Question

You go for a run on a really hot day, which makes you sweat more than usual. What is happening to the water balance in your body? Include: the difference between intracellular and extracellular fluid compartment. The movement of the fluids and water between the compartments. What role sodium plays in water balance, how is the sodium regulated and how it aids in the bodys homeostatic equilibrium.How is the bodys response to the disruption in watwr balance and how is it compensated for?

Answer 1

Camparmental changes & movement:

Dehydration is a general state in which there is a total-body fluid deficit. Under normal physiologic conditions, water constitutes 70% of lean body mass. In infants, the proportion is approximately 75%. Two thirds of the fluid is intracellular, and one third is extracellular. Of the extracellular fluid, 75% is interstitial and 25% is intravascular. Fluid that is lost from the body often has an electrolyte composition similar to that of plasma. Most of the fluid deficit during the early stages of dehydration is from the extracellular space, but over time, the fluid losses equilibrate, and fluid leaves the intracellular space. During the recovery phase, fluid administered to the patient is located in the extracellular space and needs time to equilibrate with the intracellular space.

Sodium & Homeostasis :

Salt is composed of Sodium Chloride (NaCl) which in body water becomes essential electrolytes, viz., Sodium (Na⁺) and Chloride (Cl⁻) ions, including in the blood and other extracellular fluids (ECF). Na⁺ ions are necessary cations in muscle contractions and their depletion will effect all the muscles in body including smooth muscle contraction of blood vessels, a fact which is utilized in lowering the blood pressure. Na⁺ ions also hold water with them in the ECF. Na⁺ homeostasis in body is maintained by thirst (water intake), kidneys (urinary excretion) and skin (sweating). In Na⁺ withdrawal, body tries to maintain homeostasis as far as possible. However, in certain conditions (e.g., during exercise, intake of drugs and in disorders causing Syndrome of Inappropriate Anti Diuretic Hormone Secretion (SIADH), diuretics, diarrhea) coupled with moderate or severe dietary salt restriction (anorexia nervosa), hyponatremia can get precipitated. Hyponatremia is one end point in the spectrum of disorders caused by severe Na⁺ depletion whereas in moderate depletion it can cause hypohydration (or less total body water) and lower urinary volume (U v ). Moreover, salt sensitivity varies in various populations leading to different responses in relation to dietary Na⁺ intake. Diabetes and Hypertension often co-exist but Na⁺ withdrawal in salt sensitive subjects worsens diabetes though hypertension gets better and reverse occurs in salt loading. Therefore, Na⁺ or salt restriction may be non-physiological. In hypertensive subjects other alternatives to Na⁺ withdrawal could be Potassium (K⁺) and Calcium (Ca⁺²) supplementation. Further studies are required to monitor safety/side effects of salt restriction.

Sodium role in homeostasis-

Na⁺ homeostasis in body is maintained by thirst (water intake), kidneys (urinary excretion) and skin (sweating). In Na⁺ withdrawal, body tries to maintain homeostasis as far as possible

Body response:

The body's initial responses to dehydration are thirst to increase water intake, and decreased urine output to try to conserve water loss. The urine will become concentrated and more yellow in color. As the level of water loss increases, more symptoms can become apparent.