The pineal gland (also called the pineal body) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles. The shape of the gland resembles a pine cone, which gives it its name.
The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. It is one of the neuroendocrine secretory circumventricular organs in which capillaries are mostly permeable to solutes in the blood.
The pineal gland is present in almost all vertebrates, but is absent in protochordates, in which there is a simple pineal homologue. The hagfish, archaic vertebrates, lack a pineal gland. In some species of amphibians and reptiles, the gland is linked to a light-sensing organ, variously called the parietal eye, the pineal eye or the third eye. Reconstruction of the biological evolution pattern suggests that the pineal gland was originally a kind of atrophied photoreceptor that developed into a neuroendocrine organ.
Galen in the 2nd century C.E. could not find any functional role and regarded the gland as a structural support for the brain tissue. He gave the name konarion, meaning small cone or pinecone,. which during the Renaissance was translated into Latin as pinealis. The 17th-century philosopher René Descartes regarded the gland as the primary locus of mind-body interaction, describing it as the "principal seat of the soul".
Etymology The word pineal (, ), refers to the cone-like shape of the gland, as first used in the 17th century. The term gland derives from the Old French from the 13th century, extended from the Latin to represent an acorn shape.
Structure The pineal gland is a pine cone-shaped (hence the name), unpaired midline brain structure. It is reddish-gray in colour and about the size of a grain of rice (5–8 mm) in humans. It forms part of the epithalamus. It is attached to the rest of the brain by a pineal stalk. The ventral lamina of the pineal stalk is continuous with the posterior commissure, and its dorsal lamina with the habenular commissure.
Location It normally lies in a depression between the two superior colliculi. It is situated between the laterally positioned thalamic bodies, and posterior to the habenular commissure. It is located in the quadrigeminal cistern behind the third ventricle, enclosing the pineal recess.
Blood supply Unlike most of the mammalian brain, the pineal gland is not isolated from the body by the blood–brain barrier system; it has profuse blood flow, second only to the kidney,Arendt J: Melatonin and the Mammalian Pineal Gland, ed 1. London. Chapman & Hall, 1995, p 17 supplied from the choroidal branches of the posterior cerebral artery.
Afferents The afferent nerve supply of pineal gland is by the nervus conarii which receives postganglionic sympathetic afferents from the superior cervical ganglion, and parasympathetic afferents from the pterygopalatine ganglia and otic ganglia. According to research on animals, neurons of the trigeminal ganglion that are involved in pituitary adenylate cyclase-activating peptide neuropeptide signaling project the gland.
Neural pathway for melatonin production
The canonical neural pathway regulating pineal melatonin production begins in the eye with the intrinsically photosensitive ganglion cells of the retina which project inhibitory GABAergic efferents to the paraventricular nucleus of hypothalamus via the retinohypothalamic tract. The paraventricular nucleus in turn projects to the superior cervical ganglia, which finally projects to the pineal gland. Darkness thus leads to disinhibition of the paraventricular nucleus, leading it to activate pineal gland melatonin production by way of the superior cervical ganglia.
Microanatomy
The pineal body in humans consists of a lobular parenchyma of pinealocytes surrounded by connective tissue spaces. The gland's surface is covered by a pial capsule.
The pineal gland consists mainly of pinealocytes, but four other cell types have been identified. As it is quite cellular (in relation to the cortex and white matter), it may be mistaken for a neoplasm.
Cell type Description Pinealocytes The pinealocytes consist of a cell body with 4–6 processes emerging. They produce and secrete melatonin. The pinealocytes can be stained by special silver impregnation methods. Their cytoplasm is lightly basophilic. With special stains, pinealocytes exhibit lengthy, branched cytoplasmic processes that extend to the connective septa and its blood vessels. Interstitial cells Interstitial cells are located between the pinealocytes. They have elongated nuclei and a cytoplasm that is stained darker than that of the pinealocytes. Perivascular phagocyte Many capillaries are present in the gland, and perivascular phagocytes are located close to these blood vessels. The perivascular phagocytes are antigen presenting cells. Pineal neurons In higher vertebrates neurons are usually located in the pineal gland. However, this is not the case in rodents. Peptidergic neuron-like cells In some species, neuronal-like peptidergic cells are present. These cells might have a paracrine regulatory function.
Development The human pineal gland grows in size until about 1–2 years of age, remaining stable thereafter, although its weight increases gradually from puberty onwards. The abundant melatonin levels in children are believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced.
Symmetry In the zebrafish the pineal gland does not straddle the midline, but shows a left-sided bias. In humans, functional cerebral dominance is accompanied by subtle anatomical asymmetry.
