<p>cross section: human pineaThe pineal gland is about 8 mm in diameter, encased in a tightly adherent pia mater, and divided into a number of connective tissues wrapped lobes. Small blood vessels may be visible in the septate spaces between the lobes. 
</p><p>The pineal gland is largely composed of two cell types, better distinguished at higher magnifications.
</p><p>Roughly 95% of the pineal gland consists of pinealocytes, the cells that produce the hormone melatonin which works with the hypothalamus to regulate sleep wake cycles. Pinealocytes are arranged in small clusters or rosettes. They can be identified by their large, round, pale staining nuclei, surrounded by wide rims of light staining cytoplasm. In some preparations it may be possible to see long cytoplasmic processes extending from the pinealocytes into the septae.  
</p><p>Closely associated with the pinealocytes are supportive astrocytes with smaller darker nuclei and long cytoplasmic projections.
</p><p>In some parts of the brain and notably the pineal gland, there are large irregularly shaped dark purple staining calcifications termed corpora arenacea or brain sand. These salts of calcium, magnesium and ammonium increase in size and number in the brain with aging but have no know function.gland
magnification: 200x by phase contrast
</p>
hematoxylin eosin stain
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/146824358@N03">Berkshire Community College  Bioscience Image Library</a>
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/146824358@N03/40442210953/">Connective Tissue Wrapped Lobes in Older Human Pineal by Phase Contrast</a>