338
UNIT 3
Organ Systems
Cell bodies of
Cell bodies of
ganglion neurons
ganglion neurons
Cell bodies of
ganglion neurons
Nerve fibers
Nerve fibers
Nerve fibers
Chromaffin
Chromaffin
cells
cells
Chromaffin
cells
Blood cells
Blood cells
in the vein
in the vein
Blood cells
in the vein
A
Nucleus of chromaffin cell
Nucleolus
Rough
endoplasmic reticulum
Norepinephrine
Norepinephrine
granule
granule
Norepinephrine
granule
Lumen of
L
u
m
e
n
o
f
fenestrated
f
e
n
e
s
t
r
a
t
e
d
capillary
c
a
p
i
l
l
a
r
y
Lumen of
fenestrated
capillary
Chromaffin cells
B
Figure 17-12A.
Adrenal medulla.
H&E,
3
140; inset (
left
)
3
340; inset (
right
)
3
158
The
adrenal medulla
is derived from the neural crest; its embry-
onic origin is different from that of the adrenal cortex. The cells
in the adrenal medulla include
chromaf± n cells
and
ganglion neu-
rons
. Large blood vessels (
veins
) are found in the medulla; these
vessels drain blood out of the adrenal gland. ChromafF n cells are
irregularly shaped neuroendocrine cells and are the predominant
cells in the adrenal medulla. These cells have round nuclei with
pale-staining cytoplasm as shown here. They have numerous
plasma secretory granules that stain intensively with chromium
salts; therefore, they are called
chromaf± n cells
. These cells secrete
the
sympathomimetic
hormones
adrenaline
(
epinephrine
) and
noradrenaline
(
norepinephrine
) in response to stress. The sympa-
thetic ganglion neurons have large cell bodies that are surrounded
by supporting cells as shown in the
left inset
. The adrenal medulla
is innervated by sympathetic preganglionic nerves.
Figure 17-12B.
Cells of the adrenal medulla.
EM,
3
5,700; inset (
color
) H&E,
3
1,632
Cells of the adrenal medulla
synthesize and secrete
adrenaline (epinephrine)
and
noradrenaline (norepinephrine)
, with adrenaline
being the main product. These
catecholamines
are both synthesized from the amino acid
tyrosine
through a series of reactions that
occur in the
cytosol
and within the granules in the cytoplasm. The generation of the granules, along with the enzymes, packag-
ing proteins, and membrane proteins, involves the RER and
Golgi complex
, so these cells have equipment similar to a protein-
synthesizing cell, although their product is not a protein. The granules vary greatly in size and appearance, a refl
ection partly of the
current state of activity (synthesis, storage) and partly of the catecholamine (epinephrine, norepinephrine) stored in the granule. The
granules that store norepinephrine (noradrenaline) are the large electron-lucent proF
les containing a small electron-dense particle at
the edge of the cavity. Like the cells of the cortex, the cells of the adrenal medulla are closely associated with the walls of fenestrated
capillaries. However, the edge of the vessel in the
upper left corner
of this view does not show the fenestrations.
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