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Encyclopedia > Thirst

Thirst is the basic instinct of humans or animals to drink. It arises from a lack of fluids and/or an increase in the concentration of certain osmolites such as salt. If the water volume of the body falls below a certain threshold, or the osmolite concentration becomes too high, the brain signals thirst. The osmolite concentration in the blood is measured with specialized sensors in the hypothalamus, notably in two circumventricular organs that lack an effective blood-brain barrier, the organum vasculosum of the lamina terminalis and the subfornical organ. These areas project to the supraoptic nucleus and paraventricular nucleus, which contain neurons that secrete the antidiuretic hormone, vasopressin, from their nerve endings in the posterior pituitary, but also project to other hypothalamic areas, including especially the median preoptic nucleus to trigger thirst. Continuous dehydration can cause myriad problems, but is most often associated with neurological problems such as seizures, and renal problems. Download high resolution version (1818x2424, 1055 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1818x2424, 1055 KB) Wikipedia does not have an article with this exact name. ... William-Adolphe Bouguereau, self-portrait (1886). ... The suckling of a newborn at its mothers nipple is an example of an instinctive behavior. ... The word drink is primarily a verb, meaning to ingest liquids. ... A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral... In animals the brain, or encephalon (Greek for in the head), is the control center of the central nervous system, responsible for thought. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The hypothalamus (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ... Freeze-fracture morphology of the blood-brain barrier of a rat The blood-brain barrier (abbreviated BBB, not to be confused with the blood-cerebrospinal fluid barrier, a function of the choroid plexus) is a membrane that controls the passage of substances from the blood into the central nervous system. ... The organum vasculosum of the lamina terminalis (OVLT) is one of the circumventricular organs of the brain . ... The Subfornical organ is one of the circumventricular organs of the brain and is involved in thirst-regulation. ... The supraoptic nucleus (SON) is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. ... The paraventricular nucleus (PVN) is an aggregation of neurons in the hypothalamus, adjacent to the third ventricle. ... The posterior pituitary (also called the neurohypophysis) comprises the posterior lobe of the pituitary gland and is part of the endocrine system. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ...


Excessive thirst, known as polydipsia, along with excessive urination, known as polyuria, may be an indication of diabetes. Angiotensin II is a hormone which is a powerful dipsogen (ie it stimulates thirst) which acts via the subfornical organ. Polydipsia is a medical condition in which the patient ingests abnormally large amounts of fluids by mouth. ... Polyuria is the passage of a large volume of urine in a given period. ... This article is about the disease that features high blood sugar. ... Angiotensin is an oligopeptide in the blood that causes vasoconstriction, increased blood pressure, and release of aldosterone from the adrenal cortex. ... A dipsogen is an agent that causes thirst. ...

Contents

Extracellular Thirst

Is the thirst caused by a reduction in the volume of fluid found between cells. This can be caused by a number of things including bleeding, vomiting, diarrhea, sweating, and alcohol consumption.


This type of thirst is also referred to as Volumetric thirst or hypovolemia. Volumetric thirst arises when the volume of blood plasma, i.e. intravascular fluid, decreases.[1] As we lose water, we lose it from all of the fluid compartments in our cells; these being the intracellular, interstitial and intravascular compartments.[1] Pure volumetric thirst is caused by the loss of blood and because sodium is also found in the isotonic solutes that are lost along with blood, the body's need for salt proportionately increases.[1]


Characteristic of all ingestive behavior, hypovolemia or volumetric thirst must be detected, i.e. there must be a mechanism by which to initiate this behavior. This function is accomplished by two sets of receptors; one in the kidneys and the other in the heart.


The kidneys have a specialized set of cells that enable it to recognize changes in blood flow to the kidneys.[1] Naturally, these cells detect the presence of hypovolemia and react accordingly to the loss of blood volume. These cells secrete a hormone called renin when there is a decrease in the flow of blood to the kidneys.[1] Renin flows into the blood and there, initiates the conversion of a protein called angiotensinogen to angiotensin.[1] But in order to exert its effects on the body angiotensin I must be converted by enzymes into its active form, angiotensin II. Physiologically, angiotensin II stimulates the release of hormones by the posterior pituitary gland and the adrenal cortex, causing the kidneys to conserve water and sodium and increase blood pressure by contracting arterial muscles.[1] Behaviorally, angiotensin II causes drinking and a salt appetite.[1] Seemingly, it is this action by the kidneys, to retain both salt and water and constrict blood vessels, that helps to maintain homeostasis by encouraging the animal to both find and ingest salt and water.[1]


The next set of receptors responsible for detecting volumetric thirst are located in the heart; more specifically the atria. Commonly referred to as stretch receptors, these atrial baroreceptors detect the amount of blood that is being pumped back into the heart from the veins.[1] The body constantly returns blood to the heart through veins. Therefore, when the volume of blood being transported back to the heart is decreased, these receptors detect the change in the amount of blood thereby stimulating thirst.[1]


A liquid rich in electrolytes is needed to replenish. An electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. ...

