Pineocyte

Pinealocyte
Cross-section of pineal gland displaying pinealocytes and other cells
Details
System	Endocrine system
Identifiers
Latin	Pinealocytus, endocrinocitus pineale
Code	TH H3.08.02.3.00002
TH	H3.08.02.3.00002
Anatomical terminology []

Pinealocytes are the main cells contained in the pineal gland, located behind the third ventricle and between the two hemispheres of the brain. The primary function of the pinealocytes is the secretion of the hormone melatonin, important in the regulation of circadian rhythms. In humans, the suprachiasmatic nucleus of the hypothalamus communicates the message of darkness to the pinealocytes, and as a result, controls the day and night cycle. It has been suggested that pinealocytes are derived from photoreceptor cells. Research has also shown the decline in the number of pinealocytes by way of apoptosis as the age of the organism increases. There are two different types of pinealocytes, type I and type II, which have been classified based on certain properties including shape, presence or absence of infolding of the nuclear envelope, and composition of the cytoplasm.

Type 1 pinealocytes are also known as light pinealocytes because they stain at a low density when viewed under a light microscope and appear lighter to the human eye. These Type 1 cells have been identified through research to have a round or oval shape and a diameter ranging from 7–11 micrometers. Type 1 pinealocytes are typically more numerous in both children and adults than Type 2 pinealocytes. They are also considered to be the more active cell because of the presence of certain cellular contents, including a high concentration of . Another finding consistent with Type 1 pinealocytes is the increase in the amount of lysosomes and dense granules present in the cells as the age of the organism increases, possibly indicating the importance of autophagocytosis in these cells. Research has also shown that Type 1 pinealocytes contain the neurotransmitter serotonin, which later is converted to melatonin, the main hormone secreted by the pineal gland.