CHAPTER 17
Endocrine System
339
Superior
colliculus
Posterior
commissure
Pineal
gland
Capsule
Septum
Brain
sand
A
Brain sand
Brain sand
Brain sand
Pinealocytes
Pinealocytes
Pinealocytes
Pinealocytes
Pinealocytes
Pinealocytes
Capillary
Capillary
Capillary
Capillary
Capillary
Capillary
Neuroglial
Neuroglial
cells
cells
Neuroglial
cells
Brain
Brain
sand
sand
Brain
sand
Neuroglial
Neuroglial
cells
cells
Neuroglial
cells
B
Pineal Gland
Figure 17-13A.
Overview of the pineal gland.
H&E,
3
5
The
pineal gland
is a pinecone-shaped neuroendocrine gland about 8 mm
in length that produces
melatonin
and is covered by a capsule of pia mater.
The pineal gland is part of the epithalamus (a diencephalic structure) that
extends caudally from its attachment immediately superior to the poste-
rior commissure into the superior (quadrigeminal) cistern. It is superior
to the colliculi of the midbrain. Secretion of melatonin is stimulated by
darkness and inhibited by light. The level of this hormone increases dur-
ing sleep. Connective septa divide the pineal into poorly deF ned lobules.
This gland contains
pinealocytes
,
neuroglial cells
, and
blood vessels
.
CalciF ed concretions called
brain sand
(also called
corpora arenacea
)
may also be present in the pineal gland, especially in older patients.
Figure 17-13B.
Pinealocytes and brain sand of the pineal gland.
H&E,
3
140; insets
3
363
The
pineal gland
is composed of two types of cells:
pinealocytes
and
neuroglial cells
. The
pinealocytes
are modiF ed neurons, which have
round or ovoid nuclei with pale-stained cytoplasm containing granules
F lled with
melatonin
. The pinealocytes synthesize
melatonin
, which is
important in the regulation of the
circadian rhythms
(day and night
cycles). The pinealocytes are larger than the neuroglial cells and have
a long cytoplasmic process that extends to the capillaries; their secre-
tory granules are released into the capillaries. The
neuroglial cells
are
supportive cells with small, dark nuclei. They are also called
pineal
astrocytes
and are commonly found near the capillaries. The particles
of brain sand assume various sizes as shown here; their function is not
known. Other functions of the pineal gland may relate to promoting
sleep and sexual development; enhancing mood and slowing the aging
process; and, possibly, inhibiting the growth of some tumors.
The
calci± cations
(
brain sand
) within the pineal gland increase with
age. These calciF cations appear white in computed tomography
scan and magnetic resonance imaging and are commonly used as a
natural landmark by radiologists and neurologists.
CLINICAL CORRELATION
Figure 17-13C.
Pineoblastoma.
Immunohistochemical preparation
for synaptophysin,
3
198
Pineoblastoma
is an aggressive malignant tumor in children, which
arises in the pineal gland. Because it commonly consists of cellular
sheets that lack an architectural pattern, it is described as a
small blue
cell tumor
. The term
embryonal
is also used to emphasize the rudi-
mentary developmental stage of the tumor, although in some tumors
the cells begin to show differentiation into neurons, or glial cells, or
even rods and cones. The earliest stages of such specialization may
be detectable before any architectural alteration.
Synaptophysin
is a
protein associated with synapses. An antibody to this marker protein,
conjugated to the enzyme peroxidase, creates a colored metabolite
wherever synaptophysin appears in cell cytoplasm or membranes. In
the image on the
left
, a brown compound marks the
tumor cells
that
contain synaptophysin. Tumor treatments can be individually formu-
lated based on the different cellular components.
Tumor
Nucleus of
tumor cell
Synaptophysin in
tumor cell cytoplasm
C
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