 Dear students, in this topic we shall discuss the relationship between the pressure and flow of blood. The difference in blood pressure between two points in a flow path gives rise to a pressure gradient. This pressure gradient determines the direction of flow from higher to lower pressure. When the heart contracts, pressure in the ventricles increases. This pressure is used to overcome the resistance of flow or resistance to flow through the blood vessels. Dear students, kinetic energy or pressure, they both control the flow of blood and flow of blood in both factors equally depend on each other. When blood is ejected through pressure into the aorta, the pressure is converted into kinetic energy. This energy sets the blood into motion. Kinetic energy is highest in the aorta then it keeps on decreasing through the arteries and it becomes negligible in the capillaries. So velocity of flow is highest in the aorta and lowest in the capillaries. Dear students, the relationship between pressure and flow in rigid tubes is described by Poiseville's law. Poiseville's law states that the flow of or flow rate of a fluid represented by q is directly proportional to the pressure difference along the length of the tube and it is also directly proportional to the fourth power of the radius of the tube. The flow rate is inversely proportional to two factors that is tube length and fluid viscosity eta. Dear students, Poiseville's equation applies to steady flows in continuous flows in straight rigid tubes. However, blood vessels are not rigid tubes and also the flow of blood is not continuous but it is pulsatile. So, Poiseville's equation does not accurately describe the pressure flow relationship in blood vessels. So, it is used in a modified form for the blood flow in blood vessels. Dear students, the modified form of the Poiseville's equation includes calculation and addition of a non-dimensional constant alpha. This alpha indicates deviation of Poiseville's law in blood vessels. The modified equation of Poiseville's law for blood flow in blood vessels is read as the alpha is equal to the radius of the vessel multiplied by the under root of 2 pi multiplied by various factors specific to the blood vessels that include the harmonic component, the frequency of oscillation represented by F and the density of blood represented by the Greek word rho in sabka under root divided by the viscosity of the blood represented by eta. Is teresi jo alpha calculates that is added to the normal equation of Poiseville or as a result we can get the correct flow of flow rate of blood in blood vessels.