Pineal Gland

Histology

The pineal gland has two types of cells pinealocytes
and glial cells.

• Pinealocytes
  produce melatonin hormone.
• Glial
  cells are supporting brain cells that help neurons and transmit information to
  other cells through neurons.

Vasculature

Unlike the other glands, the pineal gland is not separated from the rest of the body by the blood-brain barrier. After the kidney, this gland receives the most profuse supply of the blood in the body.

The main blood supply comes from the choroidal branches of the posterior cerebral artery. On the other hand, its sympathetic innervation comes from the superior cervical ganglion. While the otic ganglia supply the inhibitory, parasympathetic innervation.

Pituitary gland functions

The pineal gland regulates internal body clock such as sleep-wake cycle, menstrual cycle, and pituitary gland functions. Other functions performed by the pineal gland are sexual development, regulation of melatonin secretion, conversion of nervous system signals into endocrine signals, immune functions and acts as an antioxidant. Let’s discuss all these functions of the pineal gland functions in detail

Melatonin and circadian rhythms

This small endocrine gland within the brain is mainly known to produce the hormone melatonin. Melatonin performs several functions in the body, which are primarily related to conscious brain activities.

Melatonin plays a significant role in inducing sleep and regulating the circadian rhythm of the body. Melatonin is considered as a natural sleep hormone because it produces according to the amount of light exposed to a person. In the dark, it is produced in a higher amount and makes you asleep quickly.

Melatonin
receptors are found mainly in the SCN and brain pituitary gland, and it is the
main site from where melatonin secretes and plays its role in circadian rhythm.
However, the melatonin receptors are also present in ovaries, and its level
affects the onset, duration, and frequency of the menstrual cycle.

Pituitary gland function

Researchers suggest that the pineal gland can alter the behavior of the pituitary and thyroid gland. Besides, melatonin secretion of the pineal gland can stop the pituitary gland from producing essential hormones for the development of ovaries and testes.

Sense of direction

A study shows
that the pineal gland plays an unrecognized role in spatial navigation. People
with impaired pineal gland can decline in a sense of direction.

Mental health

Mental health and sleep are inextricably linked. Inadequate mental health cause sleep deprivation and make it difficult to sleep. Mental health is also connected with access to light. The seasonal affective disorder is a form of depression that affects the person’s mood at a low light level and linked with changes in melatonin secretion.

Melatonin as an Antioxidant

Melatonin has unique antioxidant characteristics and can neutralize the harmful chemicals that damage the tissues. Also, it activates the antioxidant enzymes that perform restorative functions.

Melatonin acts as a natural anti-aging substance, and it declines with age. Hence the loss of melatonin is linked with several age-related illnesses.

Melatonin is
essential for buffering the immune system in light of seasonal adjustments.
More studies are carrying on to prove its anti-inflammatory properties during
immune system inflammation.

Regulation of bone metabolism

Another new
aspect of the pineal gland is to regulate the new bone deposition.
Pineal-derived melatonin mediates its actions through MT2 receptors on bone
cells.  This study could be a potential
target for osteoporosis treatment in the medical field.

Clinical Significance

As an essential
endocrine gland and third eye of the body, the pineal gland has a significant
important clinically. Any abnormality or disorder with this gland function will
cause severe complications that affecting memory, learning, or mood. The
following are some severe disorders that are associated with the Pineal gland.

Pineal Gland Dysfunction

Clinically its significance has been approved, and abnormal pineal gland function may result in many problems. The dysfunction of the pineal gland produces less melatonin secretion, which may result in insomnia, abnormal thyroid function, anxiety, intestinal hyperactivity, and menopause.

Similarly, if
melatonin secretion enhances from a specific limit, then it may cause low blood
pressure, Seasonal Affective Disorder, abnormal adrenal functions.

Disorders that affect sleep and mood

Most prominent pineal gland dysfunction is disturbance in circadian rhythms. Sleeping too much or little or feeling active or restless in the night due to abnormal pineal gland function. Furthermore, one study shows that the pineal gland releases several other chemicals that cause depression, schizophrenia, or mental illness.

