Osmolality, in Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology is the science of life (from the Greek words bios = life and logos = word). It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and... biology and -1... chemistry, is a measure of The mole (symbol: mol) is one of the seven SI base units and is commonly used in chemistry. It measures the amount of substance of a system and is defined as the amount of substance that contains as many elementary entities as there are atoms in exactly 0.012 kilogram... moles of A substance is soluble in a fluid if it dissolves in the fluid. The dissolved substance is called the solute and the fluid (present in excess) is called the solvent, which together form a solution. The process of dissolving is called solvation, or hydration if the solvent is water. A... solute per kg of water. (Osmolarity is similar but measures moles per litre of solvent.) Osmolality of blood increases with Dehydration is the removal of water (hydor in ancient Greek) from an object. There are many methods of dehydration, with the most common being the application of dry heated air. This causes evaporation of the surface water, which is replaced by water internally. Drying is often used as a method... dehydration and decreases with overhydration.

In normal people, increased osmolality in the blood will stimulate secretion of Antidiuretic hormone (ADH), or arginine vasopressin (AVP), is a peptide hormone produced by the hypothalamus, and stored in the posterior part of the pituitary gland. ADH acts on the kidneys, concentrating the urine by promoting the reabsorption of water from the cortical collecting duct. Physiology Control ADH is activated by... ADH (antidiuretic hormone). This will result in increased water reabsorption, more concentrated urine, and less concentrated plasma. A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma.

Normal osmolality in Blood plasma is a component of blood. It is the liquid in which blood cells are suspended. Blood plasma contains proteins, nutrients, metabolic end products, hormones, and inorganic electrolytes. Serum is the same as blood plasma except that clotting factors (such as fibrin) have been removed. Plasma resembles whey in... blood plasma is about 280 - 296 mosm/kg. This is contributed to mostly by General Name, Symbol, Number sodium, Na, 11 Series alkali metal Group, Period, Block 1 (IA), 3 , s Density, Hardness 968 kg/m3, 0.5 Appearance silvery white Atomic properties Atomic weight 22.989770 amu Atomic radius (calc.) 180 (190) pm Covalent radius 154 pm van der Waals radius 227 pm... sodium, The chloride ion is formed when the element chlorine picks up one electron to form the negatively charged ion Cl−. The salts of hydrochloric acid HCl are also called chlorides. An example is table salt, which is sodium chloride with the formula NaCl. In water, it dissociates into Na... chloride, General Name, Symbol, Number potassium, K, 19 Series alkali metals Group, Period, Block 1(IA), 4 , s Density, Hardness 856 kg/m3, 0.4 Appearance silvery white Atomic properties Atomic weight 39.0983 amu Atomic radius (calc.) 220 (243) pm Covalent radius 196 pm van der Waals radius 275 pm... potassium, Urea Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 and the structure: In some animals, the individual atoms of urea come from carbon dioxide, water, aspartate and ammonia in a metabolic pathway known as the urea cycle, an anabolic process. This expenditure of... urea and A space-filling model of glucose Glucose, a simple monosaccharide sugar, is one of the most important carbohydrates and is used as a source of energy in animals and plants. Glucose is one of the main products of photosynthesis and starts respiration. The natural form (D-glucose) is also referred... glucose, as well as other ions and substances in the blood.

An increase in any osmotically active compound or ion in the blood will cause an increase in the osmolality.

Relationship to molality

Osmolality is molality times number of particles per molecule times another factor.

Units of measurement

SI units: moles per kilogram

The osmole is a non-SI unit, equal to the number of moles of osmotically active particles in an ideal solution. So a mole of glucose equals an osmole of glucose, whereas a mole of sodium chloride equals 2 osmoles and a mole of calcium dichloride equals 3 osmoles due to dissociation.

Measurement of osmolality

Osmolality can be measured with an osmometer by determining the fall in freezing point when compared to deionised water (which has an osmolality of 0 mosm/L). It can also be estimated from levels of specific solutes measured in the blood.

If there is a difference between the measured and estimated osmolalities, this may be because of another osmotically-active substance that was not accounted for.