<prompt> The majority of body sodium is present ?Extra cellular fluidIntra cellular fluidPlasmaBone  <response>: D i.e. Bone- Typical western diet consumption provides approximately 150 mmol of sodium chloride NaC1 dailyQ.- Normal level of serum sodium is 136 -145 mmolL SI unit or 136- 145 megL conventional unitQ.Na - I ATP pase pump actively transpos Na out of cells. As a result, 85- 90 of all sodium is extracellularQ and ECF volume is a reflection of total body Na content2. And in the same way total body Na content is a reflection of ECF volume.Sodium reserve is chiefly stored in stomach wallQ, which makes it alkaline to counter balance the acidic environment. 30-40 sodium is stored in skeletal muscles.- The normal plasma osmolality is 275 - 290 milliosmoleskg. To maintain it, normally about 600 mosmolsday solute must be excreted. And since maximum urine osmolality is 1200 mosmolskg a minimum urine out put of 500 mL d is required.- Osmoreceptor located in anterolateral hypothalmusQ is stimulated by hypeonicity. Ineffective osmols i.e. solutes that do not contribute to shift water across cell membrane, like urea and glucoseQ do not play a role in stimulating thirst. The average osmotic threshold for thirst is - 295 mosmolkg. Osmotic adaptation is a defence mechanism of brain cells in chronic hypo hyper natremia against large water shiftsQ. It is mediated by initialshifts of K Na fb synthesis, impo or expo of organic solutes osmolytes such as inositol, betaine glutamineQ. In chronic hyponatremia brain cells lose in chronic hypernatremia gain solutes. Sodium is the principal cation content of ECF. The total body sodium is - 5000 mmol, of which 44 is in extracellular fluid 9 is in intracellular fluid and remaining 47 is in boneQ.98 of potassium K is intracellular 2 in extracellular fluid. 34 of total boy IC - 3500 minol is found in skeletal muclesQ. Normal adult ingests - 1.0 rnmolkg of IC in food. Fruit, milk honey are rich in K. 