Pinealocytes are the main cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s of the pineal gland

Pineal gland

The pineal gland is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions...

. They produce and secrete melatonin

Melatonin

Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...

. 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

Serotonin

Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

 to melatonin.

Pinealocytes secrete their melatonin into capillaries via long cytoplasmic processes that resemble the axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s of neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s. Secretion of melatonin is stimulated by sympathetic

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

 innervation from superior cervical ganglion

Superior cervical ganglion

The superior cervical ganglion , the largest of the cervical ganglia, is placed opposite the second and third cervical vertebræ. It contains neurons that supply sympathetic innervation to the face....

. They also have shorter cytoplasmic processes that connect to adjacent pinealocytes via desmosome

Desmosome

A desmosome , also known as macula adherens , is a cell structure specialized for cell-to-cell adhesion...

s and gap junction

Gap junction

A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....

s.

Pinealocytes have large irregularly shaped nuclei

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 with prominent nucleoli.