Pineal Gland Definition
The pineal gland, also known as the “pineal body,” is lightheartedly known as the “third eye” of the human body. This name stems from the pineal gland’s role in secreting melatonin. This hormone, in turn, modulates our sleep and waking patterns. Melatonin was first described by American physician, Dr. Aaron Lerner in 1958. Research has shown melatonin to play an instrumental role in establishing our circadian rhythm, which is the twenty-four-hour cycle of our bioactivity that matches the solar cycle of the day.
Melatonin is one of the most ubiquitous and versatile hormones found in animals and some plants. It is highly lipophilic, which allows it to reach our cells in record time. If its name sounds familiar, it is because melatonin was named after “melanin” after displaying skin lightening effects in frogs. Melatonin derives from the amino acid, tryptophan. This amino acid can be found in humans and other species of mammals, reptiles, birds and amphibians. Tryptophan-rich foods have been linked to calming effects and reduced anxiety. In humans, specifically, melatonin helps control our daily sleep cycle. The body produces melatonin in response to light hitting the retina of the eye. This inhibits the release of melatonin. In contrast, the absence of light at nighttime will be read as a signal to produce more melatonin. The ability to modulate melatonin levels is lent by the presence of special photoreceptor cells in the human retina that emit a signal to the suprachiasmatic nucleus, or SCN, of the hypothalamus. The hypothalamus, in turn, is a part of the brain that supports the body’s homeostatic functions. The light or dark signals are then sent to the pineal gland, which will begin to modulate melatonin levels.
The largest amount of melatonin is expelled by the pineal gland during the night. At this time, the body will undergo several changes closely tied to the concentrations of melatonin. The body’s internal temperature will drop, as will our breathing rate. These experiences are the ones we most associate with falling asleep. In the daytime, however, our retinas will be exposed to a lot of light that will inhibit melatonin expression. This is essential for making us alert and awake during the daytime.
Melatonin has special antioxidant properties. It is known to neutralize radicals, or elements with an unstable electron configuration, that would otherwise cause harmful oxidative damage to tissue. Melatonin can also activate other antioxidant enzymes that will perform restorative functions. Naturally, melatonin is an antiaging substance that declines as we get older. The loss of melatonin is thus associated with various age-related illnesses. Melatonin also retains a role in buffering the immune system in light of seasonal adjustments. Its roles are still being studied, but the consensus lies in melatonin acting as a stimulant under suppressive conditions and as an anti-inflammatory agent when the immune system experiences acute inflammation.
Pineal Gland Location
The pineal gland is roughly located in the center of the brain, sandwiched between the left and right hemispheres. It is about seven by six by three millimeters in dimensions, and is the only midline brain part that is not paired. The pineal body is tucked in the divot or groove where the two thalamic bodies meet. It takes on the shape of a pinecone, which explains its naming! Nearly all existing vertebrates contain a pineal gland. Pineal glands are found in even the primitive lamprey. It makes sense that the pineal gland is a primitive organ, as it is made with the simple intention of acting as a kind of photoreceptor that responds to rays of light. However, not all species have conserved the pineal gland. The exception to the rule is the hagfish, which lacks a perceptible pineal gland. Likewise, a few other more advanced vertebrates have lost theirs sometime in their evolution. Regardless, this light-sensing organ has earned an interesting place in philosophy classes across the world. In its romanticized interpretation, the pineal gland has been described to embody metaphysical properties in the realm of pseudoscience. Like most subjects, this idea was hotly contested by early philosophers. But what remains uncontested is that its secretion, melatonin, serves a vital role in the physical body.
Unlike the remaining mass of the mammalian brain, the pineal gland is not separated from the body by the blood-brain barrier. Instead, it receives the second most profuse supply of blood in the body, next to the kidney. The pineal gland’s main blood supply come from the choroidal branches of the posterior cerebral artery. Its sympathetic (or excitable) innervation, on the other hand, comes from the superior cervical ganglion. The otic ganglia will supply the inhibitory, parasympathetic innervation.
Melatonin receptors are found scattered in various areas of the body. Most notably, they are found in high concentrations in the SCN and the brain’s pituitary gland. This is the main site of action as melatonin directly plays into the circadian rhythm here. But melatonin receptors are also present in the ovaries. The levels of melatonin affect several facets of the menstrual cycle, such as the timing of its onset, the duration, and the frequency. In other animal species, it even acts as a mating cue. For instance, greater levels of melatonin in horses are found during the spring, which coincides with the ideal season for mating. This is a direct example of the solar cycle’s impact on the reproductive cycle via pineal gland activity. Other melatonin receptors lie in the blood vessel walls and in our intestinal tracts. In the gut, melatonin protects the mucosal layers from lesions and irritation via its eradication of free radicals. Gut lesions can lead to painful esophagitis, gastritis, and peptic cancer among other illnesses.
