Human Physiology, 14th edition (2016)

Cell Structure and Genetic Control 61

Golgi Complex

The Golgi complex, also called the Golgi apparatus, consists of
a stack of several flattened sacs ( fig.  3.12 ). This is something like
a stack of pancakes, but the Golgi sac “pancakes” are hollow, with
cavities called cisternae within each sac. One side of the stack faces
the endoplasmic reticulum and serves as a site of entry for vesicles
from the endoplasmic reticulum that contain cellular products. The
other side of the stack faces the plasma membrane, and the cellular
products somehow get transferred to that side. This may be because
the products are passed from one sac to the next, probably in ves-
icles, until reaching the sac facing the plasma membrane. Alter-
natively, the sac that receives the products from the endoplasmic
reticulum may move through the stack until reaching the other side.
By whichever mechanism the cell product is moved
through the Golgi complex, it becomes chemically modified
and then, in the sac facing the plasma membrane, is packaged
into vesicles that bud off the sac. Depending on the nature of
the cell product, the vesicles that leave the Golgi complex may
become lysosomes, or secretory vesicles (in which the product
is released from the cell by exocytosis), or may serve other
functions. The scientists who discovered how secretory vesi-
cles dock with their correct target membranes were awarded
the 2013 Nobel Prize in Physiology or Medicine.

reactions in steroid hormone production and inactivation, for
example, and a site for the storage of Ca^2 1 in striated muscle
cells. The granular endoplasmic reticulum is abundant in cells
that are active in protein synthesis and secretion, such as those
of many exocrine and endocrine glands.

CLINICAL APPLICATION

Proliferation of the agranular endoplasmic reticulum of liver

cells can occur in response to the abuse of alcohol and

drugs. The agranular endoplasmic reticulum has numer-

ous functions, including the enzymatic modification of toxic

compounds into less toxic, more water-soluble derivatives

that can be more easily excreted. Partly because of these

enzymes, a person may gain tolerance to a drug, requir-

ing a higher dose of the abused substance to produce the

same effect. For example, a greater amount of the enzyme

alcohol dehydrogenase will result in a faster elimination of

alcohol. Tolerance to alcohol and barbiturates can over-

lap because of overlapping specificities of the detoxifying

enzymes.

Clinical Investigation CLUES

George’s liver cells show an unusually extensive agranu-

lar (smooth) endoplasmic reticulum.

• How does this relate to liver function, his symptoms,
  and what he told his doctor? Nucleus

Lysosome

Cytoplasm

(b)

(a)

Plasma

Secretion

Secretory

storage

Golgi complex

Cisternae

Ribosomes

Protein

Granular

endoplasmic

reticulum

Figure 3.12 The Golgi complex. ( a ) An electron

micrograph of a Golgi complex. Notice the formation of vesicles

at the ends of some of the flattened sacs. ( b ) An illustration of the

processing of proteins by the granular endoplasmic reticulum and

Golgi complex.