332
UNIT 3
Organ Systems
Lumen of
Lumen of
small vein
small vein
Lumen of
small vein
Herring
Herring
bodies
bodies
Herring
bodies
Capillary
Capillary
Capillary
Pituicytes
Pituicytes
Pituicytes
A
Figure 17-6A.
Pars nervosa, neurohypophysis
(
posterior
pituitary gland
). Masson trichrome stain,
3
281
The
neurohypophysis
is an outgrowth of the diencephalon
and includes the
median eminence
, the
infundibular stalk
,
and the
pars nervosa
. The median eminence is the termina-
tion site of short axons carrying factors from the arcuate
nuclei that regulate activity of cells in the
adenohypophysis
.
Long axons from the
supraoptic
and
paraventricular nuclei
of
the hypothalamus pass through the
infundibular stalk
and termi-
nate in the pars nervosa (Fig. 17-3A). The
pars nervosa
contains
unmyelinated axons
,
axon terminals
,
pituicytes
, and
capillaries
.
Precursors of hormones (
ADH/vasopressin
and
oxytocin
) and
carrier proteins (
neurophysins
) are synthesized in the cell bodies
of neurons in the two hypothalamic nuclei and are transported
through the axons in the infundibular stalk to the axon terminal
endings in the pars nervosa, where processing is completed and
secretion occurs adjacent to fenestrated capillaries.
Herring bod-
ies
are large dilated axon terminal endings that are ± lled with
accumulated neurosecretory granules.
Pituicytes
are glial cells
that provide support and nutrition to the axons of the neurons.
Herring
body
Pituicyte
Fenestrated capillary
Axon terminals
Pituicyte
B
Figure 17-6B.
Pars nervosa, posterior pituitary gland.
EM,
3
30,000; inset (
color
) Masson trichrome stain,
3
791
Major components of the
posterior lobe
can be seen in this electron micrograph.
Terminals
of hormone secreting neurons are seen
as vesicle-± lled, membrane-bounded pro± les of widely varying shapes and sizes. The largest, most distended pro±
les appear as
Herring bodies
in ordinary sections for light microscopy. The vesicles have been transported in
unmyelinated axons
to this site from
the
supraoptic
and
paraventricular nuclei
of the
hypothalamus
, where they were constructed in the cell bodies of the neurons.
ADH
or
oxytocin
is released when action potentials are conducted from the hypothalamus in response to neural signals acting on the cell
bodies and dendrites in the hypothalamus. The two secreted hormones have only a short distance to diffuse to reach the wall of a
fenestrated capillary
. There are no neuronal cell bodies in the posterior lobe, so any nuclei seen in the posterior lobe most likely will
belong either to endothelial cells of capillaries or to
pituicytes
, as is the case with the nucleus in this view. Like astrocytes in other
parts of the central nervous system, pituicytes have processes that contact nerve processes and the walls of capillaries.
previous page 347 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online next page 349 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online Home Toggle text on/off