Regulation of Water Intake (Nursing)

00:01 So to maintain homeostasis in the body, water intake must equal water output.

00:09 We use about 2500 milliliters of water a day.

00:14 Most of our water it's going to be taken in by way of the foods that we ingest, the beverages that we drink, and also by a small amount of metabolism that happens in our body cells.

00:28 Metabolic water, also sometimes referred to as the water of oxidation, is going to be water that is produced by the chemical reactions that occur during cellular metabolism.

00:41 Water output is going to mostly be in the form of urine.

00:45 But we also get rid of water in a way such as insensible water loss, which is water loss that we do not perceive, and also perspiration, and our feces.

00:59 The osmolality in our body is usually maintained around 280 to 300 mOsm.

01:07 If, however, there is a rise in our bodies osmolality, this will stimulate the thirst centers in our brain to stimulate thirst so that we ingest more water.

01:20 It also can cause a release of antidiuretic hormone.

01:26 Antidiuretic hormone will lead to more reabsorption of water in our kidneys.

01:33 If our body's osmolality decreases, this will cause inhibition of the thirst centers in the brain.

01:41 Also, we will inhibit our antidiuretic hormone which will allow the production of a dilute urine and release or get rid of some of the extra water found in our bodies fluids.

01:56 So in a day, if we just look at where our water intake comes from and where our water output goes from, we find that in a day, we're going to mostly bring in our fluids by way of the beverages that we drink.

02:12 We also bring in about 30% of our fluids from foods.

02:17 And the remaining 10% of the water that we bring in, in a day is going to come from metabolic reactions occurring in our body cells.

02:26 When it comes to water output, we find that the majority of the water leaves our body by way of urine.

02:34 Also, about 28% of our water is going to leave in the form of insensible water loss, which is basically imperceptible sweating or loss of fluids where we don't actually notice it.

02:48 The remaining is going to be from our sweat as well as our feces.

02:55 So when it comes to the thirst mechanism, this is going to be the driving force for our water intake.

03:03 This is governed by the hypothalamic thirst centers in the hypothalamus.

03:08 Where hypothalamic osmoreceptors are going to detect the extracellular fluids osmolality, and then be activated if there is an increased plasma osmolality of as small as just 1% or 2%.

03:25 It will also be activated if we start to have a dry mouth.

03:31 Also a decreased blood volume or blood pressure and also the activation of angiotensin II or baroreceptors.

03:42 Drinking water is then going to inhibit the thirst center.

03:49 The inhibitory feedback signal is going to include things like the relief of our dry mouth, as well as activation of stomach and intestinal stretch receptors as the water goes through our digestive tract.

04:05 So putting this all together, an increase in our extracellular fluids osmolality, or a decrease in our plasma volumes are going to cause the activation of our hypothalamic thirst centers by either responding to osmoreceptors in the hypothalamus, or responding to a dry mouth, or responding to an increase in the presence of angiotensin II.

04:37 Once stimulated, the hypothalamic thirst center will cause a sensation of thirst making a person decide to drink, which will lead to the moistening of the mouth, and the throat, as well as the stretch of the stomach and intestines as the water goes through the GI tract.

04:57 Also, the water will be absorbed from the GI tract and this will lead to a decrease in our extracellular osmolality as we start to absorb more water and decrease the concentration.

05:11 Also, because we're absorbing more water, we're going to increase the volume of our plasma.

05:19 The relief of dry mouth and the stretch receptors in our stomach and intestines are also going to send inhibitory signals back to the hypothalamic center in a negative feedback loop.