SamaraLauren Boyd

The Thirst Mechanism

*The ImportanceWater is important for maintaining body fluid homeostasis.Fluid Homeostasis is necessary for1) normal reactions within the cells2) Maintenance by adaptation to changes in water intake

and water loss3) Water balanceThe amount of water that is consumed and is produced by the body via food, beverages, and metabolism is the amount that is excreted through the kidneys, skin, lungs, and feces.Body water is contained in either Intracellular fluid compartments (majority of body water), Extracellular fluid compartments, Interstitial and Intravascular.

Thirst is often the first sign of dehydration

*The Thirst Mechanism is controlled in the hypothalamus*The hypothalamus

detects changes and stimulates release of anti-diuretic hormone:*ADH signals kidneys to

reduce urine flow and retrun more water to the bloodstream.*Kidney releases

angiotension II (stimulated by secretion of renin) which constricts the blood vessels and causes retention of water*Water is also drawn out

of salivary glands in mouth to cause dryness

*Thirst Mechanism *• The thirst mechanism is the primary regulator of water intake

and involves hormonal and neural input as well as voluntary behaviors. *• Stimulation of the thirst center in the hypothalamus gives you

the desire to drink.

*• There are three major reasons why dehydration leads to thirst: *1. When saliva production decreases, the mouth and throat

become dry. Impulses go from the dry mouth and throat to the thirst center in the hypothalamus, stimulating that area. *2. When you are dehydrated, blood osmotic pressure increases,

stimulating osmoreceptors in the hypothalamus and the thirst center in the hypothalamus is now further activated. *3. Decreased blood volume causes a decrease in blood pressure

that is signaled by baroreceptors and stimulates the release of renin from the kidney. This causes the production of angiotensin II which stimulates the thirst center in the hypothalamus.