PINEAL GLAND

Slide # 194 - The most distinguishing feature of the pineal at low power is the appearance of A brain sand @ , extracellular calcified deposits that accumulate with age.   The pineal derives from the neuroectoderm and is surrounded by a thin connective tissue pia mater, which also provides the gland with septa containing blood vessels and largely sympathetic neuronal innervation.

Two predominant cell types exist in the pineal: pinealocytes with larger, paler nuclei and neuroglial cells containing smaller, dark nuclei.   Projections from the suprachiasmatic nucleus (SCN) in the hypothalamus to the pineal are stimulated in the absence of light to release neurosecretory granules containing norepinephrine.   Norepinephrine in turn causes the night-time conversion of serotonin to melatonin within the pinealocyte.   Melatonin is believed to be a molecular mediator of the body = s diurnal rhythms, which are characterized by pulsatile hormone secretion.