<Tr> <Th> MeSH </Th> <Td> D001795 </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Blood pressure (BP) is the pressure of circulating blood on the walls of blood vessels . When used without further specification, "blood pressure" usually refers to the pressure in large arteries of the systemic circulation . Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heart beat) over diastolic pressure (minimum in between two heart beats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure (considered to be zero for convenience). </P> <P> It is one of the vital signs, along with respiratory rate, heart rate, oxygen saturation, and body temperature . Normal resting blood pressure in an adult is approximately 120 millimetres of mercury (16 kPa) systolic, and 80 millimetres of mercury (11 kPa) diastolic, abbreviated "120 / 80 mmHg". </P>

What are the two parts of blood pressure