The smooth endoplasmic reticulum synthesizes and stores lipids in animal cells. This organelle also creates and stores steroids to be utilized as hormones throughout the body.
The smooth endoplasmic reticulum has a double membrane that forms sacs known as cisternae. The double membrane and cisternae give the organelle an appearance that is similar to tubes within the cytoplasm of the cell. Another type of endoplasmic reticulum known as the rough endoplasmic reticulum is also found in animal cells. The rough endoplasmic reticulum is essential for synthesizing and packaging proteins within the cell. Both the lipids and the proteins packaged by the smooth and rough endoplasmic reticulum are eventually secreted through vesicles from the cell.