 Dear students, in this topic we shall discuss the blood pressure. You know that contractions of the ventricles of heart generate blood pressure. This pressure causes the blood to flow in the arteries away from the heart, from the areas of high pressure to the areas of lower pressure. Dear students, the blood pressure generated from the ventricles changes during survival during circulation through different regions of the body. Pressure is highest in the aorta. It decreases during circulation through arterioles and capillaries. The narrow diameter vessels offer substantial resistance to flow. This is why blood pressure decreases in the less diameter vessels. So that when the blood enters the ventricle, the pressure of the blood is almost finished. This is why there is no pressure in the ventricle. Similarly, during the cardiac cycle, the blood pressure changes. Arterial blood pressure is highest during the ventricular systole. This pressure is known as systolic blood pressure. Due to this pressure, the walls of the arteries stretch. Pressure drops when the ventricle relaxes. That is during diastole. This diastolic pressure is comparatively lower. And this lower diastolic pressure is maintained in the arteries. This pressure, which is diastole of the ventricle of heart, although it is not pumping, still some pressure is maintained. It is because of the contraction of the elastic walls of arteries. Dear students, now we shall discuss the regulation of blood pressure. Blood pressure fluctuates due to the contraction or relaxation of smooth muscles of the arterial walls. In the walls of arterials, contractions and relaxations of smooth muscle cause either vasodilation or vasoconstriction. Vasoconstriction causes the arterioles to become narrow. And this causes blood pressure to increase. Whereas vasodilation increases the diameter of arterioles as a result, blood pressure falls. The contraction of smooth muscles of arterial walls is regulated through chemical, nervous and hormonal controls. These controls are affected by physical or emotional states. For example, exercise and stress. The hormones raised during stress also cause vasodilation or vasoconstriction. So they regulate blood pressure. These hormones include cortisol, epinephrine and norepinephrine. In addition, renin and eutensin, the aldosterone system of kidneys which regulates blood volume also affects the blood pressure. In addition, nitric oxide serves as a major inducer of vasodilation in the circulatory system. And an endothelene is a potent inducer of vasoconstriction and thus helps to regulate blood pressure.