When the salt content of blood goes up, it attracts water from around cells into the blood to dilute it, otherwise the blood would be too salty. There is salt as sodium outside every cell in the body. When the salt content of the fluid around your cells goes up, it attracts water from the blood and swelling occurs. Our kidneys are responsible for regulating salt and water levels in the body. When salt and water levels increase around cells, the excess is drawn into your blood, which is filtered by the kidneys. When the kidneys don't function correctly, fluid builds up around cells and in the blood. If there is more fluid in the blood, the heart has to work harder and blood pressure can go up because there is more pressure on the walls of the blood vessels. The heart can get weaker or worn out from the extra work.
Obesity is strongly associated with having high blood pressure so it is very important to maintain a healthy weight. A weight increase of 10kg is associated with an increase in systolic blood pressure of 2-3mmHg. People who are overweight are 2 to 6 times more likely to develop hypertension. Also being obese may lower certain actions of insulin that open blood vessels and it may cause structural changes in the kidney and abnormal handling of sodium. It is also associated with alterations in the systems that regulate blood flow.
Genetic factors are thought to play a prominent role in the development of high blood pressure. Unfortunately, the genes for high blood pressure have not yet been identified. The current research in this area is focused on the genetic factors that affect the renin-angiotensin-aldosterone system. This system helps to regulate blood pressure by controlling salt balance and the tone - state of elasticity - of the arteries. Chromosomes 13 and 18 are responsible for housing the genes responsible for blood pressure regulation, although pinning down the range of specific genes involved in high blood pressure is more difficult.