Pineal Gland Tumors

Pineal gland tumors are the most severe complication and account for one percent of total brain tumors.  Research shows that almost seventeen types of tumors arise in the pineal gland area, but most of them are benign.

The most common type is a germ cell tumor, which develops from residual embryonic tissue in the gland. Other tumors include gliomas and pineal cell tumors.

The pineal gland is situated near a duct called aqueduct of Sylvius. Pineal tumors block this duct, which is the route of Cerebrospinal fluid and buildup the pressure that expands the ventricles within the skull. This blockage will cause more complications such as

• Seizures
• Nausea
• Headache
• Visual changes
• Problems with memory recall
• Parinaud syndrome (inability to move the eyes
  upwards) Obstruction of the cerebral aqueduct may produce hydrocephalus

Pineal Cysts

Pineal cysts happen in ten percent of people who are undergone MRI scans or CT. However, most people do not have any visible symptoms of pineal cysts. Some patients rarely experience headache and abnormal eye movements.

Also, pineal cysts lead to seizures, sleep issues, and emotional disturbances. Surgical removal from a qualified physician is recommended for the removal of pineal cysts.

Summary/Conclusion

The pineal gland is a tiny pea-size structure found in the middle of the brain and an outward growth of the third ventricle. It has two essential components one is hormone-producing cells called Pinealocytes, and the other is supporting cells that transmit information called glial cells.

The pineal gland produces several hormones, the most important one is melatonin, which helps to regulate biological rhythms such as wake and sleep cycle. Melatonin secretion triggered by darkness and inhibited by light.

The pineal gland is mainly responsible for the nighttime melatonin secretion. Without the proper amount of melatonin hormone, the body would struggle to sleep and wake at the same time.

More researches have been revealing how the pineal gland affects everyday body function and manages other activities. As a principal seat of the soul, it is responsible for many functions in the body, such as regulation of thyroid or pituitary gland functions, sexual development, onset and frequency of menstrual cycle.

Furthermore, one
of the most significant functions of the pineal gland is a sense of direction,
and it helps us to focus on things. Disturbance in pineal gland function leads
to a decline in attention and lack in sense of direction.

Clinically, as opposed to other glands, this gland has a crucial role in the human body, and any defect in the function of the pineal gland may lead to abnormality of other body functions, pineal tumors, or more severe complications.

References

1. "Pineal (as an adjective)". Online Etymology Dictionary, Douglas Harper.
   2018. Retrieved 27 October 2018.
2. Macchi MM, Bruce JN (2004). "Human pineal physiology and
   functional significance of melatonin". Frontiers in Neuroendocrinology. 25 (3–4):
   177–95. doi:10.1016/j.yfrne.2004.08.001. PMID 15589268.
3. Arendt J, Skene DJ (February 2005). "Melatonin as a
   chronobiotic". Sleep Medicine Reviews. 9 (1):
   25–39. doi:10.1016/j.smrv.2004.05.002. PMID 15649736.
4. Bowen R. "The Pineal Gland and Melatonin". Archived from the original on 24 November 2011.
   Retrieved 14 October 2011.
5. Chen CY, Chen FH, Lee CC, Lee KW, Hsiao HS (October 1998). "Sonographic characteristics of the cavum
   velum interpositum" (PDF). AJNR. American Journal of
   Neuroradiology. 19 (9): 1631–5. PMID 9802483.
6. Dorland's. Illustrated Medical Dictionary. Elsevier
   Saunders. p. 1607. ISBN 978-1-4160-6257-8.
7. Pritchard TC, Alloway KD (1999). Medical Neuroscience (Google books preview). Hayes Barton Press. pp. 76–77. ISBN 978-1-889325-29-3. Retrieved 8 February 2009.
8. Arendt J: Melatonin and the Mammalian Pineal Gland, ed 1.
   London. Chapman & Hall, 1995, p 17