Pineal gland

The nucleus of a pinealocyte is euchromatic with a prominent nucleolus.  The cytoplasm is not evident with conventional stains; however, the cell generally has two or more extensions similar to neuronal processes.  The main secretory product of pinealocytes is melatonin, which regulates light-dark cycles (circadian rhythms).

Interstitial cells, the minor cell type in the pineal, are modified astrocytes similar to pituicytes in the neurohypophysis.  These cells are located within groups of pinealocytes and in the connective tissue septa.  The nuclei of interstitial cells are more elongated and heterochromatic than those of pinealocytes.

Connective tissue septa originate from the pia and project into the gland, carrying with them blood vessels and sympathetic nerve fibers.  Capillaries in the pineal are fenestrated, like those found in other endocrine organs.

Connective tissue septa originate from the pia and project into the gland, carrying with them blood vessels and sympathetic nerve fibers.  Capillaries in the pineal are fenestrated, like those found in other endocrine organs.