Question: why is the nuclear membrane considered part of the endomembrane system

title: Endomembrane system
text: Liver cells are another example of specialized cells that contain an abundance of smooth ER . These cells provide an example of the role of smooth ER in carbohydrate metabolism . Liver cells store carbohydrates in the form of glycogen . The breakdown of glycogen eventually leads to the release of glucose from the liver cells , which is important in the regulation of sugar concentration in the blood . However , the primary product of glycogen breakdown is glucose - 1 - phosphate . This is converted to glucose - 6 - phosphate and then an enzyme of the liver cell 's smooth ER removes the phosphate from the glucose , so that it can then leave the cell .