Hypertension occurs when the heart forcibly pumps the blood, or when the arterioles become narrower than the normal size.
This narrowing might have caused by several diseases as a renal or adrenal disease, but since the percent of the patients that have hypertension because of this disease is very low (2%-5%), there is no certain cause tell now. However, hypertension could be a temporary change in the body to regulate body internal environment (homeostasis). This normal change could be due to the need for extra blood and blood nutrients. For example, while doing strenuous exercises like running and weight lifting, the heart beats is rapidly increasing which lead to temporal hypertension that is reduced by finishing these efforts. Moreover, the nervous and endocrine system regulates blood pressure by several processes. In the nervous system, the series of neurons that are conducted with the brain, make the brain in contact with the blood vessels and heart muscles, that when there is any change in the body, the brain could determine whether the body needs increasing or decreasing the blood pressure.
After that brain controls the contraction of the heart and blood vessels by electrochemical impulses from the autonomic nervous system; so when the heart contracts rapidly or when the blood vessels become narrower because of nerve stimulation, the blood pressure increase (hypertension). In the endocrine system, there is a lot of hormones that control the increase in blood pressure. For instance, hormones such as insulin, and the renin-angiotensin system play a key role in changing the concentration of the plasma of the blood, which affect the blood pressure (i.e. increasing the concentration of the blood increase the blood pressure). Anywise, the normal pressure is changing during the day as a result for stress and fatigue, the thing that leads doctors to have many readings of the patient’s pressure before determining whether they have hypertension or not.