Endoplasmic Reticulum

            The cytoplasmic matrix contains a complex network of interconnecting membrane-bound vacuoles or cavities. These cavities often remain concentrated in the endoplasmic portion of the cytoplasm; therefore, known as endoplasmic reticulum, a name derived from the fact that in the light microscope it looks like a net in the cytoplasm.

           The name "endoplasmic reticulum" was coined in 1953 by Porter, who in 1945 had observed it in electron micrographs of liver cells.

OCCURRENCE:

       The endoplasmic reticulum is a cell organelle. It occurs varies from cell to cell. The RBC, eg, embryonic cells lack in ER. Which produce only proteins to be retained in the cytoplasmic matrix, the ER is poorly developed, although the cell may contain many ribosomes. The ER contains two types of the ribosome is Smooth endoplasmic reticulum (SER) and Rough endoplasmic reticulum (RER). The adipose tissues, brown fat cells, and adrenocortical cells, interstitial cells of testes and cells of corpus luteam of ovaries, sebaceous cells, and retinal pigment cells contain only smooth endoplasmic reticulum. The cells of those organs which are actively engaged in the synthesis of proteins such as the acinar cell of the pancreas, plasma cells, goblet cells, and cells of some endocrine glands are found to contain Rough endoplasmic reticulum.

IMPORTANCE  IN ENDOMEMBRANE  SYSTEM:

    The endoplasmic reticulum is the main component of the endomembrane system, also called the cytoplasmic vacuolar system or concavity network. This system comprises the following structures: 

    1)The nuclear envelope, consisting of two nonidentical membranes one opposed to the nuclear chromatin and the other separated from the first membrane by ap perinuclear space, the two membranes being in contact at the nuclear pores.

     2)The endoplasmic reticulum.

       3) Golgi apparatus, which is mainly related to some of the terminal processes of cell secretion GERL(Golgi, endoplasmic reticulum, and lysosome).

MORPHOLOGY: 

Morphologically, the endoplasmic reticulum may occur in the following three forms :

   1)Lamellar form or cisternae.

    2) Vesicular form or vesicles.

    3) Tubular form of tubules

            The cisternae are long, flattened, sac-like, unbranched tubules having a diameter of 40 to 50nm. They parallelly in bundles or stakes.

      The vesicles are oval, membrane-bound vacuolar structures having a diameter of 25 to 500 nm. They often remain isolated in the cytoplasm and occur in more cells but especially abundant in the SER. The tubules are branched structures forming the reticular system along with the cisternae and vesicles. They usually have a diameter from 50 to 190 nm and occur almost in all the cells.