ER is an inner connected system of membrane- bound channels in the cytoplasm of the cells.
There are three structural elements of ER :
(i) Cisternae: The cisternae are broad flat membrane bound space arranged parallel to each other to form lamellae. e.g., Pancreas and liver cells.
(ii) Vesicles: The vesicles are spherical spaces (25-500 nm in diameter).
(iii) Tubules: The tubules are less small and branched tubular spaces found in cells which synthesize steroids and are 50-100 nm in diameter.
Fig.(a) Cisternae
Fig.(b) Vesicles
Fig.(c) Tubules
