Salt is vital for proper functioning of nervous system, without salt electrolyte balance of blood will be impacted, and you might go unconscious if enough salt is not provided to your body. However excess of salt needs to be filtered out by your kidney in form of urine. So if you increase your salt intake , your kidney will be overloaded, this slows down water filtering from the blood, hence blood pressure will increase.
The unwanted fluid of your blood is filtered and removed by kidney in the form of urine. To do this your kidney use osmosis process to remove extra water out of your blood. This osmosis process use a balance of sodium and potassium to pull the water from the bloodstream into a collecting channel that is bladder.So when we increase the amount of salt in our diet, the amount of sodium increases in your bloodstream and breaks the delicate balance of sodium and potassium, it reduces the ability of kidney to remove water. This extra fluid and strain on the delicate blood vessels ,result high blood pressure.
Prolonged high intake of salt , will overload kidney and might damage your kidney. Once the blood pressure raised due to too much salt intake may damage the arteries, leading to the brain and heart and causes a slight reduction in the amount of blood reaching to the heart and brain. In this condition heart and brain don't work as well as they should, because they are not receiving enough oxygen and nutrients. If this happen over the time the part of your brain and heart that was not receiving blood from longer time ,it dies and results heart attack.
On the other hand in low blood pressure may help to reduce some of the problems.