A simple model of pressure-flow relationship in blood vessels was developed. The calculation of the model components was based on velocity profiles in the vessels. The flat velocity profile in the entrance of the vessel was considered. By using mean pressure over the cross-section and assuming a polynomial approximation of the velocity profile, it is shown that the resistance of a vessel segment increases with increased flatness of the velocity profile. Moreover, the analysis provides a means to calculate the resistance of a vessel segment based on the shape of the velocity profiles in that segment. The analysis shows that the inertance element of the segment is not affected by the shape of the velocity profile.