medicinal plants top

Agranular (Smooth) Endoplasmic Reticulum (sER)


Agranular (Smooth) Endoplasmic Reticulum (sER)


The morphological difference between smooth or agranular ER and the granular

form of ER is the absence of ribosomes. Rough ER proliferates to smooth

ER, where the synthesis of lipid and steroid molecules occurs, cholesterol

among others. In addition, sER metabolizes many xenobiotic substances,

such as pharmaceuticals, pesticides and carcinogens, etc. The sER is therefore

the most important intracellular detoxification system. It usually takes the

form of a tightly woven network of branched tubules of various diameters

(30–100nm). Cisternae are usually absent. As in liver cells, for example,

rough and smooth ER are often confluent. There is a pronounced expansion

of the agranular ER (sER) in steroid hormone-producing cells, particularly in

cells of the adrenal cortex, the corpus luteum and in the interstitial cells of

the testes. Smooth ER is called sarcoplasmic reticulum in striated skeletal

muscle tissue, where it serves to store calcium.

In this picture of an ovarian cell from the corpus luteum, the sER forms many

membrane layers around a mitochondrion


Dependent on the cell type, the morphology of smooth (agranular) ER may

vary considerably. The fixation technique will obviously influence the preservation

and electron-microscopic presentation of the delicate membrane

system as well. In this figure, the tubules of the agranular ER are arranged in

loops and meandering lines. Note the only marginally stained cytoplasm

between the tubules.

Striated muscle cells are also interspersed with smoothly lined tubules (Tand

L-system) All tubules combined form the sarcoplasmic reticulum

of muscle cells or muscle fibers. This highly organized system of tubules

exists in a characteristic relationship with the striation pattern of the

myofibrils, and both combined will form impressive patterns.

Partial section of the perikaryon of a sensory cell from the rat Jacobson organ


Annulate Lamellae


Annulate lamellae are a specialized form of smooth endoplasmic reticulum

membrane. They articulate from the nuclear membrane and form concentric

layers of lamellae or, as seen here, membrane stacks. The cisternae show porecomplexes

1 , which are identical to those of the nuclear pore complexes

(cf. Fig.11). Osmiophilic material is more abundant in the pore regions.

Annulate lamellae are prevalent in cells with a high membrane turnover,

such as tumor cells, testicular Sertoli cells and gametes. This figure shows details

from a human oocyte.