Page 80 - Atlas of Histology with Functional Correlations

mitochondria utilization are synthesized by the free ribosomes that are

scattered within the cell cytoplasm.

SMOOTH ENDOPLASMIC RETICULUM

Although the smooth endoplasmic reticulum (SER) is continuous with the
RER, its membranes lack ribosomes, and therefore, its functions are
completely different and unrelated to protein synthesis. SER is found in
abundance in cells that synthesize phospholipids that constitute all cell

membranes, cholesterol, and steroid hormones, such as estrogens,
testosterone, and corticosteroids. When liver cells (hepatocytes) are exposed
to potentially harmful drugs and chemicals, SER proliferates and inactivates

or detoxifies the chemicals. Similarly, in hepatocytes, SER is involved in
carbohydrate metabolism that converts glycogen to glucose. Skeletal and
cardiac muscle fibers also exhibit an extensive network of SER, called
sarcoplasmic reticulum, whose primary functions is calcium storage
(sequestering) between contractions and calcium release for initiation of

muscular contractions.

Golgi Apparatus

The Golgi apparatus (also known as Golgi complex or Golgi body) is also
composed of a system of membrane-bound, smooth, flattened, stacked, and
slightly curved cisternae. These cisternae, however, are separate from those of
endoplasmic reticulum. In most cells, there is a polarity in the Golgi apparatus.
Near the Golgi apparatus, numerous small vesicles with newly synthesized

proteins bud off from the rough endoplasmic reticulum and move to the Golgi
apparatus for further processing. The Golgi cisternae nearest the budding
vesicles are the forming, convex, or the cis face of the Golgi apparatus. The

opposite side of the Golgi apparatus is the maturing inner concave side or the
trans face. Vesicles from the endoplasmic reticulum move through the
cytoplasm to the cis side of the Golgi apparatus and bud off from the trans side
for transport of proteins to different sites in the cell cytoplasm.

FUNCTIONAL CORRELATIONS 2.3 ■ Golgi

Apparatus

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