Plasma osmolality - What is Plasma osmolality?

In addition to influencing the rate of water excretion, ADH plays a central role in osmoregulation because its release is directly affected by the plasma osmolality. At a plasma osmolality of less than 275 mosm/kg, which usually represents a plasma Na + concentration of less than 135-137 mmol/L, there is essentially no circulating ADH. As the plasma osmolality rises above this threshold, however, the secretion of ADH increases progressively.

Two simple examples will illustrate the basic mechanisms of osmoregulation, which is so efficient that the plasma Na + concentration is normally maintained within 1-2% of its baseline value.

Ingestion of a water load leads to an initial reduction in the plasma osmolality, thereby diminishing the release of ADH. The ensuing reduction in water reabsorption in the collecting tubules allows the excess water to be excreted in a dilute urine.

Water loss resulting from sweating is followed by, in sequence, a rise in both plasma osmolality and ADH secretion, enhanced water reabsorption, and the appropriate excretion of a small volume of concentrated urine. This renal effect of ADH minimizes further water loss but does not replace the existing water deficit. Thus, optimal osmoregulation requires an increase in water intake, which is mediated by a concurrent stimulation of thirst. The importance of thirst can also be illustrated by studies in patients with central diabetes insipidus, who are deficient in ADH. These patients often complain of marked polyuria, which is caused by the decline in water reabsorption in the collecting tubules. However, they do not typically become hypernatraemic, because urinary water loss is offset by the thirst mechanism.

Also see Osmotic pressure, Plasma osmolality


Share |

Related Articles on Nutrition
Recurrent Gallstones
Vitamin and Mineral Supplements: Use With Care
Dietary requirements
Nutrition and Ageing
Water and electrolyte balance
Food allergy and food intolerance
Protein-energy malnutrition
Energy Expenditure
Basal Metabolic Rate
Recommended healthy diet
Energy Stores
Osmotic pressure
Plasma osmolality
Illness and Diet
When to eat what?
Take a cold bath
Rules for health protection
Characteristics of good health
Diet during Winter Alteril
Vitamin Cottage
Arbonne Vitamins
B12 Solgar Vitamin
Benefits of Resveratrol
Does Hydroxycut Work
Kombucha Danger
Hydroxycut Medical Side Effects
Miracle Mineral Supplement
Solgar Vitamin D 1000 IU
Sources of Vitamin D
Swanson Vitamins
What is a Good Vitamin for My Teenager to Take?
Two Main Vitamins in Sweet Potatoes
Vitamins for COPD
Using Kefir to Treat Candida Yeast
Vitamin B12 Cereals
Vitamin K Cream
Vitamin Shoppe
Vitamin Water
Vitamin World

Nutrition - Vitamins | Amino Acids | Herbs | Minerals | Nutrients | Supplements | Enzymes
Wellness - Healthy Living | Dental Care | Products | Skin Vitamins | Ayurveda | Slideshow
Health - Deficiency | Alternative Medicines | How To | Symptoms | Food Kitchen How tos?
Fitness - Exercises | Gardening
Food & Cooking - Recipes | Fruits & Vegetables
Healthy Eating & Diet - Diet | Weight Loss | Green Tea | Noni Juice | Acai
Online Vitamins Guide

Nutrition Articles | Your Feedback & Suggestions | Newsletter
Disclaimer | Blog
Home © 2001-2013 All rights reserved.