  • Nomadic peoples of the Sahara drink and carry blood as a beverage for their extracellular thirst.

Intracellular Thirst

Thirst triggered when fluid is drawn out if cells due to an increase in the concentration of salts and minerals outside of the cell. Caused by salty snacks etc.


Intracellular thirst is commonly referred to by scholars as osmometric thirst. Osmometric thirst is produced by an increase in the osmotic pressure of the interstitial fluid relative to the intracellular fluid, also known as cellular dehydration.[1] Osmometric thirst also occurs when the tonicity or solute concentration of the interstitial fluid increases.[1] This increase in solute draws water outside of the cell, causing the cell to shrink. Similar to osmosis, osmometric thirst can be correlated with the the movement of water through a semipermeable membrane from an area with a low concentration of solute to an area with a high solute concentration.[1] Neurons that respond to changes in osmotic pressure are known as osmoreceptors.[1] Osmoreceptors are neurons that adjust their firing rate in relation to their level of hydration or lack thereof.[1] Accordingly, as fluid surrounding the cell becomes more concentrated, water flow out of the cell causing it to shrink. The change in the size of the cell causes the osmoreceptors to change their rate of firing, sending signals to different areas of the brain.


As a person eats a salty meal, he or she sustains pure osmometric thirst. Salt is absorbed from the digestive system into the blood plasma causing it to become hypertonic. A hypertonic solution refers to a solution that contains enough solute so that it will draw water out of the cell through the process of osmosis.[1] It is this condition that draws water from the interstitial fluid causing it too to become hypertonic. Because the level of solute is greater outside the cell, water leaves the cell and the cell shrinks, causing a change in the firing of the osmoreceptors thereby initiating osmometric thirst.


Drinking water is best to rid this thirst.


Preventing Subtle Dehydration

For optimal health, experts recommend that humans get 8-10 servings of about 8-ounces (approximately 2 litres) of water per day to maintain hydration. This figure does vary according to ambient temperature, movement and physical size. Being that water is essential to the general function of the human and all animal bodies, eight servings is widely regarded as the minimum for the body to function optimally. However, water can be obtained from many sources, such as foods and other beverages containing water. Getting enough water from your diet and staying hydrated is key to your overall health, including urinary tract and digestive tract health. Impact of a drop of water Water is a chemical substance that is essential to all known forms of life. ... The word drink is primarily a verb, meaning to ingest liquids, see Drinking. ... The urinary system is a system of organs, tubes, muscles, and nerves that work together to create, store, and carry, urine. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and...


When getting your daily water intake, it's important to not rely heavily on caffeinated beverages, as they actually work as a diuretic. Further, moderate or excessive alcohol consumption can lead to dehydration, thus it's important to maintain hydration when drinking caffeinated and alcoholic beverages. A diuretic (colloquially called a water pill) is any drug or herb that elevates the rate of bodily urine excretion (diuresis). ... Functional group of an alcohol molecule. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ...


References

  • M.J. McKinley and A.K. Johnson (2004). "The Physiological Regulation of Thirst and Fluid Intake". News in Physiological Sciences 19 (1): 1-6. Retrieved on 2006-06-02. 

2. For the Manfred Mann album, see 2006 (album). ... June 2 is the 153rd day of the year in the Gregorian calendar (154th in leap years), with 212 days remaining. ...

  1. ^ a b c d e f g h i j k l m n o p q Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.

See also


  Results from FactBites:
 
Thirst - Patient UK (1178 words)
Thirst is thought to be a corrective mechanism which acts as a support to the physiological control of fluid balance in the body.
The intensity of thirst and the amount of water required to quench it is directly proportional to blood osmolality.
In pregnancy, the thirst stimulus is thought to be set at a lower osmolality, which leads to increased intake of water and an increase in circulating blood volume.
  More results at FactBites »

 
 

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