The endoplasmatic reticulum is a cell organelle which forms an interconnected network of tubules, vesicles, and cisternae held together by the cytoskeleton within cytoplasm. They play an important role in the synthesis of lipids and proteins to be used in the cell membrane or to be secreted from the cell.
The endoplasmatic reticulum also fulfills other specialized functions to such as sequestration of calcium, and production and storage of glycogen, steroids, and other macromolecules. There are two types of endoplasmatic reticulum: smooth and rough.
Smooth endoplasmatic reticulum is the site of synthesis and digestion of fatty acids and phospholipids. In the liver it is used to modify dangerous chemicals. Rough ER is the site of manufacture of secretory proteins as well as proteins destined to be inserted in the cell membrane. It is rough because of the vast numbers of ribosomes which stud its surface. As these ribosomes build an amino acid chain, it is injected through the endoplasmatic reticulum into the vesicle.
The lacey membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945.