Sep 262012

Endoplasmic Reticulum is one of the most important parts of a cell (the functional and basic unit of life). It conducts various functions in a cell which helps the cell to work in an efficient and smooth manner. It is known as E.R. in abbreviated form. It is a complex system of membranes which runs throughout the cytoplasm of all eukaryotic cells except mature R.B.C. of mammals, eggs and other embryonic cells.

It was first discovered by Porter in the year 1945 A.D. Endoplasmic Reticulum is extensive or well-developed in metabolically active cells such as liver cells, pancreatic cells etc. But Endoplasmic Reticulum is simple in storage cells like adipose cells. It is generally connected with nuclear membranes and sometimes extended upto the cell membranes.

Endoplasmic Reticulum occurs in three different morphological forms which can be enlisted as:

  1. Cisternae
  2. Vesicles
  3. Tubules

1. Cisternae
Cisternae are elongated, flat, sac-like unbranched structures which are bounded by single membrane. These structures are generally found to be parallel to each other. They are about 40 to 50mμ in diameter. Cisternae are generally covered with ribosomes.

2. Vesicles
Vesicles are round, oval or spherical, membrane-bound structures which are found in the cytoplasm of cell. They are about 25-50mμ in diameter. They do not contain ribosomes in them.

3. Tubules
Tubules are branched, irregular structures which form a reticular or net-like structure along with the cisternae. They are about 50-200mμ in diameter.

Types of Endoplasmic Reticulum (E.R.)
There are two types of Endoplasmic Reticulum. They are:

  • Smooth Endoplasmic Reticulum (S.E.R.): If endoplasmic reticulum is not associated with ribosomes, it is called smooth endoplasmic reticulum. It has a smooth membrane. It doesn’t participate actively in the process of protein-synthesis. It is associated with the synthesis of steroids and lipids. It is connected with Golgi bodies and plasma membrane.
  • Rough Endoplasmic Reticulum (R.E.R.): If endoplasmic reticulum is associated with ribosomes, it is called rough endoplasmic reticulum. It has a rough and granular surface due to the presence of ribosomes. It mainly contains cisternae and few tubules. It participates actively in protein-synthesis process. It is connected with nuclear membrane.

Functions of Endoplasmic Reticulum
The functions of Endoplasmic Reticulum are given below:

  • Endoplasmic Reticulum (E.R.) gives mechanical support by forming a network in the cytoplasm.
  • It helps in the formation of an intracellular transport system which leads to the exchange of materials from one part of the cell to another.
  • It consists of many enzymes which helps in performing many metabolic activities. It also produces enzymes of primary lysosomes.
  • It helps in protein-synthesis by Rough Endoplasmic Reticulum (R.E.R.). It also helps in the synthesis of lipids and steroids by Smooth Endoplasmic Reticulum (S.E.R.).
  • It helps in the exchange of materials between the cells and the immediate environment.
  • It helps in the formation of nuclear membrane, cell membrane and cell wall also.