What Is It, Where Is It, Its Function and More
Editors:Alyssa Haag,Stefan Stoisavlijevic, MD,Kelsey LaFayette, DNP, ARNP, FNP-C
Illustrator:Jessica Reynolds, MS
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What is the pineal gland?
The pineal gland is a small, pinecone-shaped neuroendocrine organ whose primary function is the nighttime secretion of melatonin. Melatonin regulates the sleep-wake cycle, also known as the circadian rhythm. The pineal gland receives light information from the retina, which is why the pineal gland is sometimes referred to as the third eye. The pineal gland secretes melatonin during dark periods.
Where is the pineal gland located?
The pineal gland is located in the brain, behind the third cerebral ventricle in the midline and between the two cerebral hemispheres. It is attached to the roof of the third ventricle by a short stalk. The pineal gland is derived from an embryonic structure known as the diencephalon, which also develops into the epithalamus, thalamus, subthalamus, and hypothalamus. It can secrete hormones into the bloodstream as it is not covered by the blood-brain barrier, a physiological barrier formed by endothelial cells.
What is the pineal gland’s function?
The primary function of the human pineal gland is to control the nighttime secretion of melatonin, thereby regulating the circadian system and sleep patterns. Additionally, the pineal gland plays a role in cell protection, neuroprotection, and mood disorders (e.g., schizophrenia and depression). It is also essential for reproduction and in the control of sexual maturation. The pineal gland has been found to inhibit gonadotropin-releasing hormone (GnRH) from the hypothalamus, which ultimately regulates puberty onset, sexual development, and ovulatory cycles in females.
What are disorders of the pineal gland?
Disorders of the pineal gland can occur due to aging, traumatic, and developmental conditions. Examples include pineal tumors, craniopharyngiomas; injuries affecting the sympathetic innervation of the pineal gland; and rare congenital disorders. Conditions that affect the pineal gland alter melatonin secretion and disrupt the circadian cycle.
As humans age, the pineal gland begins to calcify, which increases with advanced age. Calcification of the pineal gland may correlate with the age-related decline in melatonin production and fragmented sleep-wake patterns in the elderly. Also, some studies have found that the degree of calcification is higher in individuals with Alzheimer disease.
Tumors of the pineal gland are uncommon, constituting approximately three percent of brain tumors. Of the types of tumors that can form in the pineal region, germ cell tumors are the most frequent. They are more common in children aged 1 to 12 years and those assigned males at birth. Pineal gland tumors can lead to hydrocephalus, a condition resulting in the buildup of cerebrospinal fluid in the brain. Hydrocephalus presents with headaches, lethargy, and other signs of increased intracranial pressure, such as blurred vision, vomiting, changes in behavior, and weakness with moving or talking. The majority of individuals with pineal tumors have Parinaud syndrome. This neurological condition makes it difficult for the individual to look upwards due to pressure on the pretectal region of the brain (i.e., the dorsal aspect of the upper midbrain).
Another type of tumor affecting the pineal gland is craniopharyngiomas, rare, benign brain tumors that form near the pituitary gland and the hypothalamus. Craniopharyngiomas can occur at any age, but it occurs most often in children aged 5 to 14 and older adults aged 50 to 74. It is usually made of part solid mass and part fluid-filled cysts. As these cysts grow, the intracranial pressure increases, which can cause headaches, nausea, and vomiting. They may also extend to compress the pituitary gland and lead to hormonal dysfunction. Furthermore, it can compress other nearby structures, such as the optic chiasm, where the two optic nerves partially cross, resulting in visual deficits.
The pineal gland receives innervation from the hypothalamus via the spinal cord and the superior cervical ganglion. If a spinal cord injury occurs, the circuits that influence the basal production of pineal gland hormones may be disrupted. This results in tetraplegia, the inability to voluntarily move the upper and lower body parts. There may also be an absence in the pineal production of melatonin, which results in sleep disorders, poor quality of life, increased oxidative stress, and the loss of anti-inflammatory and neuroprotective effects.
Lastly, an example of a congenital pineal gland disorder includes pineal agenesis, or failure of the pineal gland to develop. This has been linked to mutations in the paired box gene 6 (PAX6), which leads to pineal gland abnormalities and other brain and eye abnormalities. PAX6 is responsible for cortical developmental processes, including cellular proliferation, neuronal migration, and axonal guidance. The extent to which pineal agenesis affects human growth and development has not yet been explored extensively. Additional neurological, endocrine, and sleep studies may help provide further insight into the effects on normal human growth and development.
Magnetic resonance imaging (MRI) is the most useful initial study to identify tumors and other pineal gland abnormalities and delineate their relationship to adjacent structures. For example, if a pineal tumor grows and extends into the third ventricle, it can block the flow of the cerebrospinal fluid and cause obstructive hydrocephalus, which can be seen on MRI. Computed tomography (CT) scans can also detect pineal abnormalities. Pineal region tumors usually appear as a solid mass that brightens with contrast. Additionally, CT can detect calcification of the pineal gland due to increased age.
Treatment of pineal gland tumors and craniopharyngiomas is surgery, if possible. Surgery aims to biopsy and obtain tissue to determine the tumor type and whether it is cancerous. The surgeon will typically remove as much tumor as possible without causing additional symptoms for the individual. Treatments after surgery may include radiation and chemotherapy. Treatment for pineal gland disorders due to injury and chemotherapy.
What are the essential facts to know about the pineal gland?
The pineal gland is a small gland located in the middle of the brain and attached to the roof of the third ventricle. The pineal gland is sometimes referred to as the third eye due to its ability to sense light and dark via the retina. The primary function of the pineal gland is to secrete melatonin, a sleep-promoting hormone. When the environment is dark, the retina sends impulses to the pineal gland to release melatonin and initiate the sleep cycle. Disorders of the pineal gland affect sleep, wakefulness, reproduction, and mood. Examples of pineal gland disorders include pineal tumors, craniopharyngiomas; trauma affecting the sympathetic innervation of the gland; and congenital disorders failing the gland to form. Abnormalities can be detected on MRI and CT imaging. Treatment for pineal gland tumors typically involves surgery and potentially chemotherapy and radiation. Additionally, exogenous administration of the hormones secreted by this endocrine gland, such as melatonin, can be a treatment method.
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Resources for research and reference
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