What are the three structural elements of endoplasmic reticulum ? Explain in short

ER was discovered by Porter (1945) and Thompson (1945) and this name was given by Porter (1945). ER is an inner connected system of membrane-bound channels in the cytoplasm of the cells. There are three structural elements of ER :
(1) Cistemae : The cisternae are broad flat membrane j bound space arranged parallel to each other to form j lamellae, e.g., Pancreas and liver cells.
(2) Vesicles : The vesicles are spherical spaces (25-500 1 nm in diameter).
(3) Tubules : The tubules are less small and branched tubular spaces found in cells which synthesize steroids and are 50-100 nm in diameter.