Endocrine System > Hypothalamus and Pituitary

Histology of the Neurohypophysis

The neurohypophysis is known also as the pars nervosa. Anatomists distinguish between three areas of this organ, starting closest to the hypothalamus:

The infundibular process froms the bulk of the neurohypophysis is what is usually referred to as the posterior pituitary.

The bulk of the neurohypophysis is composed on largely unmyelinated axons from hypothalamic neurosecretory neurons. These axons have their cell bodies in the paraventricular and supraoptic nuclei of the hypothalamus. These neurons secrete oxytocin or antidiuretic hormone. Roughly 100,000 axons participate in this process to form the posterior pituitary. In addition to axons, the neurohypophysis contains glial cells and other poorly-defined cells called called pituicytes.

In comparison to the adenohypophysis, the histologic appearance of the neurohypophysis is rather ... uninspiring. As shown the in the following images of pars nervosa, large numbers of axons are observed, sprinkled with glial cells and capillaries.

The neurohypophysis contains abundant capillaries, particularly in its ventral portion where most hormone release occurs. Many of these capillaries are fenestrated (contain holes), facilitating delivery of hormones into blood. In the following image, a small section of pars intermedia is visible in the lower left corner.

An interesting histologic feature of the neurohypophysis is the presence of Herring bodies. When viewed with an electron microscope, these are dilated areas or bulges in the terminal portion of axons that contain clusters of neurosecretory granules. The granules contain oxytocin or antidiuretic hormone, along with their associated neurophysins. Herring bodies often are seen in association with capillaries. They are somewhat difficult to identify unambiguously by light microscopy; in the image to the right, the label might better say "probable Herring bodies".

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