The primary determinant of maintenance water requirement appears to be metabolic (Holliday and Segar, 1957), but the actual estimation of water requirement is highly variable and quite complex. This can become life threatening when more than 10% of body weight is lost.
If the sensation of thirst is not met by water consumption, or if the thirst mechanism is inoperative because of intense, sustained exertion, especially at a high altitude (Buskirk and Mendez, 1967), dehydration will eventually result. Despite the kidney's ability to compensate, its limitations require the effective use of the thirst sensation to maintain water balance. Normally functioning kidneys can adjust urine osmolarity from 40 to 1,400 mosmol/liter, depending both on water intake and on dietary solute load. Because the kidney must excrete waste products, the solute load-composed of the nitrogen-containing breakdown products of protein metabolism (principally urea), sulfates, phosphates, and other electrolytes-determines the minimal volume of water required for urine formation. Ox is water of oxidation.įigure 11-1 includes an estimate of minimal urine volume required when urinary solute concentration is maximal (about 1,400 mosmol/ liter in the healthy adult and 700 mosmol/liter in the infant). M is minimal urine volume at maximal solute concentration. Routes and approximate magnitude of water intake and outgo without sweating. Diarrhea can increase intestinal loss dramatically.
#Perfect balance electrolyte skin
Exertion under any of these conditions can cause up to a 10-fold increase in water loss from skin and lungs. These insensible losses can all be increased under certain conditions, including high temperatures, high altitude, and dry air. As Figure 11-1 shows, even in the absence of visible perspiration, approximately one-half of the turnover occurs through what is called insensible water loss, i.e., water lost from the lungs and skin.
The normal daily turnover of water via these routes is approximately 4% of total body weight in adults and much higher, 15% of total body weight, in infants. Accordingly, body water, as a percentage of body mass, is higher in men than in women and tends to fall with age in both.įigure 11-1 shows the routes and approximate magnitudes of water intake and loss in an environment cool enough to prevent sweating. Water is the most abundant constituent of the human body, accounting for one-half to four-fifths of body weight, depending mainly on body fat content.
0 kommentar(er)
