The endoplasmic reticulum (ER) is a continuous network of parallel membranes within the cytosol of the cell. In many electron micrographs it appears to be discontinuous due to the fact that these pictures are made using extremely thin slices through cells. Because of this the three dimensional nature of the ER is often not clearly seen. In reality the ER is something like an extremely complex tunnel system which is involved in the transport and synthesis of materials important in the life of the cell.
In the majority of metabolically inactive cells there is very little ER present. However cells which synthesise and secrete protein containing molecules have vast amounts of ER present.
There are two distinct types of ER the rough endoplasmic reticulum and the smooth endoplasmic reticulum. It is important to remember that the two types are continuous with each other and that they are in a dynamic state. Rough ER can change to Smooth ER and vice versa depending on the activities of the cell concerned.
Smooth endoplasmic reticulum is present in relatively small quantities in most cells. The exception being cells which are actively involved in secreting or processing lipids (fats).
Smooth ER is also important clinically as it has a role in the break down of drugs and medicines in the liver. The liver is a major detoxification centre within the human body and it's cells contain substantial amounts of smooth ER. It is known from experiments that the amount of smooth ER present in the liver increases in response to the administration of certain drugs such as phenobarbitones.
Smooth ER has a third important role connected with calcium storage in muscle cells which has an affect on muscular contraction and hence body movements.
Rough endoplasmic reticulum is so called because it has a granular appearance due to the abundant presence of tiny organelles called ribosomes which comprise of protein and RNA (ribonucleic acid).
The function of ribosomes is to produce proteins. Not all of the ribosomes are attached to the ER some float freely within the cytosol.
The diagram below represents the mechanism of protein production within the cell.
Click here to see a simple animation of this process
This page last updated on Tue Aug 17 12:27:12 BST 2004