Pars nervosa, neurohypophysis
). Masson trichrome stain,
is an outgrowth of the diencephalon
and includes the
. The median eminence is the termina-
tion site of short axons carrying factors from the arcuate
nuclei that regulate activity of cells in the
Long axons from the
the hypothalamus pass through the
nate in the pars nervosa (Fig. 17-3A). The
Precursors of hormones (
carrier proteins (
) 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.
are large dilated axon terminal endings that are ± lled with
accumulated neurosecretory granules.
are glial cells
that provide support and nutrition to the axons of the neurons.
Pars nervosa, posterior pituitary gland.
30,000; inset (
) Masson trichrome stain,
Major components of the
can be seen in this electron micrograph.
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
in ordinary sections for light microscopy. The vesicles have been transported in
to this site from
, where they were constructed in the cell bodies of the neurons.
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
. 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
, 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.