The pineal gland is a small, pinecone-shaped gland of the endocrine system. A structure of the diencephalon of the brain, the pineal gland produces the hormone melatonin. Melatonin influences sexual development and sleep-wake cycles. The pineal gland is composed of cells called pinealocytes and cells of the nervous system called glial cells. The pineal gland connects the endocrine system with the nervous system in that it converts nerve signals from the sympathetic system of the peripheral nervous system into hormone signals. Over time, calcium deposits build-up in the pineal and its accumulation can lead to calcification in the elderly.
The pineal gland is involved in several functions of the body including:
- Secretion of the hormone melatonin
- Regulation of endocrine functions
- Conversion of nervous system signals to endocrine signals
- Causes sleepiness
- Influences sexual development
- Influences immune system function
- Antioxidant activity
Directionally the pineal gland is situated between the cerebral hemispheres and attached to the third ventricle. It is located in the center of the brain.
Pineal Gland and Melatonin
Melatonin is produced within the pineal gland and synthesized from the neurotransmitter serotonin. It is secreted into the cerbrospinal fluid of the third ventricle and is directed from there into the blood. Upon entering the bloodstream, melatonin can be circulated throughout the body. Melatonin is also produced by other body cells and organs including retinal cells, white blood cells, gonads, and skin.
Melatonin production is vital to the regulation of sleep-wake cycles (circadian rhythm) and its production is determined by light and dark detection. The retina sends signals about light and dark detection to an area of the brain called the hypothalamus. These signals are eventually relayed to the pineal gland. The more light detected, the less melatonin produced and released into the blood. Melatonin levels are at their highest during the night and this promotes changes in the body that help us to sleep. Low levels of melatonin during daylight hours help us to stay awake. Melatonin has been used in the treatment of sleep-related disorders including jet lag and shift-work sleep disorder. In both of these cases, a person's circadian rhythm is disrupted either due to travel across multiple time zones or due to working night shifts or rotating shifts. Melatonin has also been used in the treatment of insomnia and depressive disorder.
Melatonin influences the development of reproductive system structures as well. It inhibits the release of certain reproductive hormones from the pituitary gland that affect male and female reproductive organs. These pituitary hormones, known as gonadotropins, stimulate gonads to release sex hormones. Melatonin, therefore, regulates sexual development. In animals, melatonin plays a role in regulating mating seasons.
Pineal Gland Dysfunction
Should the pineal gland begin to function abnormally, a number of problems may result. If the pineal gland is not able to produce sufficient amounts of melatonin, a person could experience insomnia, anxiety, low thyroid hormone production (hypothyroidism), menopause symptoms, or intestinal hyperactivity. If the pineal gland produces too much melatonin, a person could experience low blood pressure, abnormal function of the adrenal and thyroid glands, or Seasonal Affective Disorder (SAD). SAD is a depressive disorder that some individuals experience during the winter months when sunlight is minimal.
- Emerson, Charles H. “Pineal Gland.” Encyclopædia Britannica, Encyclopædia Britannica, www.britannica.com/science/pineal-gland.
- Britannica, The Editors of Encyclopaedia. “Melatonin.” Encyclopædia Britannica, Encyclopædia Britannica, www.britannica.com/science/melatonin.