Pineal gland

The pineal gland, shaped like a pine cone, is one of the major glands of the endocrine system. It is located between the cerebral hemispheres in the center of the brain, where it produces the essential hormone melatonin. Melatonin levels influence the regulation of sleep-wake cycles (feeling sleepy or awake), as well as the development of primary reproductive system organs. Additional functions of the pineal gland are connecting the endocrine and nervous systems (converting signals from the nervous system into hormone signals) and regulating endocrine functions such as growth, metabolism, and homeostasis (maintaining a steady internal environment). Some of the disorders associated with the pineal gland include insomnia, hypotension, seasonal affective disorder, low progesterone ratio, and impaired adrenal function. The pineal gland is sometimes referred to as the "third eye" because of its connectedness with light and its location in the center of the brain.

Background

Located in the middle of the brain, the pineal gland is a small organ—about 1/3 of an inch in length. The gland comprises primarily pineal cells or pinealocytes and nervous system cells or neuroglials and is reddish-grey in color. In X-rays, the pineal gland may appear calcified because of the buildup of calcium, fluoride, and phosphorus deposits over time. The pineal is one of several major glands in the endocrine system, each of which secretes hormones into the blood, which travel to target cells. Responsible for specific cellular activities, these hormones control activities such as the use and storage of water, electrolyte balance, energy, reproduction, growth, and other activities. Out of all the endocrine system glands, the role of the pineal was the last to be discovered. Its primary occupation is the production of melatonin, which plays a key role in maintaining circadian rhythms (sleep-wake cycles) and in regulating sexual development and the secretion of reproductive hormones.

Circadian rhythm refers to the body's twenty-four-hour biological cycle of sleep-wake patterns. What makes melatonin special is that the secretion of this hormone is determined by light exposure to the eyes. That is, exposure to light stops the release of melatonin, while darkness stimulates the brain to produce more melatonin. The low concentrations of melatonin during the day and peak concentrations at night have a major impact upon sleep patterns, as the pineal gland prompts the body to sleep when it is dark and prepares the body to wake up when it is light. This explains why people tend to feel sleepy at night and awake during the day and why their sleeping pattern may change with varying seasonal photoperiods (length of day versus night). More specifically, the retina transmits signals of light and dark exposure to the hypothalamus. These signals are then relayed to the pineal gland, determining how much melatonin is produced and released into the blood.

The second primary role of melatonin and the pineal gland is the regulation of sexual development in human beings and of mating seasons in animals. More specifically, by inhibiting the secretion of reproductive hormones from the pituitary gland, melatonin impacts the development of the male and female reproductive system structures. These pituitary hormones are called gonadotropins (luteinizing hormone and follicle stimulating hormone), and they stimulate the gonads—the primary male and female reproductive organs—to release sex hormones required for their growth and development. In males, the gonads are the testes, and in females, the gonads are the ovaries.

Overview

Since the pineal gland performs many vital body functions, problems in the pineal gland can lead to significant disorders such as insomnia, a sleeping disorder characterized by trouble falling asleep, staying asleep, and lack of sleep. Insomnia, in turn, can lead to chronic fatigue, depression, anxiety, low blood pressure, and stress.

Most pineal gland disorders are caused by an overproduction or deficiency of melatonin secretion. Insomnia is one consequence of low melatonin. Melatonin deficiency can also lead to a stressed immune system, anxiety, low basal temperature, and an increased level of estrogen or progesterone. Health issues connected to an overproduction of melatonin include seasonal affective disorder (SAD), caused by minimal sunlight and shorter days during the winter months, hypotension (low blood pressure), decreased levels of estrogen or progesterone, and poor function of the thyroid and adrenal glands.

In addition, pineal gland function can be affected by any conditions or environmental stresses that disturb the circadian rhythm, such as oscillations in temperature, high altitude, magnetic fields, radiation, and abnormal light and dark rhythms. Disturbances can also occur if someone is exposed to insufficient light during the day or too much light during the night, such as people who do shift work or who experience time zone changes and jet lag. Circadian rhythms can also be imbalanced by poor vision or being blind.

The pineal gland is sometimes subject to cysts and tumors. Pineal gland cysts are most often benign, causing no symptoms or complications and requiring no surgery. Types of pineal gland tumors include pineocytoma, pineoblastoma, and mixed pineal tumors, which can lead to problematic vision, nausea, vomiting, headaches, seizures, and/or impaired memory. In evaluating the risk of performing a biopsy or an open procedure to obtain a tissue diagnosis for a pineal region tumor, studies indicate that X-ray-guided stereotactic biopsy (use of computer imaging to localize a target and guide the removal of the tissue for examination) can be performed safely and effectively at centers familiar with the technique. Studies also show that endoscopic biopsy (the removal of tissue for analysis by instruments inserted in an endoscope, a long thin tube that has a light and video camera), is an effective alternative for experienced surgeons. However, possible drawbacks include limited tissue sampling, limited ability to control bleeding, and the necessity of a second procedure for many patients. Treatment options for malignant pineal tumors include chemotherapy, radiotherapy, and surgery as a first step. Surgery is also considered a "clean-up" procedure for persistent or growing tumors after chemotherapy and radiation.

Bibliography

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