Systolic and diastolic blood pressure are effects of blood being pumped through your body. Find out what they are:
The heart consists of two large chambers - the ventricles - and two smaller chambers - the atria. The ventricles collect blood from the atria and expel it towards the peripheral beds of blood vessels within the body and the lungs. The atria collect blood from these peripheral beds and prime the ventricles.
When the ventricles (the two large chambers inside the heart) contract and pump blood out of the heart, the blood pressure reaches its maximum value in the cycle: Systolic pressure.
When the ventricles relax and are filled again with blood, the blood pressure reaches its minimum value in the cycle: Diastolic pressure.