WHY PEOPLE WITH HIGH BLOOD PRESSURE CAN'T EAT SALTY FOOD??

When i was child i ever heard that person with high blood pressure is forbidden to eat salty food. my mom also gets high blood pressure, so almost everyday i eat tasteless food in home. i never ask to my mom. i just speculated that salt consist some poison so we can't eat it to much, and i never search what is the right answer. 
now in college i get the answer. this case can be explain by osmotic pressure.
it's not about a poisonous matter, because we also need salt. salt consists yodium which is also needed to our body. it's because salt make solution in our body more concentrated, so that, it makes more liquid (solution) enter blood vessel through the blood vessel wall. this thing make heart work harder because it must push blood with high concentration of water. if this happen continously, it may break the blood vessel.
for more understanding, look at this picture:

the violet cylinder is a blood vessel. the outside of blood vessel (blue color) is body liquid. of course it's not just a liquid. it is solution with many ion or something there, but people usually call it liquid. this solution also consist of Na⁺ ion, with come from salt, NaCl.
blood vessel wall is semipermeable, so that water can enter the blood vessel through it's wall. when the concentration of the solution is higher, it make osmotic pressure, the pressure which is push water to enter blood vessel, become higher too. as a consequence, the blood pressure, as a ward force of the osmotic pressure also become higher, which is mean that heart have to push blood with stronger force. when the blood vessel consists much water, and when it can't endure water's osmotic pressure, the blood vessel will be broken.
thus, if you have high blood pressure, you have to avoid salty food, because it can break your blood vessel.

thanks for Prof. Drs. H. Suhadi Ibnu, M.A, Ph.D, yesterday was nice lecture :)