Pineal Gland Disorders
Since the pineal gland is primarily involved in sleep-wake rhythms, it is also takes root in mood disorders. Recent studies have linked chronic stress and poor diet as possible causes of reduced levels of melatonin in the system. This is often found in patients with abnormal circadian cycles of cortisol (or “stress”) hormone. In fact, depression and sexual dysfunction are conditions that are further aggravated by low melatonin output. These of course impact our quality of life. Milder mood alterations, like insomnia and the jetlag that is felt after boarding a long flight, have also been linked to the pineal gland. These feelings are often short-lived, albeit disruptive. Furthermore, peptic ulcers are also linked to melatonin levels when they are too low to prevent oxidative damage.
Pineal cysts, or cysts of the pineal gland, are a relatively common occurrence that happens in about ten percent of people undergoing a CT or MRI scan. The cause of pineal cysts is not known. In fact, most patients with pineal cysts will not display any visible symptoms. But very rarely will patients experience headaches and eye movement abnormalities because of it. In some patients, the cyst can even lead to emotional disturbances, sleep issues, and seizures. Only when the pineal gland cyst is symptomatic will a physician recommend surgical removal. But the overall prognosis for patients with pineal cysts is very good.
Pineal tumors, on the other hand, are a more serious complication that represent about one percent of all brain tumors. At least seventeen types of tumors arise in the area of the pineal gland but many are benign. The most common tumors are gliomas, pineal cell tumors, and germ cell tumors. The pineal gland is located next to a duct called the aqueduct of Sylvius. It acts as a passage through which cerebrospinal fluid (CSF) leaves the center of the brain. Pineal tumors often block this duct, causing a buildup of pressure that expands the ventricles within the skull. This blockage will present complications most often linked to the symptoms of pineal gland tumors:
- Visual changes
- Problems with memory recall
These visual changes include double vision, an inability to properly focus on the objects in front of us, and abnormal eye movements. These issues may improve or resolve once the tumor is either resected or treated. Treatment of the tumor can vary depending on the diagnosis. This diagnosis must be informed with a precise histological analysis from a biopsied sample. A benign, or non-cancerous, pineal tumor can be resected surgically at the hands of a skilled surgeon. However, malignant pineal tumors may be treated with either surgery or radiation therapy. For example, pinealocytomas obtain no benefit from radiation therapy alone. So, they will require surgical resection. The most common cancer in this area is germinoma. Germinoma tumors, in contrast, are both very sensitive to chemotherapy and radiation and will be cured in most cases. The same applies to other malignant germ cell tumors near the pineal gland. Non-germ cell tumors can benefit from newer stereotactic types of radiation therapy. Like any other tissue that has undergone intensive cancer therapy, there may be long term effects on the pineal tissue’s ability to perform its endocrine functions. Therefore, the patient will need to work alongside an endocrinologist to address certain hormone deficiencies that may have arisen. Most of these issues can be managed with medical therapies. This has led the prognosis for pineal tumor survivors – both in children and adults – to improve.
1. How will light affect melatonin secretion? Choose best answer.
C. No effect
2. How will darkness affect melatonin secretion? Choose best answer.
C. No effect
3. Which of the following is indicated for malignant pineal tumors, per the article?
A. Surgical resection
B. Radiation therapy
C. Surgery or radiation
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- Emerson, Charles H (2017). “Pineal Gland.” Encyclopedia Britannica. Retrieved on 2017-07-08 from https://www.britannica.com/science/pineal-gland
- Carillo-Vico, A. et al. (2013). “Melatonin: Buffering the Immune System.” Int J Mol Sci.. 14(4): 8638-8683. Doi: 10.3390/ijms14048638
- NIH (2014). “Pineal Cyst.” Genetic and Rare Diseases Information Center.. Retrieved on 2017-07-07 from https://rarediseases.info.nih.gov/diseases/10723/pineal-cyst
- Ferry, Robert MD (2016). “Pineal Tumor.” E Medicine Health. Retrieved on 2017-07-08 from 2http://www.emedicinehealth.com/script/main/mobileart-emh.asp?articlekey=88561#when_to_seek_medical_care_for_a_pineal_tumor