The study of the global scaling relations of disk galaxies is of paramount relevance for understanding the nature, formation, and evolution of these galaxies. I will present here an unified study of the scaling relations in bands B and K and in stellar and baryonic quantities by using a sample of disk galaxies that spans a wide range in morphological types, surface brightnesses and colors. I will also discuss the viability of the secular bulge formation scenario and its potential effect in changing the disk structural properties.