Factors which regulate body water

Sodium is by far the major solute in extracellular fluids, so it effectively determines the osmolarity of extracellular fluids. An important concept is that regulation of osmolarity must be integrated with regulation of volume, because changes in water volume alone have diluting or concentrating effects on the bodily fluids.

For example, when you become dehydrated you lose proportionately more water than solute sodium , so the osmolarity of your bodily fluids increases. In this situation the body must conserve water but not sodium, thus stemming the rise in osmolarity.

If you lose a large amount of blood from trauma or surgery, however, your loses of sodium and water are proportionate to the composition of bodily fluids.

In this situation the body should conserve both water and sodium. As noted above, ADH plays a role in lowering osmolarity reducing sodium concentration by increasing water reabsorption in the kidneys, thus helping to dilute bodily fluids.

To prevent osmolarity from decreasing below normal, the kidneys also have a regulated mechanism for reabsorbing sodium in the distal nephron. This mechanism is controlled by aldosterone, a steroid hormone produced by the adrenal cortex.

Aldosterone secretion is controlled two ways:. The adrenal cortex directly senses plasma osmolarity. When the osmolarity increases above normal, aldosterone secretion is inhibited. The lack of aldosterone causes less sodium to be reabsorbed in the distal tubule.

Remember that in this setting ADH secretion will increase to conserve water, thus complementing the effect of low aldosterone levels to decrease the osmolarity of bodily fluids.

Physical trainers recommend pre-hydrating before a workout, which will make up for any fluid loss from sweating. According to fitness trainers at ISSA , a general rule is to drink about two cups 30 minutes before working out and then one cup of water or sports drink every 15 minutes during your workout. You can also calculate how much water you should drink per day by your weight. The amount of water a person needs depends on weight — the more someone weighs, the more they need to drink.

You should adjust this number based on how much you are exercising, especially since you lose significant fluids through sweat. A sensible guideline is to add 12 oz of water to your daily total intake for every 30 minutes that you exercise. For example, if you work out for 45 minutes a day, you would add 18 oz of water to your daily amount.

And as aforementioned, climate and temperature will also require additional water intake on top of your regular amount. Keep track of your water intake with a specific container such as a reusable water bottle.

Depending on your needs, you can set a goal for how many times you need to finish the container in a day. As you can see, there are many intricate and complicated processes that must happen within the body in order to maintain a balanced amount of water. With this in mind, you can easily stay healthy and hydrated when you're mindful of your water intake on all your daily adventures.

Water Loss What about other factors affecting water intake? Calculate Your Sweat Rate To find out exactly how much additional water you need to drink, you can calculate your sweat rate by taking your pre-exercise body weight and subtracting it from your exercise post-exercise body weight. Water loss from the body occurs predominantly through the renal system. A person produces an average of 1. Although the volume of urine varies in response to hydration levels, there is a minimum volume of urine production required for proper bodily functions.

The kidney excretes to milliosmoles of solutes per day to rid the body of a variety of excess salts and other water-soluble chemical wastes, most notably creatinine, urea, and uric acid. Failure to produce the minimum volume of urine means that metabolic wastes cannot be effectively removed from the body, a situation that can impair organ function. The minimum level of urine production necessary to maintain normal function is about 0. The kidneys also must make adjustments in the event of ingestion of too much fluid.

Diuresis , which is the production of urine in excess of normal levels, begins about 30 minutes after drinking a large quantity of fluid. Diuresis reaches a peak after about 1 hour, and normal urine production is reestablished after about 3 hours. Antidiuretic hormone ADH , also known as vasopressin, controls the amount of water reabsorbed from the collecting ducts and tubules in the kidney. This hormone is produced in the hypothalamus and is delivered to the posterior pituitary for storage and release Figure When the osmoreceptors in the hypothalamus detect an increase in the concentration of blood plasma, the hypothalamus signals the release of ADH from the posterior pituitary into the blood.

ADH has two major effects. It constricts the arterioles in the peripheral circulation, which reduces the flow of blood to the extremities and thereby increases the blood supply to the core of the body. ADH also causes the epithelial cells that line the renal collecting tubules to move water channel proteins, called aquaporins, from the interior of the cells to the apical surface, where these proteins are inserted into the cell membrane Figure The result is an increase in the water permeability of these cells and, thus, a large increase in water passage from the urine through the walls of the collecting tubules, leading to more reabsorption of water into the bloodstream.

When the blood plasma becomes less concentrated and the level of ADH decreases, aquaporins are removed from collecting tubule cell membranes, and the passage of water out of urine and into the blood decreases. A diuretic is a compound that increases urine output and therefore decreases water conservation by the body.

Diuretics are used to treat hypertension, congestive heart failure, and fluid retention associated with menstruation. Alcohol acts as a diuretic by inhibiting the release of ADH. Additionally, caffeine, when consumed in high concentrations, acts as a diuretic. Homeostasis requires that water intake and output be balanced.