, camels, sheep, goats, and deer replacing fluid deficits quickly when water is available, whereas humans and horses may need hours to restore fluid balance. The areas of the brain that contribute to the sense of thirst are mainly located in the midbrain and the hindbrain . Specifically, the hypothalamus appears to play

320-676: Is required. Fluids containing a proper balance of replacement electrolytes are given orally or intravenously with continuing assessment of electrolyte status; complete resolution is normal in all but the most extreme cases. The prognosis for dehydration depends on the cause and extent of dehydration. Mild dehydration normally resolves with oral hydration. Chronic dehydration, such as from physically demanding jobs or decreased thirst, can lead to chronic kidney disease . Elderly people with dehydration are at higher risk of confusion, urinary tract infections , falls, and even delayed wound healing. In children with mild to moderate dehydration, oral hydration

360-515: Is the cause of dehydration), confusion , unexplained tiredness , purple fingernails, and seizures . The symptoms of dehydration become increasingly severe with greater total body water loss. A body water loss of 1-2%, considered mild dehydration, is shown to impair cognitive performance. While in people over age 50, the body's thirst sensation diminishes with age, a study found that there was no difference in fluid intake between young and old people. Many older people have symptoms of dehydration, with

400-419: Is thirst generated by decreased volume and intracellular thirst is thirst generated by increased osmolite concentration. It is vital for organisms to be able to maintain their fluid levels in very narrow ranges. The goal is to keep the interstitial fluid, the fluid outside the cell, at the same concentration as the intracellular fluid, the fluid inside the cell. This condition is called isotonic and occurs when

440-422: Is typically seen in dehydration due to free water loss. A urinalysis, which is a test that performs chemical and microscopic analysis of urine, may find darker color or foul odor with severe dehydration. Urinary sodium also provides information about the type of dehydration. For hyponatremic dehydration, such as from vomiting or diarrhea, urinary sodium will be less than 10mmol/L due to increased sodium retention by

SECTION 10

#1732783759203

480-498: Is usually due to excessive sweating, disease, or a lack of access to water. Mild dehydration can also be caused by immersion diuresis , which may increase risk of decompression sickness in divers . Most people can tolerate a 3-4% decrease in total body water without difficulty or adverse health effects. A 5-8% decrease can cause fatigue and dizziness . Loss of over 10% of total body water can cause physical and mental deterioration, accompanied by severe thirst . Death occurs with

520-541: The European Food Safety Authority (EFSA) included water as a macronutrient in its dietary reference values for the first time. Recommended intake volumes in the elderly are the same as for younger adults (2.0 L/day for females and 2.5 L/day for males) as despite lower energy consumption, the water requirement of this group is increased due to a reduction in renal concentrating capacity. According to preliminary research, quenching of thirst –

560-399: The homeostatic mechanism to stop drinking – occurs via two neural phases: a "preabsorptive" phase which signals quenched thirst many minutes before fluid is absorbed from the stomach and distributed to the body via the circulation, and a "postabsorptive" phase which is regulated by brain structures sensing to terminate fluid ingestion. The preabsorptive phase relies on sensory inputs in

600-403: The median preoptic nucleus which initiates water seeking and ingestive behavior. Destruction of this part of the hypothalamus in humans and other animals results in partial or total loss of desire to drink even with extremely high salt concentration in the extracellular fluids. In addition, there are visceral osmoreceptors which project to the area postrema and nucleus tractus solitarii in

640-399: The renin angiotensin system (RAS) and is detected by cells in the kidney. When these cells detect decreased blood flow due to the low volume they secrete an enzyme called renin . Renin then enters the blood where it catalyzes a protein called angiotensinogen to angiotensin I . Angiotensin I is then almost immediately converted by an enzyme already present in the blood to the active form of

680-429: The skin and respiratory tract . In humans, dehydration can be caused by a wide range of diseases and states that impair water homeostasis in the body. These occur primarily through either impaired thirst/water access or sodium excess. Water makes up approximately 60% of the human body by mass. Within the body, water is classified as intracellular fluid or extracellular fluid. Intracellular fluid refers to water that

720-574: The brain. Because sodium is also lost from the plasma in hypovolemia, the body's need for salt proportionately increases in addition to thirst in such cases. This is also a result of the renin-angiotensin system activation. In adults over the age of 50 years, the body's thirst sensation reduces and continues diminishing with age, putting this population at increased risk of dehydration . Several studies have demonstrated that elderly persons have lower total water intakes than younger adults, and that women are particularly at risk of too low an intake. In 2009,

