Sodium in extracellular fluid

Sodium chloride is primarily restricted to the extracellular space. When sodium is ingested without water the excess sodium will remain in the extracellular space, where it will raise the plasma sodium concentration and the plasma osmolality.

The increase in osmolality will result in the osmotic movement of water out of the cells into the extracellular space until the osmolality is the same in two compartments.

As a result, the glomerular filtration rate increases, and the excess sodium and water are excreted by the kidney to restore the normal extracellular volume.

A low sodium diet leads to a transient negative sodium balance, thereby reducing extracellular volume, a process that activates the sodium-conserving mechanisms of the kidney.

Because sodium is the major extracellular cation, shifts in serum sodium levels are usually inversely correlated with the hydration state of the extracellular fluid compartment.

The pathophysiology of hyponatremia then is usually expansion of body fluids leading to excess total body water. Symptomatic hyponatremia usually does not occur until the serum is below 120 to 125 mEq/L.

In the normal individual, the kidney behaves as though extracellular volume was the regulatory stimulus articulating renal excretion with salt intake.

Extra note:
Osmotic pressure is measured in milliosmoles. When the number of particles is measured per kilogram of solvent, the correct term s osmolality, when measured per liter of solvent, the correct term is osmolarity.
Sodium in extracellular fluid

Magnesium Function in Human Body

Magnesium Function in Human Body
Of the total magnesium, about 0.5 gm/kg fat-free tissue, roughly 60% is located in bone. The function of magnesium in hard tissues is not known; one third of it is in combination with phosphate, and the remainder appears to be adsorbed loosely on the surface of the mineral structure.

A small amount of magnesium is dissolved in the extracellular fluid and is easily exchanged with that adsorbed at the bone surface. Only 1 – 3 mg/100ml is present in serum; of this about 35% is bound to protein or complexed with other substances and is not available for exchange.

Within the cells of soft tissue the concentration of magnesium is greater than any other mineral except potassium. Loss of magnesium from the body therefore is usually associated with tissue breakdown and cell destruction.

Magnesium is required for cellular respiration, specifically in oxidative phosphorylation leading to formation of ATP. In fact magnesium is necessary for all phosphate transferring system and in certain tissues, such a heart, a major fraction of the Magnesium present is complexed with ATP, ADP and AMP.

Chronic deficiency produces alopecia, skin lesions and swollen gums. High calcium intakes tend to aggravate symptoms of magnesium deficiency. Personality changes, muscles tremor, lack of coordination and gastrointestinal disturbances developed after three months on the deficient diet. In addition, serum calcium and potassium decreased as serum magnesium decreased and rose to normal if magnesium therapy instituted.

Magnesium deficiency does not appear to be a problem in most human dietaries since the mineral element is widely distributed in foodstuffs.

In a normal adequate diet about 30% of the total magnesium intake may come from green vegetables that contain magnesium porphyrin, chlorophyll.
Magnesium Function in Human Body