why a person suffering from high blood pressure is advised to take minimum quantity of common salt?

Solute + Solvent  = Solution . All  know that our body contains a number of solute in the form of  fluid . If a persons takes a large no of common salt and who is suffering from high blood pressure, then the ions of salt enters the body fluid with increasing the concentration of the solute in the body which leads to the increase in osmotic pressure which result in the seizing the blood cells and hence salt hold back body fluid which may affect the heart.  And you know that osmotic pressure is directly proportional to the concentration . 
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this may also be point to this that the salt is hydrophillic in nature i.e it attracts water when it is absorbed by our blood it attracts more water to it thus increasing the vol of blood in veins thus increase pressure in circulatory system so bp is increased .. 

this may also a point that salt is hydrophillic in nature i.e it atracts water when it is absorbed by the blood it attracts more water to it thus increasing pressure on circulatory system so bp rises ..

A high quantity of salt in food results in the fluid retention i.e., increase of water content in the body.
When the concentration of salts in the blood increases, the volume of the blood increases due to excessive absorption of water and hence the blood pressure increase in the blood vessels. This results in increased heart rate, to overcome the resistance in the blood vessels. To minimise this extra efforts of heart doctors usually advise high bp patient to take minimum salt.

Osmotic pressure is directly proportional to the concentration of solutes.... Our body fluid contains a number of solutes. On taking large amount of salts, ions enter the body fluid there by raising the conc. of the solutes.... As a result, osmotic pressure increases which may rapture the blood cells and therefore, salt retains body fluid that will make the heart work harder.

eat salt get salt get fat get tension get death
 

Because it can make harmful effects in our internal body system