Pinealocytes are the main cells of the pineal gland. They produce and secrete melatonin. Pinealocytes have an organelle called the synaptic ribbon; this is considered to be a specific marker for pinealocytes. Some of the enzymes of the pinealocytes include 5-HT N-acetyl transferase and 5-hydroxyindole-O-methyltransferase which are used to convert serotonin to melatonin.
Pinealocytes secrete their melatonin into capillaries via long cytoplasmic processes that resemble the axons of neurons. Secretion of melatonin is stimulated by sympathetic innervation from superior cervical ganglion. They also have shorter cytoplasmic processes that connect to adjacent pinealocytes via desmosomes and gap junctions.
Pinealocytes have large irregularly shaped nuclei with prominent nucleoli.
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