Blood is an extremely important fluid that is needed everywhere in the body; it is required for transporting oxygen to different areas of the body, bringing carbon dioxide to the lungs for removal, regulating body temperature, and delivering immune cells to the site of an injury. The heart pumps blood out to the organs and tissues, and this pumping is your blood pressure. Your blood pressure must be maintained at normal levels; if it is too high (known as hypertension), it can put strain on your arteries and heart, and lead to a heart attack or stroke; if it is too low (known as hypotension), it can result in not enough blood reaching vital organs, and lead to fainting, stroke or kidney failure.
Blood pressure is measured in units of millimeters of mercury (mmHg) and a blood pressure reading will note your systolic and diastolic blood pressure. Systolic blood pressure (the top number in a reading) specifies the pressure that your blood exerts against the walls of your arteries when the heart beats. Diastolic blood pressure (the bottom number in a reading) specifies the pressure that your blood exerts against the walls of your arteries when the heart is resting.