Osmoreceptors: Your Body’s Dehydration Defenders
July 23, 2019
By Karen Wilkinson, RN, NHA, CLNC – CareerSmart® Learning Contributor
The “Dog Days” of summer technically arrived on July 3 with the dawn rising of Sirius, the Dog Star. But we don’t have to look to the skies to know that these hot, sultry days have shown up. We know they are here when we long for an air-conditioned place to cool off and a beverage to quench our thirst.
Have you thought about the reason you voluntarily reach for something to drink? Adult human bodies are comprised of up to 60% water. According to H.H. Mitchell in the Journal of Biological Chemistry 158, our lungs are about 83% water, muscles and kidneys are 79%, brain and heart are 73%, skin is 64%, and bones are 31%. With water making up so much of our bodies, it is necessary to support several essential functions. First and foremost, the body depends on water to survive as a vital nutrient for cell life. Water also regulates body temperature through sweating and respiration, helps transport carbohydrates and proteins in the bloodstream, flushes waste through urination, lubricates joints, absorbs shock for the brain, spinal cord, and fetus, and forms saliva.
Thirst is one of our body’s regulators that results from a deficit of water in our bodies and the physiological triggers that result. Our first line of “dehydration” defense rests with osmoreceptors located primarily in the hypothalamus of the brain, but also in the oropharynx, gastrointestinal tract, and the liver-portal system. These osmoreceptors trigger thirst by responding to dehydration at a cellular level caused by minor changes in osmolality as fluid leaves the cells through osmosis. Volume receptors are also present that kick in and respond to more drastic fluid losses as they affect vascular and interstitial spaces, such as hemorrhage or severe dehydration. But satisfying thirst also has perceptual components. Our preferences and other cultural factors related to flavor, color, odor, and temperature of beverages affect our choices. For example, iced tea or cold water may be more appealing than a hot beverage on a hot day for most of us. But others may prefer room temperature water over cold water, or a particular flavored or sweetened beverage rather than an unsweetened one.
So how much fluid is enough for a healthy adult? The Institute of Medicine of the National Academies has determined that normal hydration is possible over a wide range of daily intake which includes water, other beverages, and food. While water in food provides about 19% of the daily total, recommendations for total daily fluid intake for adult males and females are 3.7 liters and 2.7 liters per day, respectively, or about 15 ½ cups for adult men and 11 ½ cups for adult women.
During the “Dog Days” of summer, give a nod to the marvels of your body’s osmoreceptor alert system and drink up. And don’t forget your furry friends. They need plenty of fresh water to drink during these hot days, too.
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1The Old Farmer’s Almanac. (June 26, 2019). The Dog Days of Summer. Retrieved July 22, 2019 from https://www.almanac.com/content/what-are-dog-days-summer
2,3USGS Water Science School. The Water in You: Water and the Human Body. Retrieved July 22, 2019 from https://www.usgs.gov/special-topic/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects
4 Institute of Medicine of the National Academies. (2005). Chapter 4: Water. In Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, pp. 102-105. Washington, D.C.: The National Academies Press.