Blood pressure : The force which the blood applies against the walls of blood vessels is known as blood pressure.

The pressure of the blood in the circulatory system depends upon :

1. Changes of the circulatory space due to contraction and relaxation of heart and blood vessels.

2. The amount of blood entering and leaving the blood vessels.

3. Total blood volume.

4. The viscosity of blood.

5. The elasticity of the blood vessels.

Systolic pressure : It is the pressure of blood during systolic phase. It is maximum and is responsible for the movement of blood in the arteries. Normal systolic pressure is 120—130 mm of Hg.

Diastolic pressure : It is the blood pressure during diastolic phase of heart when blood is received in the heart. Normal diastolic pressure is 80 mm of Hg. 

The blood pressure is measured by the instrument called sphygnomanometer.