760-411: The cause of dehydration as well as the sodium concentration in the blood. Pure water injected into the veins will cause the breakdown ( lysis ) of red blood cells ( erythrocytes ). When fresh water is unavailable (e.g. at sea or in a desert), seawater or drinks with significant alcohol concentration will worsen dehydration. Urine contains a lower solute concentration than seawater; this requires

800-469: The cells of the body, through their membranes, to the extracellular compartment, by osmosis , thus causing cellular dehydration. Clusters of cells ( osmoreceptors ) in the organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO), which lie outside of the blood brain barrier can detect the concentration of blood plasma and the presence of angiotensin II in the blood. They can then activate

840-431: The concentration of interstitial fluid. The other set of receptors detects blood volume . This is one of two types of thirst and is defined as thirst caused by loss of blood volume (hypovolemia) without depleting the intracellular fluid. This can be caused by blood loss, vomiting, and diarrhea. This loss of volume is problematic because if the total blood volume falls too low the heart cannot circulate blood effectively and

SECTION 20

#1732783759203

880-420: The demand for water in the cell. After the animal drinks water, the interstitial fluid becomes less concentrated of solutes (more concentrated of water) than the intracellular fluid and the cell will fill with water as it tries to equalize the concentrations. This condition is called hypotonic and can be dangerous because it can cause the cell to swell and rupture. One set of receptors responsible for thirst detects

920-444: The eventual result is hypovolemic shock. The vascular system responds by constricting blood vessels thereby creating a smaller volume for the blood to fill. This mechanical solution, however, has definite limits and usually must be supplemented with increased volume. The loss of blood volume is detected by cells in the kidneys and triggers thirst for both water and salt via the renin-angiotensin system. Hypovolemia leads to activation of

960-435: The fluid is described as Osmolarity and is measured in osmoles per liter (Osm/L). When the body experiences a free water deficit, the concentration of solutes is increased. This leads to a higher serum osmolarity. When serum osmolarity is elevated, this is detected by osmoreceptors in the hypothalamus. These receptors trigger the release of antidiuretic hormone (ADH). ADH resists dehydration by increasing water absorption in

1000-610: The heat. When such large amounts of water are being lost through perspiration, electrolytes , especially sodium, are also being lost. In most athletes exercising and sweating for 4–5 hours with a sweat sodium concentration of less than 50 mmol/L, the total sodium lost is less than 10% of total body stores (total stores are approximately 2,500 mmol, or 58 g for a 70-kg person). These losses appear to be well tolerated by most people. The inclusion of sodium in fluid replacement drinks has some theoretical benefits and poses little or no risk, so long as these fluids are hypotonic (since

1040-816: The kidneys and constricting blood vessels. It acts on the V2 receptors in the cells of the collecting tubule of the nephron to increase expression of aquaporin. In more extreme cases of low blood pressure, the hypothalamus releases higher amounts of ADH which also acts on V1 receptors. These receptors cause contractions in the peripheral vascular smooth muscle. This increases systemic vascular resistance and raises blood pressure. Dehydration occurs when water intake does not replace free water lost due to normal physiologic processes, including breathing , urination , perspiration , or other causes, including diarrhea , and vomiting . Dehydration can be life-threatening when severe and lead to seizures or respiratory arrest, and also carries

1080-490: The kidneys in an effort to conserve water. In dehydrated patients with sodium loss due to diuretics or renal dysfunction, urinary sodium may be elevated above 20 mmol/L. Patients may also have elevated serum levels of blood urea nitrogen (BUN) and creatinine . Both of these molecules are normally excreted by the kidney, but when the circulating blood volume is low, the kidney can become injured. This causes decreased kidney function and results in elevated BUN and creatinine in

1120-416: The kidneys to create more urine to remove the excess salt, causing more water to be lost than was consumed from seawater. If a person is dehydrated and taken to a medical facility, IVs can also be used. For severe cases of dehydration where fainting , unconsciousness , or other severely inhibiting symptoms are present (the patient is incapable of standing upright or thinking clearly), emergency attention

1160-583: The mainstay of dehydration prevention is the replacement of free water losses). The most effective treatment for minor dehydration is widely considered to be drinking water and reducing fluid loss. Plain water restores only the volume of the blood plasma, inhibiting the thirst mechanism before solute levels can be replenished. Consumption of solid foods can also contribute to hydration. It is estimated approximately 22% of American water intake comes from food. Urine concentration and frequency will return to normal as dehydration resolves. In some cases, correction of