Function A principal function of the pineal gland is to produce melatonin, which has various functions in the central nervous system, the most important of which is to help modulate sleep patterns; melatonin production is stimulated by darkness and inhibited by light. Intrinsically photosensitive retinal ganglion cells in the retina detect light and send this signal to the suprachiasmatic nucleus (SCN), synchronizing the SCN to the day-night cycle. Fibers then relay the daylight information to the paraventricular nuclei and spinal cord via the sympathetic nervous system to the superior cervical ganglia, and then to the pineal gland.
Regulation of the pituitary gland Studies on rodents suggest that the pineal gland influences the pituitary gland's secretion of the sex hormones, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Pinealectomy performed on rodents produced no change in pituitary weight, but caused an increase in the concentration of FSH and LH within the gland.
The pineal gland contains receptors for the regulatory neuropeptide endothelin 1, which, when injected in picomolar quantities into the lateral cerebral ventricle, causes a calcium-mediated increase in pineal glucose metabolism.
Clinical significance Calcification Calcification of the pineal gland is typical in young adults, and has been observed in children as young as two years of age. Pineal gland calcification is detrimental to its ability to synthesize melatonin, although it remains inconclusive whether pineal calcification causes sleep problems.
The calcified gland is often seen in skull X-rays. Calcification rates vary widely by country and correlate with an increase in age, with calcification occurring in an estimated 40% of Americans by age seventeen. Calcification of the pineal gland is associated with corpora arenacea, also known as "brain sand".
Tumors Tumors of the pineal gland are called pinealomas. These tumors are rare and 50% to 70% are germinomas that arise from sequestered embryonic germ cells. Histologically they are similar to testicular seminomas and ovarian dysgerminomas.
A pineal tumor can compress the superior colliculi and pretectal area of the dorsal midbrain, producing Parinaud's syndrome. Pineal tumors also can cause compression of the cerebral aqueduct, resulting in a noncommunicating hydrocephalus. Other manifestations are the consequence of their pressure effects and consist of visual disturbances, headache, mental deterioration, and sometimes dementia-like behaviour.
These neoplasms are divided into three categories: pineoblastomas, pineocytomas, and mixed tumors, based on their level of differentiation, which, in turn, correlates with their neoplastic aggressiveness. The clinical course of patients with pineocytomas is prolonged, averaging up to several years. The position of these tumors makes them difficult to remove surgically.
Other conditions The morphology of the pineal gland differs markedly in different pathological conditions. For instance, it is known that its volume is reduced in both obese patients and those with primary insomnia.
Other animals Nearly all vertebrate species possess a pineal gland. The most important exception is a primitive vertebrate, the hagfish. Even in the hagfish, however, there may be a "pineal equivalent" structure in the dorsal diencephalon. A few more complex vertebrates have lost pineal glands over the course of their evolution. The lamprey (another primitive vertebrate), however, does possess one. The lancelet Branchiostoma lanceolatum, an early chordate which is a close relative to vertebrates, also lacks a recognizable pineal gland. Protochordates in general do not have the distinct structure as an organ, but they have a mass of photoreceptor cells called lamellar body, which is regarded as a pineal homologue.
The results of various scientific research in evolutionary biology, comparative neuroanatomy and neurophysiology have explained the evolutionary history (phylogeny) of the pineal gland in different vertebrate species. From the point of view of biological evolution, the pineal gland is a kind of atrophied photoreceptor.Kasal K. "Four-eyed Cambrian fish fossils hint at origins of vertebrate pineal complex". phys.org 22 January 2026 In the epithalamus of some species of amphibians and reptiles, it is linked to a light-sensing organ, known as the parietal eye, which is also called the pineal eye or third eye. It is likely that the common ancestor of all vertebrates had a pair of photosensory organs on the top of its head, similar to the arrangement in modern lampreys. In many lower vertebrates (such as species of fish, amphibians and lizards), the pineal gland is associated with parietal or pineal eye. In these animals, the parietal eye acts as a photoreceptor, and hence are also known as the third eye, and they can be seen on top of the head in some species. Some extinct Devonian fishes have two parietal foramina in their skulls, suggesting an ancestral bilaterality of parietal eyes. The parietal eye and the pineal gland of living tetrapods are probably the descendants of the left and right parts of this organ, respectively. In support of this explanation, the fossil vertebrate Haikouichthys seems to have possessed four eyes.
During embryonic development, the parietal eye and the pineal organ of modern lizards and tuataras form together from a pocket formed in the brain ectoderm. The loss of parietal eyes in many living tetrapods is supported by developmental formation of a paired structure that subsequently fuses into a single pineal gland in developing embryos of turtles, snakes, birds, and mammals.
The pineal organs of mammals fall into one of three categories based on shape. Rodents have more structurally complex pineal glands than other mammals.