Decreasing power is available in a cell both as NADPH and NADH but these have quite distinct roles. NADH is oxidized by the respiratory chain to produce ATP by oxidative phosphorylation. For biosynthetic reactions NADPH is used which decreasing needs power. Despite their similar structures, NADPH and NADH are not metabolically interchangeable and so the cell must carry out a group of reactions which specially establish NADPH. This set of reactions is the pentose phosphate pathway also called as the hexose monophosphate shunt or the phosphogluconate pathway. It took place in the cytosol and is particularly significant in tissues like as mammary gland, adipose tissue and  the  adrenal  cortex  which  synthesizes  fatty  acids  and  steroids  from acetyl CoA. The activity of the pathway is very low in skeletal muscle, for instance, that does not synthesize fatty acids or steroids.