1200-460: The most common being fatigue. Dehydration contributes to morbidity in the elderly population, especially during conditions that promote insensible free water losses, such as hot weather. Risk factors for dehydration include but are not limited to: exerting oneself in hot and humid weather, habitation at high altitudes, endurance athletics, elderly adults, infants, children and people living with chronic illnesses. Dehydration can also come as

1240-451: The mouth, pharynx , esophagus , and upper gastrointestinal tract to anticipate the amount of fluid needed, providing rapid signals to the brain to terminate drinking when the assessed amount has been consumed. The postabsorptive phase occurs via blood monitoring for osmolality , fluid volume, and sodium balance, which are collectively sensed in brain circumventricular organs linked via neural networks to terminate thirst when fluid balance

Thirst - Misplaced Pages Continue

1280-436: The patient's body, in a location such as the forearm or the back of the hand, and watching to see how quickly it returns to its normal position. The skin turgor test can be unreliable in patients who have reduced skin elasticity, such as the elderly. While there is no single gold standard test to diagnose dehydration, evidence can be seen in multiple laboratory tests involving blood and urine. Serum osmolarity above 295 mOsm/kg

1320-415: The protein, angiotensin II . Angiotensin II then travels in the blood until it reaches the posterior pituitary gland and the adrenal cortex , where it causes a cascade effect of hormones that cause the kidneys to retain water and sodium, increasing blood pressure. It is also responsible for the initiation of drinking behavior and salt appetite via the subfornical organ . Osmometric thirst occurs when

1360-668: The risk of osmotic cerebral edema if rehydration is overly rapid. The term "dehydration" has sometimes been used incorrectly as a proxy for the separate, related condition of hypovolemia , which specifically refers to a decrease in volume of blood plasma . The two are regulated through independent mechanisms in humans; the distinction is important in guiding treatment. Common exam findings of dehydration include dry mucous membranes, dry axillae, increased capillary refill time, sunken eyes, and poor skin turgor. More extreme cases of dehydration can lead to orthostatic hypotension, dizziness, weakness, and altered mental status. Depending on

1400-469: The same levels of solutes are present on either side of the cell membrane so that the net water movement is zero. If the interstitial fluid has a higher concentration of solutes (or a lower concentration of water) than the intracellular fluid, it will pull water out of the cell. This condition is called hypertonic and if enough water leaves the cell, it will not be able to perform essential chemical functions. The animal will then become thirsty in response to

1440-498: The serum. For routine activities, thirst is normally an adequate guide to maintain proper hydration. Minimum water intake will vary individually depending on weight, energy expenditure, age, sex, physical activity, environment, diet, and genetics. With exercise, exposure to hot environments, or a decreased thirst response , additional water may be required. In athletes in competition, drinking to thirst optimizes performance and safety, despite weight loss, and as of 2010, there

1480-514: The signals are received in cortex areas of the forebrain where thirst arises. The subfornical organ and the organum vasculosum of the lamina terminalis contribute to regulating the overall bodily fluid balance by signalling to the hypothalamus to form vasopressin , which is later released by the pituitary gland . Dehydration In physiology, dehydration is a lack of total body water that disrupts metabolic processes . It occurs when free water loss exceeds free water intake. This

1520-493: The solute concentration of the interstitial fluid increases. This increase draws water out of the cells, and they shrink in volume. The solute concentration of the interstitial fluid increases by high intake of sodium in diet or by the drop in volume of extracellular fluids (such as blood plasma and cerebrospinal fluid ) due to loss of water through perspiration, respiration, urination and defecation. The increase in interstitial fluid solute concentration causes water to migrate from

1560-405: The underlying cause of dehydration, other symptoms may be present as well. Excessive sweating from exercise may be associated with muscle cramps. Patients with gastrointestinal water loss from vomiting or diarrhea may also have fever or other systemic signs of infection. The skin turgor test can be used to support the diagnosis of dehydration. The skin turgor test is conducted by pinching skin on

1600-431: Was no scientific study showing that it is beneficial to stay ahead of thirst and maintain weight during exercise. In warm or humid weather, or during heavy exertion, water loss can increase markedly, because humans have a large and widely variable capacity for sweating. Whole-body sweat losses in men can exceed 2 L/h during competitive sport , with rates of 3–4 L/h observed during short-duration, high-intensity exercise in

#202797