Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes High Blood Pressure ?
    ### Response:
    Changes in Body Functions Researchers continue to study how various changes in normal body functions cause high blood pressure. The key functions affected in high blood pressure include -  kidney fluid and salt balances  -  the renin-angiotensin-aldosterone system   - the sympathetic nervous system activity   - blood vessel structure and function.
    